Drilling Fluids
Dione oil co. has developed special methods for cost estimation of required fluids and chemicals when drilling & gas wells. The mentioned models has been implemented into the assemblies. In order to become familiar with the assemblies faetures we need to describe the general functions of a drilling fluids which is shown in the following text.
The basic ingredients of muds are water (water based muds), oil( oil based muds), or salt –water (salt –water based muds ). Desirable properties for specific condition are obtained by adding various materials such as clay and chemical additives to this mixture.
The ability of a mud to suspend cutting during period of a non- circulation primarily depends on its gel strength .
If a mud doesn’t have gel strength during periods of non-circulation, cutting will settles above the bit or at the top of the drill collars. This action causes the pipe to become stuck and will result an expensive fishing job. it should be mentioned that in hard rock areas where penetration rate is low , so a relatively small quantity of cutting is in the following categories:
1-1- Liquids
The liquids that are used in drilling fluids are:
fresh water, salt water and oil. fresh water is suitable for drilling , because of its low viscosity and density. salt water is better than Fresh water.
10%salt in water improves its density and produces upper hydrostatic pressure . oil can produce lower hydrostatic pressure .because its density is lower .
Drilling with fresh water is caused the expansion of clay which present in sandstones. this expansion is due to te absorption .of water . this problem , fills the porous of sandstone s and in oil well drilling , oil can not enter (penetrate) to the well. Due to this problem, salt water is better than fresh water.
1-2- oil mude+8
Drilling fluids are called muds. if the continuous phase (liquid base) is composed of a liquid hydrocarbon, especially low flammable hydrocarbons, these muds will be suitable for sandstone drilling Also, oil can reduce the density of muds . No . 2 diesel usually is used for the oil phase because of its viscosity characteristics , low flammability ,and low solvency for rubber (some pars of BOP are made from rubbers). The water which presents in an oil mud is in the form of an emulsion , the advantage and disadvantages of using oil muds are summarized in table 1 . Because of the higher initial cost and pollution control problem associated with oil muds , they are used much less frequently than water – based muds .
The most common application of oil muds include:
- To cool and lubricate the bit and drill string .
- To remove and transport cutting form the bottom of the hole to the surface.
- To suspend cutting in the annuals during times when circulation is stopped.
- To control encountered subsurface pressures and prevention of lost circulation.
The basic ingredients of muds are water (water based muds), oil( oil based muds), or salt –water (salt –water based muds ). Desirable properties for specific condition are obtained by adding various materials such as clay and chemical additives to this mixture.
The ability of a mud to suspend cutting during period of a non- circulation primarily depends on its gel strength .
If a mud doesn’t have gel strength during periods of non-circulation, cutting will settles above the bit or at the top of the drill collars. This action causes the pipe to become stuck and will result an expensive fishing job. it should be mentioned that in hard rock areas where penetration rate is low , so a relatively small quantity of cutting is in the following categories:
1-1- Liquids
The liquids that are used in drilling fluids are:
fresh water, salt water and oil. fresh water is suitable for drilling , because of its low viscosity and density. salt water is better than Fresh water.
10%salt in water improves its density and produces upper hydrostatic pressure . oil can produce lower hydrostatic pressure .because its density is lower .
Drilling with fresh water is caused the expansion of clay which present in sandstones. this expansion is due to te absorption .of water . this problem , fills the porous of sandstone s and in oil well drilling , oil can not enter (penetrate) to the well. Due to this problem, salt water is better than fresh water.
1-2- oil mude+8
Drilling fluids are called muds. if the continuous phase (liquid base) is composed of a liquid hydrocarbon, especially low flammable hydrocarbons, these muds will be suitable for sandstone drilling Also, oil can reduce the density of muds . No . 2 diesel usually is used for the oil phase because of its viscosity characteristics , low flammability ,and low solvency for rubber (some pars of BOP are made from rubbers). The water which presents in an oil mud is in the form of an emulsion , the advantage and disadvantages of using oil muds are summarized in table 1 . Because of the higher initial cost and pollution control problem associated with oil muds , they are used much less frequently than water – based muds .
The most common application of oil muds include:
- Drilling deep hot formations , potash or active shale formations(temperatures> 300 f)
- Drilling salt , anhydrate , corallites, potash or active shale formations or formations containing H2S or CO2
- Drilling Producing formations easily damaged by water – based muds
- Corrosion control
- Drilling directional or slim holes where high torque is a problem
- Preventing or freeing stuck pipe
| DISADVANTAGES | ADVANTAGES |
| Higher initial cost | Good rheological properties at temperature as high as 500 |
| Requires more stringent pollution control procedures | more inhibitive than inhibitive water base muds |
| Remedial treatment for lost circulation in more difficult | effective against all types of corrosion |
| Detection of gas kicks is more difficult because of gas solubility in diesel oil | superior lubricating characteristics |
| Reduce effectiveness of some logging tools | permits mud densities |
1-3- Emulsions Muds
The most common emulsion muds are oil in water types , in which the oil is the dispersed phase and exists as small individual droplets.
the amount of oil is in the range of 10 to 15 % of muds and can increase to 50 % . the base mud may e any type fresh or salt water . Clay , solids and weighting materials may be added if desired . Oil in water emulsion muds are better for lubrication of bit and drill string in rotary drilling system .
In many areas considerable thicknesses of rock salt must be penetrated. Solution of these beds in mud can cause excessive holes en largamente which may be a source of future troubles and expenses. The principal means of avoiding these problems is to prepare a salt saturated mud system prior to prepare drilling the salt.
A blowout occurs when encountered formation pressures exceed the mud column pressure, which allows the formation fluids to blow out of the hole , proper mud density is the principle factor in avoiding this problem . Blowout is recognized by increasing level of mud in pit, excessive pressure of return mud , or too rapid withdrawal of the drill string to the surface.
lost circulation is defined as the loss of substantial quantities of whole mud to an encountered formation . lost circulation depends on density of mud and occurs when formation permeability is too large to be plugged by the clay and solids . Other lost circulations materials that commonly circulate in the mud system are shredded wood, cotton, lamellate mica, nutshell, prelates ,etc.
1-4-Gases
Some gases are used for drilling such as : Air, Methane, Nitrogen and Carbon Dioxide . Methane has tendency to compose with air . So it is not appropriate. Only air can be used in operation . Air is light , cheap and best cleaner .
The drilling engineer is responsible for the selection and maintenance of the best drilling fluid for the job . The drilling fluid relates either directly or indirectly to most drilling problems.
if the drilling fluids does not perform adequately the necessary functions, it could become necessary to abandon the well . also, the required additives to maintain the drilling fluid in good condition can be quite expensive . Drilling fluids cost often exceeds $ 1 million on a single deep well in some areas. A drilling fluid specialist called a mud engineer frequently is kept on duty at all times to maintain the drilling fluids in good condition at the lower possible cost.
2- Circulation system
A major function of the fluid circulating system is to remove the rock cuttings form the hole as drilling Progresses. The drilling mud travels
Triplex pumps are lighter and more than duplex pumps , their output pressure pulsations are not as great as duplex pumps, and they are cheaper to operate. for theses reasons , the majority of new pump being place into operation are of the triplex design.
the advantages of the reciprocating positive displacement pumps are:
Mechanical efficiency usually is assumed to be 90% and relates to the efficiency of the prime mover itself and the linkage to the pump drive shaft. Volumetric efficiency of a pump is adequately changed can be as high as 100%.
Generally , two circulating pumps are installed on the rig . for the large hole sizes. used on the shallow portion of most wells, both pump can be operated in parallel to deliver the large flow rates required . on the deeper portions of the well. only one pump is needed , and the second pump maintenance is required .
The flow conduits which connect the mud pumps to the drill string include:
The discharge line also contains a pressure relief valve to prevent line rupture in the event that the pump is started against a closed valve .
The stand pipe and rotary hose provide a flexible connection to permits vertical movement of the drill string . the swivel contains roller bearings to support the rotating pressure seal that allows fluid circulation through the swivel . The Kelly , is a rectangular or hexagonal cross section pipe that allows the drill string to be rotated.
In new drilling system Kelly and swivel are removed and replaced with top drive .
mud pits are required for holding an excess volume of drilling mud at the surface . this surface volume allows time for setting the finer rock cutting and for the release of entrained gas bubbles not mechanically separated . Also , in the event some drilling fluid is lost to underground formation , this fluid loss is replaced by mud form the surface pits. Some times , the settling and suction pits are dug in the earth with a bulldozer but more commonly are made of steel. A large earthen reserve pit is provide for contaminated or discarded drilling fluid and for the rock cuttings.
Dry mud additives often are stored is sacks, which are added manually to the suction pit using a mud mining hopper . liquid mud additives can be added to the suction pit form a chemical tank .
mud jets or motor – driven agitators often are mounted on pits for auxiliary mining.
The contaminant – removing equipment includes mechanical devices for removing solids and gases from the mud.
The coarse rock cutting and caving are removed by the shale shaker. Additional separation of solids and gases from the mud occurs in solid control equipments. when the amount of finely ground solids in the mud becomes too great , they can be removed by hydro cyclones and decanting centrifuges. A hydro cyclones is a cone shaped housing that imparts a whirling fluid motion much like a tornado . The heavier solids in mud are thrown to The housing of the hydro clones and fall through the apex at the bottom. Most of liquid and lighter particles exit through the vortex finder at the top. the decanting center fudge consists of a routing cone – shaped drum which has a screw conveyor attached to its interior .
Rotation of the cone creates a centrifugal force that throws the heavier particle to the outer housing . the screw conveyor moves the separated particles to the discharge.
When the amount of entrained formation gas that leaves the settling pit becomes too great , it can be separated by using a degasser . A vacuum pump mounted on top of the chamber removes the gas from the chamber .
the mud flows across inclined flat surface in the chamber in thin layers , which allows the gas bubbles have enlarged by the reduced pressure to be separated from the mud more easily . mud is drown through the chamber at a reduced pressure of a bout 5 psia by a mud jet located in the discharge line.
3- solids Control
Solids controls are classified in two groups:
Solids control for un weighted muds and solids control for weighted muds.
3-1-solides control for un weighted muds
The solids in a mud often are classified as cither inert or active . The inert solids are those that do not or otherwise react with other components of the mud . the inert solids include such minerals as sand , silt , limestone , feldspar, and API barite. With the exception of API barite, which is used to increase the mud density , these inert solids usually are considered undesirable in mud.
They increase the frfrictional pressure drop in fluid system but do not greatly increase the ability to carry the rock cutting to the surface. The formed filter cake from these solids is thick and permeable rather than thin and relatively impermeable.
The filter cake is a layer of solids that remains on the standard filter paper under standard test condition.
solids have a direct effect on many drilling problems including stuck pipe , excessive pipe torque and drag , loss of circulation, and poor cement bonding to the formation.
Table 2 cut point ranges
The most common emulsion muds are oil in water types , in which the oil is the dispersed phase and exists as small individual droplets.
the amount of oil is in the range of 10 to 15 % of muds and can increase to 50 % . the base mud may e any type fresh or salt water . Clay , solids and weighting materials may be added if desired . Oil in water emulsion muds are better for lubrication of bit and drill string in rotary drilling system .
In many areas considerable thicknesses of rock salt must be penetrated. Solution of these beds in mud can cause excessive holes en largamente which may be a source of future troubles and expenses. The principal means of avoiding these problems is to prepare a salt saturated mud system prior to prepare drilling the salt.
A blowout occurs when encountered formation pressures exceed the mud column pressure, which allows the formation fluids to blow out of the hole , proper mud density is the principle factor in avoiding this problem . Blowout is recognized by increasing level of mud in pit, excessive pressure of return mud , or too rapid withdrawal of the drill string to the surface.
lost circulation is defined as the loss of substantial quantities of whole mud to an encountered formation . lost circulation depends on density of mud and occurs when formation permeability is too large to be plugged by the clay and solids . Other lost circulations materials that commonly circulate in the mud system are shredded wood, cotton, lamellate mica, nutshell, prelates ,etc.
1-4-Gases
Some gases are used for drilling such as : Air, Methane, Nitrogen and Carbon Dioxide . Methane has tendency to compose with air . So it is not appropriate. Only air can be used in operation . Air is light , cheap and best cleaner .
The drilling engineer is responsible for the selection and maintenance of the best drilling fluid for the job . The drilling fluid relates either directly or indirectly to most drilling problems.
if the drilling fluids does not perform adequately the necessary functions, it could become necessary to abandon the well . also, the required additives to maintain the drilling fluid in good condition can be quite expensive . Drilling fluids cost often exceeds $ 1 million on a single deep well in some areas. A drilling fluid specialist called a mud engineer frequently is kept on duty at all times to maintain the drilling fluids in good condition at the lower possible cost.
2- Circulation system
A major function of the fluid circulating system is to remove the rock cuttings form the hole as drilling Progresses. The drilling mud travels
- form the steel tanks to the mud pump,
- form the mud pump through the high pressure surface connections to the drill string,
- through the drill string to the bit,
- through the nozzles of the bit and up the annual space between the drill string and hole to the surface , and
- through the contaminant removal equipment back to the suction tank.
- mud pumps,
- mud pits,
- mud mixing equipment, and
- contaminant removal equipment.
Triplex pumps are lighter and more than duplex pumps , their output pressure pulsations are not as great as duplex pumps, and they are cheaper to operate. for theses reasons , the majority of new pump being place into operation are of the triplex design.
the advantages of the reciprocating positive displacement pumps are:
- the ability to move high solids content fluids laden with abrasives,
- ability to pump large particles,
- ease of operation and maintenance,
- reliability , and
- ability to operate over a wide range of pressure and flow rates by changing the diameters of the pump liners ( compression cylinders) and pistons.
Mechanical efficiency usually is assumed to be 90% and relates to the efficiency of the prime mover itself and the linkage to the pump drive shaft. Volumetric efficiency of a pump is adequately changed can be as high as 100%.
Generally , two circulating pumps are installed on the rig . for the large hole sizes. used on the shallow portion of most wells, both pump can be operated in parallel to deliver the large flow rates required . on the deeper portions of the well. only one pump is needed , and the second pump maintenance is required .
The flow conduits which connect the mud pumps to the drill string include:
- a surge chamber ,
- heavy –walled pipe which connect the pump to a pump manifold located on the rig floor,
- a standpipe and rotary hose,
- a swivel , and
- a Kelly.
The discharge line also contains a pressure relief valve to prevent line rupture in the event that the pump is started against a closed valve .
The stand pipe and rotary hose provide a flexible connection to permits vertical movement of the drill string . the swivel contains roller bearings to support the rotating pressure seal that allows fluid circulation through the swivel . The Kelly , is a rectangular or hexagonal cross section pipe that allows the drill string to be rotated.
In new drilling system Kelly and swivel are removed and replaced with top drive .
mud pits are required for holding an excess volume of drilling mud at the surface . this surface volume allows time for setting the finer rock cutting and for the release of entrained gas bubbles not mechanically separated . Also , in the event some drilling fluid is lost to underground formation , this fluid loss is replaced by mud form the surface pits. Some times , the settling and suction pits are dug in the earth with a bulldozer but more commonly are made of steel. A large earthen reserve pit is provide for contaminated or discarded drilling fluid and for the rock cuttings.
Dry mud additives often are stored is sacks, which are added manually to the suction pit using a mud mining hopper . liquid mud additives can be added to the suction pit form a chemical tank .
mud jets or motor – driven agitators often are mounted on pits for auxiliary mining.
The contaminant – removing equipment includes mechanical devices for removing solids and gases from the mud.
The coarse rock cutting and caving are removed by the shale shaker. Additional separation of solids and gases from the mud occurs in solid control equipments. when the amount of finely ground solids in the mud becomes too great , they can be removed by hydro cyclones and decanting centrifuges. A hydro cyclones is a cone shaped housing that imparts a whirling fluid motion much like a tornado . The heavier solids in mud are thrown to The housing of the hydro clones and fall through the apex at the bottom. Most of liquid and lighter particles exit through the vortex finder at the top. the decanting center fudge consists of a routing cone – shaped drum which has a screw conveyor attached to its interior .
Rotation of the cone creates a centrifugal force that throws the heavier particle to the outer housing . the screw conveyor moves the separated particles to the discharge.
When the amount of entrained formation gas that leaves the settling pit becomes too great , it can be separated by using a degasser . A vacuum pump mounted on top of the chamber removes the gas from the chamber .
the mud flows across inclined flat surface in the chamber in thin layers , which allows the gas bubbles have enlarged by the reduced pressure to be separated from the mud more easily . mud is drown through the chamber at a reduced pressure of a bout 5 psia by a mud jet located in the discharge line.
3- solids Control
Solids controls are classified in two groups:
Solids control for un weighted muds and solids control for weighted muds.
3-1-solides control for un weighted muds
The solids in a mud often are classified as cither inert or active . The inert solids are those that do not or otherwise react with other components of the mud . the inert solids include such minerals as sand , silt , limestone , feldspar, and API barite. With the exception of API barite, which is used to increase the mud density , these inert solids usually are considered undesirable in mud.
They increase the frfrictional pressure drop in fluid system but do not greatly increase the ability to carry the rock cutting to the surface. The formed filter cake from these solids is thick and permeable rather than thin and relatively impermeable.
The filter cake is a layer of solids that remains on the standard filter paper under standard test condition.
solids have a direct effect on many drilling problems including stuck pipe , excessive pipe torque and drag , loss of circulation, and poor cement bonding to the formation.
Table 2 cut point ranges
| cut point range (micron) | Hydro cyclone diameter (in) |
| 40 | 6 |
| 20 | 4 |
| 10 | 2 |
Four basic methods are used to prevent the concentration of solids in the mud from increasing to an undesirable level . these are:
Screening always is applied first in processing the annular mud stream . recent developments in screening equipment have made possible the use of extremely fine screens.
this allows the removal of most the solids before their size has been reduced to the size of the API barite particles . API specifications for Commercial barium sulfate require that 97% of the particles pass through a 200- mesh screen . A 200- mesh screen has 200 opening per inch . Particles less than about 74 microns in diameter will pass through a typical 200-mesh screen .
Screen sizes below 200-mesh cannot be used with weighted muds , because of the cost of replacing the API barite discarded with the solids.
The natural settling rate of drilled solids is much too low for settling pits to be effective. Thus, devices such as hydro cyclones and centrifuges are used to increase the gravitational force acting on the particles. At present , both the hydro cyclones and high- speed centrifuges are being used as forced settling devices with un weighted muds.
The cut point of a hydro cyclone is the particle size at which half the particles of that size are discarded . the rated points of several common hydro cyclones are shown in table 2.
Sine the particle – size range of API barite is usually about 2 to 80 microns, Hydro cyclone cannot be used with weighted muds unless they are used in series with a screen . Centrifuges operate at high revolutions per minutes and have a contoured bowl . A Conical bowl has been developed for use on un weighted mud systems downstream of the small hydro cyclones .
The contoured bowl increase the path length of the solids in the centrifuge and allows finer solids to be separated. The centrifuge overflow primarily contains solids less than 6 microns in diameter .
The removal of fine active clay particles can be facilitated by adding chemicals that cause the clay particles to flocculate or agglomerate into larger unites . When the agglomerate of the clay particles has been achieved , separation can be accomplished more easily by settling .
The concentration of the solids not removed by screening or forced settling can be reduced by dilution . Because of the limited storage capacity of the active mud pits , dilution requires discarding some of the mud to the reserve pit. Dilution . thus, requires discarding a portion of the additives used in previous mud treatments
in addition ,the new mud created by adding of water must be brought to the desired density and chemical content . To keep the cost of dilution low , the mud volume should be kept limit. Old mud should be discarded before dilution rather than after dilution . also, the cost of a large one- step dilution is less than frequent small dilutions . the cost of dilution increases rapidly with mud density .
Dilution water is introduced upstream of the hydro cyclones to increase their separation efficiency . Chemical treatment normally is made downstream of all separation equipment .
2-3- solids control for weighted muds
The addition of solids for increasing density lowers the amount of inert formation solids that can be tolerated . The ideal composition of weighted mud is:
Hydro cyclones cannot be used alone on weighted system , because their cut points fall in the particle – size range of the API barite.
A series arrangement of a hydro cyclone and a shaker screen is called a mud cleaner . it is suitable for muds of moderate density (below 151bm/gal).
The fine solids that pass through the screen can be handled by dilution and deflocculating.
At higher densities , the mud cleaners are much less efficient . Most of the coarse solids in the mud remain in liquid stream exiting on top of the unit and , thus , by pass , the screen . Also , dilution requires discarding a large volume of API barite with a portion of the old mud and the cost of dilution can become quite high. In this situation , centrifuges often are employed to separate the particle having sizes that fall in the API barite range from the liquid and extremely find solids . in this manner , the mud stream is divided into 1 ) allow density over flows slurry (approximately 9 . 51 bm / gal ) and 2 ) a high density slurry (approximately 231 bm/ gal ).
The high density slurry is returned to the active mud system , and the low density slurry usually is discarded.
About three – fourth of the betonies and chemical content of the mud is discarded with the fine solids when the centrifuge is used.
New betonies and chemicals must be added to prevent depleting the mud . also , since some of the API barite and drilled solids are discarded in the over flow , the volume of mud which reclaimed from the underflow will less than the volume of mud processed .
A small additional volume of new mud must be built in order to maintain the total mud volume constant. A material balance calculation can be made to determine the proper amounts of required API barite , clay, chemicals , and water to recon structure a barrel of mud that has been processed with a centrifuge.
3-3- Control of solids and water content in oil muds
Hydro cyclones and centrifuges cannot be used economically on oil muds since significant volume of the expensive liquid phase would be discarded by these devises. Dilution is also quite expensive.
Screening is the only economical means of solids control of oil muds . Since oil muds are inhibitive , cutting disintegration is limited and screens are very effective .Using several screens in series , usually is possible to screen the returning mud stream as fine as 200- mesh .
When the desired solids level cannot be maintained by screening , dilution will be required.
The water content of oil muds also must be maintained within limits . When the mud temperature is high , water evaporation will be significant . Evaporation losses must be replaced to prevent changing the salinity and activity of the mud . in addition , if the saline solution becomes saturated , the precipitation of salts can causes a decrease in the emulsion stability . the water content shall be decreased when increasing mud density in order to prevent excessive viscosity . This is accomplished by dilution with oil .
4- Solids control Equipment
A solids control equipment given in table 3. In this table the size range of solids that is removed by equipment type and primary application of these equipment are specified. Some advantage of good solids control equipment are:
Primer screen belts are available in 5,10,20 and 30 mesh sizes .
A counter routing cleaning brush is available under belts for cleaning.
Flow line primer is effective for removal of hydrated clays from inhibited and uninhibited mud system and removal of large drilled cutting .
Inhibitive muds prevent formation solids from disintegrating into extermely small particles.
Deck angle of shaker is Adjustable while Drilling (AWD) (-1 to 10 degrees) for optimizing shaker performance .
Shakers are designed in 3 and 4 panels . for Example , fluid retention capability at 5 degrees uphill is 144 liters for 3- panel shakers and 257 liters for 4- panel shakers.
Table 3 Solids control equipment
- Screening
- Forced Settling
- Chemical Flocculation
- Dilution
Screening always is applied first in processing the annular mud stream . recent developments in screening equipment have made possible the use of extremely fine screens.
this allows the removal of most the solids before their size has been reduced to the size of the API barite particles . API specifications for Commercial barium sulfate require that 97% of the particles pass through a 200- mesh screen . A 200- mesh screen has 200 opening per inch . Particles less than about 74 microns in diameter will pass through a typical 200-mesh screen .
Screen sizes below 200-mesh cannot be used with weighted muds , because of the cost of replacing the API barite discarded with the solids.
The natural settling rate of drilled solids is much too low for settling pits to be effective. Thus, devices such as hydro cyclones and centrifuges are used to increase the gravitational force acting on the particles. At present , both the hydro cyclones and high- speed centrifuges are being used as forced settling devices with un weighted muds.
The cut point of a hydro cyclone is the particle size at which half the particles of that size are discarded . the rated points of several common hydro cyclones are shown in table 2.
Sine the particle – size range of API barite is usually about 2 to 80 microns, Hydro cyclone cannot be used with weighted muds unless they are used in series with a screen . Centrifuges operate at high revolutions per minutes and have a contoured bowl . A Conical bowl has been developed for use on un weighted mud systems downstream of the small hydro cyclones .
The contoured bowl increase the path length of the solids in the centrifuge and allows finer solids to be separated. The centrifuge overflow primarily contains solids less than 6 microns in diameter .
The removal of fine active clay particles can be facilitated by adding chemicals that cause the clay particles to flocculate or agglomerate into larger unites . When the agglomerate of the clay particles has been achieved , separation can be accomplished more easily by settling .
The concentration of the solids not removed by screening or forced settling can be reduced by dilution . Because of the limited storage capacity of the active mud pits , dilution requires discarding some of the mud to the reserve pit. Dilution . thus, requires discarding a portion of the additives used in previous mud treatments
in addition ,the new mud created by adding of water must be brought to the desired density and chemical content . To keep the cost of dilution low , the mud volume should be kept limit. Old mud should be discarded before dilution rather than after dilution . also, the cost of a large one- step dilution is less than frequent small dilutions . the cost of dilution increases rapidly with mud density .
Dilution water is introduced upstream of the hydro cyclones to increase their separation efficiency . Chemical treatment normally is made downstream of all separation equipment .
2-3- solids control for weighted muds
The addition of solids for increasing density lowers the amount of inert formation solids that can be tolerated . The ideal composition of weighted mud is:
- Water
- Active clay
- Inert weigh material
Hydro cyclones cannot be used alone on weighted system , because their cut points fall in the particle – size range of the API barite.
A series arrangement of a hydro cyclone and a shaker screen is called a mud cleaner . it is suitable for muds of moderate density (below 151bm/gal).
The fine solids that pass through the screen can be handled by dilution and deflocculating.
At higher densities , the mud cleaners are much less efficient . Most of the coarse solids in the mud remain in liquid stream exiting on top of the unit and , thus , by pass , the screen . Also , dilution requires discarding a large volume of API barite with a portion of the old mud and the cost of dilution can become quite high. In this situation , centrifuges often are employed to separate the particle having sizes that fall in the API barite range from the liquid and extremely find solids . in this manner , the mud stream is divided into 1 ) allow density over flows slurry (approximately 9 . 51 bm / gal ) and 2 ) a high density slurry (approximately 231 bm/ gal ).
The high density slurry is returned to the active mud system , and the low density slurry usually is discarded.
About three – fourth of the betonies and chemical content of the mud is discarded with the fine solids when the centrifuge is used.
New betonies and chemicals must be added to prevent depleting the mud . also , since some of the API barite and drilled solids are discarded in the over flow , the volume of mud which reclaimed from the underflow will less than the volume of mud processed .
A small additional volume of new mud must be built in order to maintain the total mud volume constant. A material balance calculation can be made to determine the proper amounts of required API barite , clay, chemicals , and water to recon structure a barrel of mud that has been processed with a centrifuge.
3-3- Control of solids and water content in oil muds
Hydro cyclones and centrifuges cannot be used economically on oil muds since significant volume of the expensive liquid phase would be discarded by these devises. Dilution is also quite expensive.
Screening is the only economical means of solids control of oil muds . Since oil muds are inhibitive , cutting disintegration is limited and screens are very effective .Using several screens in series , usually is possible to screen the returning mud stream as fine as 200- mesh .
When the desired solids level cannot be maintained by screening , dilution will be required.
The water content of oil muds also must be maintained within limits . When the mud temperature is high , water evaporation will be significant . Evaporation losses must be replaced to prevent changing the salinity and activity of the mud . in addition , if the saline solution becomes saturated , the precipitation of salts can causes a decrease in the emulsion stability . the water content shall be decreased when increasing mud density in order to prevent excessive viscosity . This is accomplished by dilution with oil .
4- Solids control Equipment
A solids control equipment given in table 3. In this table the size range of solids that is removed by equipment type and primary application of these equipment are specified. Some advantage of good solids control equipment are:
- Optimizing removal of native solids .
- Minimizing fluid loss.
- Reducing required dilution volume
- Reducing disposal coasts
- Increasing rate of penetration
- Decreasing time to total depth
- Reducing noise level
Primer screen belts are available in 5,10,20 and 30 mesh sizes .
A counter routing cleaning brush is available under belts for cleaning.
Flow line primer is effective for removal of hydrated clays from inhibited and uninhibited mud system and removal of large drilled cutting .
Inhibitive muds prevent formation solids from disintegrating into extermely small particles.
Deck angle of shaker is Adjustable while Drilling (AWD) (-1 to 10 degrees) for optimizing shaker performance .
Shakers are designed in 3 and 4 panels . for Example , fluid retention capability at 5 degrees uphill is 144 liters for 3- panel shakers and 257 liters for 4- panel shakers.
Table 3 Solids control equipment
| Name | Range | Mud Type |
| flo-line primer | 100 microns & larger | all |
| shale shaker | 76 microns & larger | all |
| decanter | 40 microns & larger | unweighted |
| disinter | 20 microns & larger | unweighted |
| centrifuge | 0-12 microns &larger | weighted & unwelghted |
4-2- flo divider
Flo divider ensures even liquid and drilled solids distribution to downstream shakers.
Using a flo divider maximizes solids removal capabilities of the shale shakers by ensuring each individual shaker receives an equal distribution of both drilling fluids and drilled solids and eliminates the requirement for a back tank.
4-3- shaker
The continuous liner motion shale shaker system engineered for optimal solids removal .
A high g shaker benefits are:
Maximum flow rate of a screen is directly related to the open area that mud can FLOW THROUGH and the open area that mud can flow through and wire thickness. Two screens with the same openings and with different wire dimension will have different flow CAPACITIES.
The screen with the smaller wire diameter will have a greater flow capacity and also a shorter LIFE.
selection of best screen depends on money , conditions of hole , mud dilution , drilling time and amount of solids in mud .
We use cut point for SCREENS. The phase “d50 cut point is 69 microns “ means that 50% of the 69 microns particles will be rejected and 50 % will pass through the screen or “16d cut point is 49 microns “ means that 16% of the 49 microns particles will be rejected and 84% will pass through the screen .
Derrick screens are manufactured in DX ,PWP < PM and PMD names .
Derrick DX series developed in 1974 and PWP technology developed in 1984.
the screen –life of PWP is longer than DX because PWP has metal backing plate and DX has plastic backing plate.
PMD developed in 1994 by Derrick to increase capacity of screen and PMD+ developed in 1996 . PMD increase the usable screen area to 125% .
The old versions are only able to attend adequate screen life with plastic – backed screen by increasing wire diameters.
Due to the reduced open area from the increase wire diameters, the screen nominal opening must be increased to maintain sufficient capacity . these relatively coarser screens cause solids to increase in the mud system . So, dilution requirement s and mud cost will increase.
Dilution costs can vary dramatically depending which brands of screen are used . for example , for a 9800 HOLE. section of 12-1/4 INCH, hole with a target drilled solids content of 7%, the following dilution expenses could be incurred :
4-4- Hydro cyclone
Hydro cyclone are essential for removing solids on un weighted systems.
Hydro cyclone appear very simple, easy to change part s , and easy to adjust. we need to understand the principles because this allows us to operate the cones efficiently and economically .
Feed slurry fed through the inlet at high velocity obtained by steady pressure of feet head . A centrifugal pump is used to obtain the desired head so, it is important that the pump is sized correctly . The high velocity entering the feed chamber creates a spinning velocity and resulting centrifugal forces and the vortex finder causes the stream to spiral down wards.
Centrifugal force and inertia cause the solids to settle outwards the hydro cyclone wall in a downward stream . As the cone section narrows, the downward spinning liquid moves towards the center and back up the cone . Hydro cyclone cut point is affected by :
A balance design hydro cyclone operate ineffective with rope type underflow discharge.
Rope discharge is the inefficient way to run cones and increase concentration of solid in underflow .
For this reason , liquid returning to the active mud system will contain more fine solids and will eventually require dilution to control fine solids in the mud.
Rope discharge causes incorrect screen selection or broken screen not been changed.
4-4-1- Hydro cyclone Balancing
Hydro cyclone balancing usually done when the mud tanks are full of water , then we open all underflows wide open . Water spins out the bottom . We slowly adjust until the spray becomes a small drip. To achieve these conditions we need the correct pressure.
When all cones adjusted like this they will discharge solids when there are solids in the feed to separate and if no solids , the cones will go back to dripping.
Table 4 resulting mud costs for screen types
Flo divider ensures even liquid and drilled solids distribution to downstream shakers.
Using a flo divider maximizes solids removal capabilities of the shale shakers by ensuring each individual shaker receives an equal distribution of both drilling fluids and drilled solids and eliminates the requirement for a back tank.
4-3- shaker
The continuous liner motion shale shaker system engineered for optimal solids removal .
A high g shaker benefits are:
- increased stoke length
- Increased solids trajectory
- Improved convey rate
- Increased handling capacity
- Increased ability to screen finer and faster
- Improved screen efficiency and screen LIFE.
Maximum flow rate of a screen is directly related to the open area that mud can FLOW THROUGH and the open area that mud can flow through and wire thickness. Two screens with the same openings and with different wire dimension will have different flow CAPACITIES.
The screen with the smaller wire diameter will have a greater flow capacity and also a shorter LIFE.
selection of best screen depends on money , conditions of hole , mud dilution , drilling time and amount of solids in mud .
We use cut point for SCREENS. The phase “d50 cut point is 69 microns “ means that 50% of the 69 microns particles will be rejected and 50 % will pass through the screen or “16d cut point is 49 microns “ means that 16% of the 49 microns particles will be rejected and 84% will pass through the screen .
Derrick screens are manufactured in DX ,PWP < PM and PMD names .
Derrick DX series developed in 1974 and PWP technology developed in 1984.
the screen –life of PWP is longer than DX because PWP has metal backing plate and DX has plastic backing plate.
PMD developed in 1994 by Derrick to increase capacity of screen and PMD+ developed in 1996 . PMD increase the usable screen area to 125% .
The old versions are only able to attend adequate screen life with plastic – backed screen by increasing wire diameters.
Due to the reduced open area from the increase wire diameters, the screen nominal opening must be increased to maintain sufficient capacity . these relatively coarser screens cause solids to increase in the mud system . So, dilution requirement s and mud cost will increase.
Dilution costs can vary dramatically depending which brands of screen are used . for example , for a 9800 HOLE. section of 12-1/4 INCH, hole with a target drilled solids content of 7%, the following dilution expenses could be incurred :
4-4- Hydro cyclone
Hydro cyclone are essential for removing solids on un weighted systems.
Hydro cyclone appear very simple, easy to change part s , and easy to adjust. we need to understand the principles because this allows us to operate the cones efficiently and economically .
Feed slurry fed through the inlet at high velocity obtained by steady pressure of feet head . A centrifugal pump is used to obtain the desired head so, it is important that the pump is sized correctly . The high velocity entering the feed chamber creates a spinning velocity and resulting centrifugal forces and the vortex finder causes the stream to spiral down wards.
Centrifugal force and inertia cause the solids to settle outwards the hydro cyclone wall in a downward stream . As the cone section narrows, the downward spinning liquid moves towards the center and back up the cone . Hydro cyclone cut point is affected by :
- Percent of volume solids in the feed
- Viscosity of the feed fluid
- Size of feed , overflow , and underflow openings
- Inside diameter of Hydro cyclone
- Length Hydro cyclone
A balance design hydro cyclone operate ineffective with rope type underflow discharge.
Rope discharge is the inefficient way to run cones and increase concentration of solid in underflow .
For this reason , liquid returning to the active mud system will contain more fine solids and will eventually require dilution to control fine solids in the mud.
Rope discharge causes incorrect screen selection or broken screen not been changed.
4-4-1- Hydro cyclone Balancing
Hydro cyclone balancing usually done when the mud tanks are full of water , then we open all underflows wide open . Water spins out the bottom . We slowly adjust until the spray becomes a small drip. To achieve these conditions we need the correct pressure.
When all cones adjusted like this they will discharge solids when there are solids in the feed to separate and if no solids , the cones will go back to dripping.
Table 4 resulting mud costs for screen types
| mesh size | cut point (microns) | initial mud (bbls) | dilution required per ft (bbls) | total dilution (bbls) | resulting mud const | |
| demick dx | 210 | 92 | $86 | 0.85 | 8.330 | 716.380 |
| southwest/baroid xr | 210 | 124 | 86 | 1.08 | 10.584 | 910.224 |
| cpi /swaco vmo | 210 | 146 | 86 | 1.035 | 13.230 | 1.137.780 |
If the cones do not discharge clear water in wide open mode , the cyclone is on the dry side of balance . these condition create a dry beach.
Fine solids cannot cross this beach area and they will bridge off by forming a very dry and dense plunge . IT is very difficult to clear plug.
Sometimes solids creates a partially or completely plug in feed inlet . The smooth shape of underflow indicates rotation due to mud entering the feed inlet because partially plug has been occurred .
The straight down flow indicates all mud entering backwards through overflow because completely plug has been occurred .
4-4-2- Hydro cyclone feed header problems
If you make a horizontal bend onto a hydro cyclone header or place a swage less then 3 times pipe diameter in front of a header , some cones operate with rope type and some cone with spray type discharge.
4-4-3- Overflows header problems
Slurp discharge caused by long discharge siphon leg and cured by installing a head siphon breaker .
Hydro cyclone are available with ceramic inserts.
A common method for repairing a leaking cone is using of a high pressure rag.
The ability of hydro cyclone to remove solids from slurry is reduced by:
The word “ decanting means pouring of liquid so slowly that any sediment in the bottom remains undisturbed.
The centrifugal force created by the centrifuge depends on the diameter and Rpm of the bowl. Use the following formula to calculate “ G” force:
G=(RPM)2 (0.0000142) (Diameter of bowl , in )
The performance of centrifuge for a given mud depends on the following factors:
Since in the real world we do not drill spherical balls we use Equivalent Spherical Diameter ( ESD) of the irregular shaped particles . the settling rates of irregularly shaped particles are measured in a liquid with known density and viscosity and ESD can be calculated assuming or knowing the specific gravity of the particles . Two particles of the same ESD but different specific gravities will settle at different rates .
The heavier particle will settle faster .Also ,two particles with different specific gravities will settle at the same rate if their ESD difference compensates . For example , a barite particle (with4.2 SG and 74 microns diameter ) will settle at the same rate as a low specific gravity (2.6 SG and 104 microns diameter ) if its ESD is 1-1/2 times that of the barite particle.
In un weighted muds , the application of centrifuges is solely concerned with drilled solids removal .
Solids removal can be achieved irrespective of how many centrifuges are operated . Centrifuges can be operated in series or in parallel.
In weighted muds, the application of centrifuges is some what different .IN general , two centrifuges are used . One unit is used to remove the weight materials and the second one is used to remove drilled solids . the clean mud is then returned to the achieved system where it is re- united with the recovered weight materials.
In 1970s technology , drive configuration of centrifuge is fixed speed- belt drive . IN this system , one single fixed speed motor drives the bowl and scroll . The speed changing is made by changing pulleys and belts . adjustment requires shut down (approx . 1hour ) and is therefore made in frequently .
In 1980s technology , one electric motor drives the bowl , whilst a second drives a hydraulic pump . A hydraulic motor is used to vary the scroll speed . Adjustment to bowl speed still requires shut down ( approx . 1 hour) and is therefore made importantly . Benefits of variable speed were offset by significantly lower torque capacities
In new technology (1990) , the bowl and scroll can be varied in dependently without shut down .
Benefits of variable speed are offset by significantly lower torque capacities.
In new version of centrifuges , the new effluent ports provide fast precise pond depth settings.
The hydraulic control system of centrifuge including the types of safety system :
1)Automatic feed control
2) Automatic speed boost of scroll to prevent overloading
3) Automatic unit shut down as follows :
- Overheated hydraulic fluid
- Excessive vibration
- Low hydraulic
For example , some characteristics of a hydraulic centrifuge are mentioned below:
Fine solids cannot cross this beach area and they will bridge off by forming a very dry and dense plunge . IT is very difficult to clear plug.
Sometimes solids creates a partially or completely plug in feed inlet . The smooth shape of underflow indicates rotation due to mud entering the feed inlet because partially plug has been occurred .
The straight down flow indicates all mud entering backwards through overflow because completely plug has been occurred .
4-4-2- Hydro cyclone feed header problems
If you make a horizontal bend onto a hydro cyclone header or place a swage less then 3 times pipe diameter in front of a header , some cones operate with rope type and some cone with spray type discharge.
4-4-3- Overflows header problems
Slurp discharge caused by long discharge siphon leg and cured by installing a head siphon breaker .
Hydro cyclone are available with ceramic inserts.
A common method for repairing a leaking cone is using of a high pressure rag.
The ability of hydro cyclone to remove solids from slurry is reduced by:
- Feed head increasing above the recommended range
- increased funnel viscosity
- solids size decreasing
- Overloading the cone with too many solids
- Start the hydro cyclone before the rig pumps and shut down after the rig pumps.
- Make sure all damage screens are changed out immediately (if not this will cause the cones to plug)
- Never by – pass the shakers
- Overload due to fast drilling – open up the under flow beyond the balance point
- When drilling slowly down – close back down to balance point
- Correct operating pressure at manifold equals 4 times mud weigh at 75 fit of correct operation.
The word “ decanting means pouring of liquid so slowly that any sediment in the bottom remains undisturbed.
The centrifugal force created by the centrifuge depends on the diameter and Rpm of the bowl. Use the following formula to calculate “ G” force:
G=(RPM)2 (0.0000142) (Diameter of bowl , in )
The performance of centrifuge for a given mud depends on the following factors:
- The G’ exerted on the fluid
- The retention time of the fluid in the centrifuge
- Conveyor speed
- Bowl diameter
- Length of bowl (increases retention time )
- RPM operating range
- Conveyor speed
- pool depth
Since in the real world we do not drill spherical balls we use Equivalent Spherical Diameter ( ESD) of the irregular shaped particles . the settling rates of irregularly shaped particles are measured in a liquid with known density and viscosity and ESD can be calculated assuming or knowing the specific gravity of the particles . Two particles of the same ESD but different specific gravities will settle at different rates .
The heavier particle will settle faster .Also ,two particles with different specific gravities will settle at the same rate if their ESD difference compensates . For example , a barite particle (with4.2 SG and 74 microns diameter ) will settle at the same rate as a low specific gravity (2.6 SG and 104 microns diameter ) if its ESD is 1-1/2 times that of the barite particle.
In un weighted muds , the application of centrifuges is solely concerned with drilled solids removal .
Solids removal can be achieved irrespective of how many centrifuges are operated . Centrifuges can be operated in series or in parallel.
In weighted muds, the application of centrifuges is some what different .IN general , two centrifuges are used . One unit is used to remove the weight materials and the second one is used to remove drilled solids . the clean mud is then returned to the achieved system where it is re- united with the recovered weight materials.
In 1970s technology , drive configuration of centrifuge is fixed speed- belt drive . IN this system , one single fixed speed motor drives the bowl and scroll . The speed changing is made by changing pulleys and belts . adjustment requires shut down (approx . 1hour ) and is therefore made in frequently .
In 1980s technology , one electric motor drives the bowl , whilst a second drives a hydraulic pump . A hydraulic motor is used to vary the scroll speed . Adjustment to bowl speed still requires shut down ( approx . 1 hour) and is therefore made importantly . Benefits of variable speed were offset by significantly lower torque capacities
In new technology (1990) , the bowl and scroll can be varied in dependently without shut down .
Benefits of variable speed are offset by significantly lower torque capacities.
In new version of centrifuges , the new effluent ports provide fast precise pond depth settings.
The hydraulic control system of centrifuge including the types of safety system :
1)Automatic feed control
2) Automatic speed boost of scroll to prevent overloading
3) Automatic unit shut down as follows :
- Overheated hydraulic fluid
- Excessive vibration
- Low hydraulic
For example , some characteristics of a hydraulic centrifuge are mentioned below:
| bowl size | 14”(mm356) diameter |
| bowl type | contour cylinder |
| conveyor | helical (radial ) axial |
| effluent ports | variable –eccentric |
| differential conveyor speed | 3-90 ram |
| speed rang | 0-400rpm maximum g’s:318 |
| flow rate | 200 gpm with water |
| electrical | 50 hp (37kw)motor 480v. |
| dimensions | length :115”(2921mm) |
| width:75”(1905mm) | |
| weight | |
4-6- Degassing
The main reason that we want to remove gas from the drilling fluids is to keep efficiency of mud pumps.
1)Influx of gas to the well bore due to an under balanced situation (pore pressure greater than hydrostatic , failure keep the hole filled).
2) Drilled gas (porous gas is produce during formation drilling . The amount of gas depends on the drilling rate.
3) Trapped air due to turbulence and drilling fluid properties trapping air .(Water will degas itself but a drilling fluid with a higher viscosity has a greater tendency to trap air ). we can removed a lot of gases will breakout across the shakers , to increase the release of gas . add water in a fine mist apray . Deformers can be added to reduce the surface tension of the bubbles allowing more gas to breakout . Also , we can agitate the pit with a mechanical agitator . This can roll the volume of mud to let the bubbles in the bottom of the pit move upward and breakout .
4-6-1- Mud-Gas separators
The purposes of a mud- gas separator are:
1)Receiving mud from the well
2)Separating the large bubbles from the mud
3) Collecting the mud in the bottom of the separator and allow it to flow to shakers. Flow the separated gas at the top of the separator to a safe place a way from the rig.
Main vent line directs from the choke manifold straight to the flair stack. The separator tank is large enough in diameter and weight to allow for easy separation of gas from mud with an easy flow to the outlet for gas .
Bottom drain in separator tank with a U trap can prevent gas from going to the shakers .
4-6-2- Degassers
We classify degassers in two groups:
Atmospheric degassers and Vacuum Degassers . atmospheric degassers are developed early 1970s . In this degasser , gas- cut mud is pumped into a tank and the mud is sprayed in a thin sheet against the wall of the tank . The impacts are caused separation of mud and gas .
In vacuum degasser , corrugated leaf arrangement promotes superior separation .
It should be mentioned that the more surface area increases the separation .
A Vacuum pump draws mud into the degassing chamber where decreased pressure causes gas bubbles come to surface from the fluid more rapidly.
A stack , corrugated fiberglass leaf arrangement and multiple feed ports provides higher impact , thinner layer of mud dispersion , and greater turbulence for more efficient gas removal.
5- Zero Discharge system
Zero discharge is define d as a process that contains and remediates of acceptable criteria the solids and liquid discharge normally associate with drilling.
Waste materials remediate and control by one or more of the following :
1- subsurface
- injection ( cutting injection technology)
2- Surface
- Isolating (landfill)
- Bio-remediation
- Thermal remediation
- Stabilization
5-1- Dryer
Increasingly strict limitations are placed on the discharge of non-aqueous drilling fluids and their associated drill cutting to the environment.
Dryers are normally utilized to reduce the liquid content of cuttings (specially oil base cuttings) to a level that allows to discharge to the environment.
A drier consists of a vertically configured conical basket centrifuge driven be an electric motor through A planetary gear box.
Wet cutting are fed into the center of the basket and dry cutting exit from the base by gravity .
Effluents are collected in a side holding tank for later solids removal and metering into the active system.
Within the basket is a Tungsten Carbide tiled conveyor that controls the flow of solids over the screen to obtain maximum dryness.
The benefits of a new dryer system are mentioned below:
The technique of injection waste into a casing annual was first done in 1986 by Arco in Alaska.
An Arco rig superintendent injected water based mud down the casing annuli on 3 wells. This led to a substantial interest in this technique, its refinement, and finally its application to the injection of drilled cutting down casing annuli, casing or tubing.
Arco has patented the process of slurrifing drilled cutting with a modified center fugal pump. This modified centrifugal pump is equipment with shortened , specially hardened impeller blades which degrade the cutting to form a slurry . The slurry is then diluted with seawater (and treated with chemical if necessary ) and injected down the chosen casing annuli , casing or tubing and into the pre selected formation sequence.
This technique for the disposal of oil field waste and drilled cutting results in a zero discharge to the environment.
It is the only field proven , cost effective method of disposing of drilling current legislation calls for less than 10 % oil retention on cuttings.
The advantages cutting injection technology is that it offers the operator, opportunity to not only meet current legislation, but also the opportunity to gain the field experience required to meet the upcoming legislation for less than 1% oil retention on cutting or”0” discharge .
This technique of degrading cutting and diluting them to form manageable and pump able slurry opens up various interesting option .
At a single well site , the cutting slurry from the upper hole sections can be pumped to , and stored on a workboat.
When the outer and inner casing string have been set and cemented above and below the injection zone site , the slurry can then be transferred back to the rig for injection.
the environment effects than result from the dumping of drill cutting and the associated drilling fluid are three –fold .
Firstly there is the element of toxicity, secondly there is the element of organic enrichment, and last but possibly the most significant the ”smother effect”.
5-2-1- The cutting injection process and equipment
the cutting injection process starts with the degradation of drilled cutting by mechanical means to form slurry with the appropriate particle size range for injection into the chosen formation sequence . this is followed by the treatment of the cutting slurry by dilution and chemical additions to achieve the require slurry density and theology for injection .
Well in advance of any actual cutting injection operation , the following basic assessment are carried out:
The percentage solids content is a function of the type of formation being drilled and cutting being produced.
The targeted slurry weight for the “17-1/2” and “12-1/4 ” hole sections should be in the range of 11-13 1bs per gallon . The targeted slurry weight for 8-1/2 ”and 6” hole section should be in the range of 11-14 1 bs per gallon .
the slower drilling rates in the 8-1/2 ”and 6” hole section and the reduce volume of cutting at a slightly higher specific gravity will contribute to the potential to generate a higher density slurry for injection.
the funnel viscosity range should be between 50 to 100 sec/qt and can be controlled by volume dilution sea water and if necessary a viscocifier or a thinner can be added .
the cutting injection system proposed is designed to receive the drilled cutting from the rigs solid control equipment , an / or drainage system etc.
Cutting are transported to the slurrification package, via screw conveyors, where they are mixed with water (and chemicals if required ) and via a combination of special mix tank screw agitator and grinding pumps, provide a pump able slurry with predetermined particle distribution for transfer to BHT (Batch Holding Tank).
The slurry is then pumped via a conventional centrifuge gal pump from the BHT to a variable speed triplex injection pump, which injection slurry at a predetermined rate and pressure via the casing annulus into the appropriate injection zone.
The slurry unit is designed with two complete processing system each capable of receiving and grinding cuttings. the bottom of the slurry tanks is conical to minimize settling.
Both tanks are equipment with an optional agitator system.
this system provides an enhanced agitation motion over just relying upon the agitation from the grinding pumps.
perforated baffles are installed inside the slurry tanks to provide additional interference which assists in the overall degradation of the cuttings.
The suction for the grinding pumps is at the base of the tank and thus provides a positive suction at all times.
In addition to the jet lines, which can be operated independently , there is a four inches line which can discharge slurry to the slurry batch holding tank.
the center fugal pump impeller blades are hard faced with tungsten carbide to provide extended life and to cope with the grinding of solids from hard consolidated formations.
All of the piping has been designed to enable each pump to tank suction and discharge into both tanks , as well as being able to back flush the suction line in the event of plugging.
Each batch tank is provided with its own optional agitator, pump, and manifold to allow either to receive the slurry from the slurrification package , and supply the injection pump as and when required .
A bypass line is also provided, whereas the slurry can be discharged directly from the slurrification package to the injection pump.
Classification of the slurry is controlled by circulation the slurry over a shaker.
The main reason that we want to remove gas from the drilling fluids is to keep efficiency of mud pumps.
- Comparing mud weight from a conventional mud seale to a pressurized seals .
- if the mud weight increases after adding water .
- Gas detector warning
- An increasing in viscosity for no apparent reason
- Charging in rheological or chemical properties of the drilling fluid due to chemical reactions
- Appearance of foam in the mud
1)Influx of gas to the well bore due to an under balanced situation (pore pressure greater than hydrostatic , failure keep the hole filled).
2) Drilled gas (porous gas is produce during formation drilling . The amount of gas depends on the drilling rate.
3) Trapped air due to turbulence and drilling fluid properties trapping air .(Water will degas itself but a drilling fluid with a higher viscosity has a greater tendency to trap air ). we can removed a lot of gases will breakout across the shakers , to increase the release of gas . add water in a fine mist apray . Deformers can be added to reduce the surface tension of the bubbles allowing more gas to breakout . Also , we can agitate the pit with a mechanical agitator . This can roll the volume of mud to let the bubbles in the bottom of the pit move upward and breakout .
4-6-1- Mud-Gas separators
The purposes of a mud- gas separator are:
1)Receiving mud from the well
2)Separating the large bubbles from the mud
3) Collecting the mud in the bottom of the separator and allow it to flow to shakers. Flow the separated gas at the top of the separator to a safe place a way from the rig.
Main vent line directs from the choke manifold straight to the flair stack. The separator tank is large enough in diameter and weight to allow for easy separation of gas from mud with an easy flow to the outlet for gas .
Bottom drain in separator tank with a U trap can prevent gas from going to the shakers .
4-6-2- Degassers
We classify degassers in two groups:
Atmospheric degassers and Vacuum Degassers . atmospheric degassers are developed early 1970s . In this degasser , gas- cut mud is pumped into a tank and the mud is sprayed in a thin sheet against the wall of the tank . The impacts are caused separation of mud and gas .
In vacuum degasser , corrugated leaf arrangement promotes superior separation .
It should be mentioned that the more surface area increases the separation .
A Vacuum pump draws mud into the degassing chamber where decreased pressure causes gas bubbles come to surface from the fluid more rapidly.
A stack , corrugated fiberglass leaf arrangement and multiple feed ports provides higher impact , thinner layer of mud dispersion , and greater turbulence for more efficient gas removal.
5- Zero Discharge system
Zero discharge is define d as a process that contains and remediates of acceptable criteria the solids and liquid discharge normally associate with drilling.
Waste materials remediate and control by one or more of the following :
1- subsurface
- injection ( cutting injection technology)
2- Surface
- Isolating (landfill)
- Bio-remediation
- Thermal remediation
- Stabilization
5-1- Dryer
Increasingly strict limitations are placed on the discharge of non-aqueous drilling fluids and their associated drill cutting to the environment.
Dryers are normally utilized to reduce the liquid content of cuttings (specially oil base cuttings) to a level that allows to discharge to the environment.
A drier consists of a vertically configured conical basket centrifuge driven be an electric motor through A planetary gear box.
Wet cutting are fed into the center of the basket and dry cutting exit from the base by gravity .
Effluents are collected in a side holding tank for later solids removal and metering into the active system.
Within the basket is a Tungsten Carbide tiled conveyor that controls the flow of solids over the screen to obtain maximum dryness.
The benefits of a new dryer system are mentioned below:
- Typical waste volume reduction exceeds 30%
- Low power requirement (70HP)
- Low noise – due to V- belt drive
- Reduced footprint
The technique of injection waste into a casing annual was first done in 1986 by Arco in Alaska.
An Arco rig superintendent injected water based mud down the casing annuli on 3 wells. This led to a substantial interest in this technique, its refinement, and finally its application to the injection of drilled cutting down casing annuli, casing or tubing.
Arco has patented the process of slurrifing drilled cutting with a modified center fugal pump. This modified centrifugal pump is equipment with shortened , specially hardened impeller blades which degrade the cutting to form a slurry . The slurry is then diluted with seawater (and treated with chemical if necessary ) and injected down the chosen casing annuli , casing or tubing and into the pre selected formation sequence.
This technique for the disposal of oil field waste and drilled cutting results in a zero discharge to the environment.
It is the only field proven , cost effective method of disposing of drilling current legislation calls for less than 10 % oil retention on cuttings.
The advantages cutting injection technology is that it offers the operator, opportunity to not only meet current legislation, but also the opportunity to gain the field experience required to meet the upcoming legislation for less than 1% oil retention on cutting or”0” discharge .
This technique of degrading cutting and diluting them to form manageable and pump able slurry opens up various interesting option .
At a single well site , the cutting slurry from the upper hole sections can be pumped to , and stored on a workboat.
When the outer and inner casing string have been set and cemented above and below the injection zone site , the slurry can then be transferred back to the rig for injection.
the environment effects than result from the dumping of drill cutting and the associated drilling fluid are three –fold .
Firstly there is the element of toxicity, secondly there is the element of organic enrichment, and last but possibly the most significant the ”smother effect”.
5-2-1- The cutting injection process and equipment
the cutting injection process starts with the degradation of drilled cutting by mechanical means to form slurry with the appropriate particle size range for injection into the chosen formation sequence . this is followed by the treatment of the cutting slurry by dilution and chemical additions to achieve the require slurry density and theology for injection .
Well in advance of any actual cutting injection operation , the following basic assessment are carried out:
- selection of a suitable formation to inject the cutting slurry into, porous and permeable or potentially permeable with the application of hydraulic pressure.
- Cement, casing and wellhead design to accommodate the anticipated pressure required to inject the cutting slurry into the appropriate formation.
- Evaluation of injection pump pressured and pumps capacity requirements.
- Evaluation of available desk space, desk loading limits and power consumption to support the cutting injection package at the rig site.
The percentage solids content is a function of the type of formation being drilled and cutting being produced.
The targeted slurry weight for the “17-1/2” and “12-1/4 ” hole sections should be in the range of 11-13 1bs per gallon . The targeted slurry weight for 8-1/2 ”and 6” hole section should be in the range of 11-14 1 bs per gallon .
the slower drilling rates in the 8-1/2 ”and 6” hole section and the reduce volume of cutting at a slightly higher specific gravity will contribute to the potential to generate a higher density slurry for injection.
the funnel viscosity range should be between 50 to 100 sec/qt and can be controlled by volume dilution sea water and if necessary a viscocifier or a thinner can be added .
the cutting injection system proposed is designed to receive the drilled cutting from the rigs solid control equipment , an / or drainage system etc.
Cutting are transported to the slurrification package, via screw conveyors, where they are mixed with water (and chemicals if required ) and via a combination of special mix tank screw agitator and grinding pumps, provide a pump able slurry with predetermined particle distribution for transfer to BHT (Batch Holding Tank).
The slurry is then pumped via a conventional centrifuge gal pump from the BHT to a variable speed triplex injection pump, which injection slurry at a predetermined rate and pressure via the casing annulus into the appropriate injection zone.
The slurry unit is designed with two complete processing system each capable of receiving and grinding cuttings. the bottom of the slurry tanks is conical to minimize settling.
Both tanks are equipment with an optional agitator system.
this system provides an enhanced agitation motion over just relying upon the agitation from the grinding pumps.
perforated baffles are installed inside the slurry tanks to provide additional interference which assists in the overall degradation of the cuttings.
The suction for the grinding pumps is at the base of the tank and thus provides a positive suction at all times.
In addition to the jet lines, which can be operated independently , there is a four inches line which can discharge slurry to the slurry batch holding tank.
the center fugal pump impeller blades are hard faced with tungsten carbide to provide extended life and to cope with the grinding of solids from hard consolidated formations.
All of the piping has been designed to enable each pump to tank suction and discharge into both tanks , as well as being able to back flush the suction line in the event of plugging.
Each batch tank is provided with its own optional agitator, pump, and manifold to allow either to receive the slurry from the slurrification package , and supply the injection pump as and when required .
A bypass line is also provided, whereas the slurry can be discharged directly from the slurrification package to the injection pump.
Classification of the slurry is controlled by circulation the slurry over a shaker.
