Gathering Systems
Raw crude produced from individual production wells located at well pads is diverted to manifolds. The system that collects and transfer the fluid to the place for processing is normally called Gathering System. In this section we will describe how NoDoCmodels the cost simulation for gathering systems and manifolds for oil & gas both on onshore and offshore. Followings are considerd as the NoDoC models basis.
As mentioned, crude oil and natural gas are gathered from wells and flows to a header with name of manifolds. Also most crude oil and natural gas production requires some treatment to remove undesirable components before the commodity goes to market.TREATMENT FACILITIES can range from settling tanks that remove sediment and water, to billion-dollar plants that remove sour (hydrogen sulphide [H2S]) gas, carbon dioxide, nitrogen and water, and separate out major products, including condensate, natural gas liquids (NGLs) and sulphur. Gas-gathering and transmission lines are required to transport raw gas to processing plants and marketable gas to other transmission lines and customers. Crude oil and NGLs are collected by main gathering systems and transported to refineries for processing.
The duty of gathering systems are:
- Collecting gas from wells and sending to central facilities and gas processing plants
- Collecting oil from wells
- Including separators and treaters to remove gas and water from oil at well site or central battery
- Collecting and transporting of oil to refineries via main gathering systems and transmission lines
- INSTALLING line heater or dehydrators at wells to prevent freezing and condensation during transport
NoDoC models gathering systems according to the oil & gas technical parameters. The oil or gas may be sour and then based on the rating that they have, the NoDoC model guide the user step by step to accept the model recommendations or input his own data.
In particular, a gas gathering network can become very large, with production from hundreds of wells, several hundred kilometers/miles apart, feeding through a gathering network into a processing plant.
For the smallest reservoirs, oil is simply collected in a holding tank and collected at regular intervals by tanker truck or railcar to be processed at a refinery.
In Onshore, The individual well streams are brought into the main production facilities over a network of gathering pipelines and manifold systems. The purpose of these is to allow set up of production “well sets” so that for a given production level, the best reservoir utilization, well flow composition (gas, oil, waster) etc. can be selected from the available wells.
For gas gathering systems, it is common to meter the individual gathering lines into the manifold. For multiphase (combination of gas, oil and water) flows, the high cost of multiphase FLOW METERS often lead to the use of software flow rate estimators that use well test data to calculate the actual flow.
In Offshore, the dry completion wells on the main field centre feed directly into production manifolds, while outlying wellhead towers and subsea INSTALLATIONS feed via multiphase pipelines back to the production risers. Risers are the systems that allow a pipeline to “rise” up to the topside structure. For floating or structures, this involves a way to take up weight and movement. For heavy crude and in arctic areas, diluents and heating may be needed to reduce viscosity and allow flow.
Costs for gathering system and related facilities associated with the oil fields, to collect oil from existing wells, process the oil to remove gas and water and transfer the oil to a refinery or for storage are estimated millions of Dollars, depend on the number of wells, flow rate of the fluid, and many other technical parameters.
To simulate the cost estimates for the gathering systems, NoDoC have developed a model for the equipment requirements and configurations for fields and wells using the following parameters as estimation basis.
The flow lines may include several check valves. The choke, master and wing valves are relatively SLOW, therefore in case of production shutdown, pressure before the first closed sectioning valve will rise to the maximum wellhead pressure before these valves can close. The pipelines and risers are designed with this in mind.
Short pipeline distances is not a problem, but longer distances may cause multiphase well flow to separate and form severe slugs, plugs of liquid with gas in between, traveling in the pipeline. Severe slugging may upset the separation process, and also cause overpressure safety shutdowns. Slugging might also occur in the well as described earlier. Slugging may be controlled manually by adjusting the choke, or with automatic slug controls. Further, areas of heavy condensate might form in the pipelines. At high pressure, these plugs may freeze at normal sea temperature, e.g. if production is shut down or with long offsets. This may be prevented by injecting ethylene glycol. The main parameters for estimation are:
- The equipment configurations the nominated fields,
- The wells configuration,
- Distance between wells,
- Distance between wells and manifold(s),
- Flow rate of fluids from the wells,
- Composition of the fluids,
- Pressure and temperature of the fluids from the each well,
- Well ratings
As mentioned, crude oil and natural gas are gathered from wells and flows to a header with name of manifolds. Also most crude oil and natural gas production requires some treatment to remove undesirable components before the commodity goes to market.TREATMENT FACILITIES can range from settling tanks that remove sediment and water, to billion-dollar plants that remove sour (hydrogen sulphide [H2S]) gas, carbon dioxide, nitrogen and water, and separate out major products, including condensate, natural gas liquids (NGLs) and sulphur. Gas-gathering and transmission lines are required to transport raw gas to processing plants and marketable gas to other transmission lines and customers. Crude oil and NGLs are collected by main gathering systems and transported to refineries for processing.
The duty of gathering systems are:
- Collecting gas from wells and sending to central facilities and gas processing plants
- Collecting oil from wells
- Including separators and treaters to remove gas and water from oil at well site or central battery
- Collecting and transporting of oil to refineries via main gathering systems and transmission lines
- INSTALLING line heater or dehydrators at wells to prevent freezing and condensation during transport
NoDoC models gathering systems according to the oil & gas technical parameters. The oil or gas may be sour and then based on the rating that they have, the NoDoC model guide the user step by step to accept the model recommendations or input his own data.
In particular, a gas gathering network can become very large, with production from hundreds of wells, several hundred kilometers/miles apart, feeding through a gathering network into a processing plant.
For the smallest reservoirs, oil is simply collected in a holding tank and collected at regular intervals by tanker truck or railcar to be processed at a refinery.
In Onshore, The individual well streams are brought into the main production facilities over a network of gathering pipelines and manifold systems. The purpose of these is to allow set up of production “well sets” so that for a given production level, the best reservoir utilization, well flow composition (gas, oil, waster) etc. can be selected from the available wells.
For gas gathering systems, it is common to meter the individual gathering lines into the manifold. For multiphase (combination of gas, oil and water) flows, the high cost of multiphase FLOW METERS often lead to the use of software flow rate estimators that use well test data to calculate the actual flow.
In Offshore, the dry completion wells on the main field centre feed directly into production manifolds, while outlying wellhead towers and subsea INSTALLATIONS feed via multiphase pipelines back to the production risers. Risers are the systems that allow a pipeline to “rise” up to the topside structure. For floating or structures, this involves a way to take up weight and movement. For heavy crude and in arctic areas, diluents and heating may be needed to reduce viscosity and allow flow.
Costs for gathering system and related facilities associated with the oil fields, to collect oil from existing wells, process the oil to remove gas and water and transfer the oil to a refinery or for storage are estimated millions of Dollars, depend on the number of wells, flow rate of the fluid, and many other technical parameters.
To simulate the cost estimates for the gathering systems, NoDoC have developed a model for the equipment requirements and configurations for fields and wells using the following parameters as estimation basis.
The flow lines may include several check valves. The choke, master and wing valves are relatively SLOW, therefore in case of production shutdown, pressure before the first closed sectioning valve will rise to the maximum wellhead pressure before these valves can close. The pipelines and risers are designed with this in mind.
Short pipeline distances is not a problem, but longer distances may cause multiphase well flow to separate and form severe slugs, plugs of liquid with gas in between, traveling in the pipeline. Severe slugging may upset the separation process, and also cause overpressure safety shutdowns. Slugging might also occur in the well as described earlier. Slugging may be controlled manually by adjusting the choke, or with automatic slug controls. Further, areas of heavy condensate might form in the pipelines. At high pressure, these plugs may freeze at normal sea temperature, e.g. if production is shut down or with long offsets. This may be prevented by injecting ethylene glycol. The main parameters for estimation are:
- The equipment configurations the nominated fields,
- The wells configuration,
- Distance between wells,
- Distance between wells and manifold(s),
- Flow rate of fluids from the wells,
- Composition of the fluids,
- Pressure and temperature of the fluids from the each well,
- Well ratings
