Kashagan oil field has been under production since September 2016. The produced oil is associated with considerable amounts of sour gas that must be processed or disposed of while minimizing flaring. This paper will focus on the methodology for field development planning and production forecasting, incorporating gas reinjection and sulphur management with the objective of optimizing production, subject to operational constraints and bottlenecks at surface facilities.
The field development plan includes reinjection of associated gas into the reservoir to increase oil production capacity at the surface and provide reservoir pressure support, while satisfying government regulations that do not allow continuous gas flaring. This requires analysis of H2S concentration and sulphur production, since the ultimate surface constraint at Kashagan field is sulphur processing capacity.
We describe reservoir modeling workflows for oil production optimization with integrated logic for gas balancing. The impact of sulphur management on oil production is studied under different scenarios using a high resolution, fully compositional reservoir model.
The procedures for management of the production facilities have been translated into reservoir simulation logic, including product streaming from facilities and processing constraints. This includes gas accounting and prioritization of gas with low H2S content to be processed at the sulphur recovery unit. The remaining gas with higher H2S content is sent back to the injection stream.
Workflows have been developed using tailored scripting with user-friendly input of facilities constraints using spreadsheets to enable the model to be maintained in a ‘live’ state. Automatic allocation methods are used for prediction forecasting that penalize higher gas production wells but still provide incremental oil production. Development of a product streaming model allows for reporting of production of liquefied petroleum gas (LPG), dew-pointed gas, etc., in addition to the standard simulation results.
The comprehensive guidelines provided in this paper can aid reservoir modeling and surveillance for a field through accurate analysis of actual operational constraints and bottlenecks as part of the planning process. The described gas and sulphur management logic provide pivotal information to enable the reservoir engineering and production teams to meet the challenges of development planning for a sour reservoir.