An Approach to Miscible Injection in the Oil Rim Reservoir

Across PJSC «Gazprom Neft» portfolio of technological projects an especial place is reserved for gas technologies and miscible flooding is one of them. It allows to increase production and recovery factor but also helps utilize rich gas components which otherwise would be flamed/sold without extra value. This paper discusses development options of miscible injection in oil rim reservoir.

To evaluate gas processing options multiple models in Aspen HYSYS were designed in order to increase extraction of C2–C4 fraction that is mixed with lean gas to achieve miscible displacement in the reservoir, since otherwise the only option to get rid of C2–C4 is to mix in with lean gas and sell as pipeline gas. At the beginning PVT model was designed and MME was evaluated. Having results from actual lab experiments and compositional modeling software available optimal composition of injection fluids and pressure regimes were investigated. Current and planned patterns of oilfields were studied for best injector location using 3D compositional simulator. Integrated models were built to monitor and predict produced and injected gas compositions and volumes. In addition they allowed watching for bottle-necks in production network, cryogenic plant, gas facilities and calculation of recycling volume.

Main idea was to ensure maximum economically possible extraction of C2–C4 fraction from produced gas thus obtaining fluid for miscible injection. During iterative process decision was to be made between -55 and -80O C after turbo-expander and the last one was more prominent, since it increased extraction by 35%. According to MME test, average pressure, regimes of production and available volume of gas optimal composition of miscible gas is 65% methane and is achieved by mixing C2–C4 with lean gas for a pipeline and gas cap injection. Gas utilization achieves maximum for patterns with higher OIP, number of wells and their density. WAG is considered to perform better in terms of gas utilization that in its turn leads to increased incremental oil. By choosing most efficient patterns in terms it became possible to increase recovery in these regions by 10–15%.

The paper describes the approach used to design development strategy of miscible flooding option for the oil rim reservoir. Technical details shown describe cryogenic plant design considerations, selection process of optimal injected gas composition, evolution of development strategy for the reservoir. The approach shows a way to incorporate all available data into one decision-making space in order to achieve maximum value from available resources.