Designing Optimum Salinity and Injection Rates for Low Salinity Water Alternating Hydrocarbon Gas Injection at “B” Structure in “S” Field

Abstrak

The inability of primary and secondary recovery methods in maximizing oil recovery from existing fields and the lack of new major reserve discoveries have been the two main issues in the oil and gas industry these days. The best solution to solve both problems is by performing enhanced oil recovery (EOR). One of the recent EOR methods that have been developed by many researchers is low salinity water alternating gas (LSWAG) injection. In the LSWAG injection, the type of injection gas that is preferred to be used is hydrocarbon gas. However, there are still limited studies that discuss the implementation of low salinity water alternating hydrocarbon gas injection in prospective fields along with its possible mechanisms.

This study is conducted to design the low salinity water alternating hydrocarbon gas injection at a sandstone reservoir named "B" Structure in "S" Field, Indonesia. Injected water salinity, water injection rate, and gas injection rate are the parameters that become the focus of this study. Sensitivity study through reservoir simulation using a compositional simulator, CMG GEM^TM, is performed to study the impact of these parameters on oil recovery by evaluating reservoir dynamic properties and to determine the optimum scenario.

The results of this study conclude that oil recovery increases as the injected water salinity decreases due to wettability alteration towards more water wet. On the other hand, oil recovery increases as the water injection rate and gas injection rate increase due to sweep efficiency improvement. The optimum design of the LSWAG injection, after considering the capacities of field facilities, yields a significant increase of recovery factor from base case. Moreover, this advanced method can reduce cost and gas emission as it utilizes the produced gas.