Designing Optimum Salinity, Cycle, and Gas-Water Ratio of Low Salinity Water Alternating Hydrocarbon Gas Injection at “B” Structure in “S” Field
Abstrak
In the last decades, injection of brines with modified ionic composition has been developed to improve oil recovery. low salinity water injection (LSWI) is one of the most prominent enhanced oil recovery (EOR) method which can increase oil recovery better than that other conventional chemical EOR methods. As a result of further studies of LSWI, an idea of combining it with other EOR technique was generated. One of the idea is to combine LSWI with gas injection which is known as low salinity water alternating gas (LSWAG) injection. Applying water alternating gas (WAG) in LSWI process means to inject both low salinity water and gas to the reservoir in order to improve the oil recovery. The presence of flue gas produced during production process leads to the idea of utilizing the produced hydrocarbon gas to be used for injection as pure carbon dioxide (CO2) gas is considered costly.
In this study, the author proposes the idea of modelling low salinity water alternating hydrocarbon gas (HydrocarbonLSWAG) injection using compositional model to identify the effects of Hydrocarbon-LSWAG injection operational parameters and to propose the most optimum HydrocarbonLSWAG injection scenario to be applied in the sandstone reservoir at “B” Structure in “S” Field, South Sumatera Province, Indonesia. Reservoir simulations and production forecasts were done using CMG GEM Simulator during 15 years of production period starting from 1 TM January 2021 until 1 st January 2036 with preliminary work using CMG WINPROP st for generating the reservoir fluid compositional model. Series of sensitivity analysis were conducted in this study to identify the effects of operational parameters in modelling Hydrocarbon-LSWAG injection and to determine the most optimum Hydrocarbon-LSWAG injection scenario to be applied at “B” Structure in “S” Field to gain promising oil recovery using two injector wells. Water salinity, number of cycle and gas-water injection duration ratio were varied in order to observe the effects of those parameters to oil recovery factor.
The results of this study show that injection using lower water salinity of 1,800 ppm results in higher oil recovery compared to water salinity of 3,600 ppm. The findings of this study also show that the increasing number of Hydrocarbon-LSWAG injection cycle is neither directly or inversely proportional to the improvement of oil recovery. Furthermore, the resulted recovery factor is higher when the LSWI duration is longer than the hydrocarbon gas injection, in this case, with 1:2 ratio of gas-water injection. The most optimum Hydrocarbon-LSWAG scenario to be applied in “B” Structure of “S” Field is by injecting hydrocarbon gas of 0.25 MMSCFD alternating with low salinity water injection of 1000 BPD with injected water salinity of 1,800 ppm by applying one Hydrocarbon-LSWAG injection cycle for each year with gas-water injection duration ratio of 1:2 which results in 60.01% of oil recovery factor. Therefore, Hydrocarbon-LSWAG is suggested to be applied in “B” Structure of “S” Field for further field development.
