A Research Of EOR By Hydrocarbon Gas Injection In JAKE-S Oilfield

Recent years, with domestic and foreign gas injection technology developed rapidly, gas injection type, gas injection method, gas injection occasion, suitable for gas injection reservoir continuous developed, the gas injection technology has become the rapid development of enhanced oil recovery in addition to thermal method. At present, the gas injection as an effective enhanced oil recovery method in the world has been widely used. Gas injection technology is quite mature in the USA and Canada. In the USA, the gas injection EOR is dominated by CO2miscible phase, while in Canada, the industrial miscible phase drive is dominated by injection of hydrocarbon solvents. The gas injection technology in China is relatively slow pace of development, but in recent decades, has also carried out a lot of indoor gas drive experimental research and field pilot test. Gas injection enhanced oil recovery technology, depending on the injected gas type can be divided into the hydrocarbon flooding and flooding of non-hydrocarbon. Hydrocarbon drive is that a lighter hydrocarbon gas is injected into the reservoir to enhance oil recovery method. In this paper, we mainly research hydrocarbon gas injection to enhance oil recovery in Sudan JAKE-S oilfield. We have studied JAKE-S reservoir geology and reservoir fluid characteristics, the phase characteristics of the formation fluid, gas injection and formation fluids miscible pressure, based on these combined with numerical reservoir simulation studied post-development programs in JAKE-S oilfield, finally set of on-site implementation of the recommended programs, which provide technical support for the JAKE-S oilfield for EOR.Jake South Oilfield is located in the southeast of the Fula depression. Fula depression represents strike of SN with Fula East fault being east boundary and controlled by Fula West fault in the west.5secondary structure zones of "3-positive2-negative" of south fault terrace zone, south secondary depression, middle structural zone, north secondary depression and north fault terrace zone are developed from WS to NE, distributed in diagonal manner. Jake South structure is located in the south of the Jake3D survey and is fault anticline structure cut by cluster of small faults with strike of WN. The early Jurassic strata are complete and discovered and overall, it is cut with cluster of small faults from WN to ES and the pattern of structure is not damaged. Bentiu is the goal of this research, which is the main reservoir of JAKE-S oilfield. The reservoir of Bentiu formation of Fula North fault block is a massive reservoir of fault anticline on horst block with strong bottom water,3.9km2of the closed area, closed height of170m, cut to three blocks by the fault. This paper studies the following:First of all, on the basis of the reservoir information in the Sudan JAKE-S oilfield, the reservoir geological characteristics, reservoir temperature, pressure, fluid properties and rock characteristics were analyzed and evaluated; reservoir geological reserves were calculated and evaluated; the natural reservoir energy were evaluated. Base on the domestic and foreign literature research, we studied the gas injection EOR technology status, analyzed the domestic and foreign typical cases, studied gas injection EOR technology screening criteria. Base on these, we studied gas injection EOR technology in Jake-S reservoir.Secondly, based on reservoir fluid PVT experimental data, we used Canada’s CMG-Winprop phase simulation software to match the saturation pressure of the reservoir fluids and single time flash vaporization, expansion experiments for constant composition, differential degassing experiment, then, analyzed the phase behavior of fluids, but also, provided data for the parameter field of the fluid physical property catering for the study on numerical simulation of gas injection drive reservoir and the preparation for the development plan. On the basis of reservoir fluid phase matching, we used the empirical formula method, simulation method of slim-tube experiment and triangular phase diagrams to study MMP between dry gas or condensate gas and reservoir fluids.Finally, we matched history production of region and single well on the basis of the reservoir geological model, and analyzed the remaining oil distribution features. At last, we studied hydrocarbon gas injection post-development program of Jake-S reservoir, finally designed the recommended programs used in field.The innovation of this。paper is:pseudo-component division of reservoir fluid and match of fluid phase behavior; using a variety of ways to study MMP; optimizing the post-development program combining reservoir characteristics and the influence of many factors.By studying hydrocarbon gas injection EOR in JAKE-S oilfield, we get the following conclusions:①Jake-S reservoir has a normal temperature, pressure system, middle porosity and high permeability, good physical properties; reservoir fluid has low-density, low viscosity; reservoir has a strong side and bottom water, sufficient natural energy in the early.②Integrating case study worldwide and gas injection EOR technology screening criteria, development of Jake-S reservoir should use a mode that combines gas injection and WAG injection to enhance oil recovery.③From the results of the studying of reservoir fluid phase behavior and fluid phase matching, we know that the results of PVT experimental fluid phase matching is good, the matching accuracy is high, which provided data for the parameter field of the fluid physical property catering for the study on numerical simulation of gas injection drive reservoir and the preparation for the development plan. P-T diagram produced by the experimental phase matching results show that the reservoir is a medium black oil reservoir.④It can be discovered from the results of studying MMP that when lean gas is injected, the MMP of Jake-S reservoir is about30MPa and it’s difficult to form miscible phase. But if the gas condensate is injected, the MMP is just about20MPa. During gas injection, the pressure of near wellbore is fairly high and it is expected to achieve miscible phase or near-miscible phase.⑤Through the analysis of numerical reservoir simulation, the simulation area recovery factor is low; there are still a lot of surplus reserves underground. The main parts of high remaining reserves abundance is in the reservoir central area. For the periphery of the reservoir area, the remaining reserves abundance is low due to the effect of edge water.⑥About injection method, the best way is to combine gas injection in up part wells and WAG injection in low part wells. Water alternating gas injection in low part wells can digest part of produced sewage, and it can also decrease field total gas injection, featuring sound technical, economic and environmental benefits.⑦Considering injectivity and equipment condition of the field, a greater injection rate can guarantee a better development performance. At the same time a higher injection pressure is good to miscibility.⑧As to selection of injection gas, we suggest injecting gas condensate from AG layer directly into Bentiu layer to make injection gas and crude oil reach a miscible phase or a near miscible phase to get a higher crude oil recovery.⑨ecommended implementation plan of Jake-S reservoir gas injection is as follows:drill four new oil wells, then gas injection in3upper part wells, WAG injection in4lower part wells with initial off-take rate of10%. It is better to try to ensure that gas condensate from AG layer to be injected back to Bentiu layer, it is predicted that crude oil recovery ratio can amount to70%approximately.