Abstract
The complex fault block reservoir has the characteristics of small area and many layers in vertical. Due to the influence of formation heterogeneity and well pattern, the situation that “water fingering is serious with water injection, on the contrary, driving energy is low” frequently occurs in water flooding, which makes it difficult to enhance oil recovery. Asynchronous injection-production (AIP) process divides the conventional continuous injection-production process into two independent processes: injection stage and production stage. In order to study oil recovery in the fault block reservoir by AIP technology, a triangle closed block reservoir is divided into 7 subareas. The result of numerical simulation indicates that all subareas have the characteristic of fluid diverting and remaining oil in the central area is also affected by injected water at injection stage of AIP technology. Remaining oil in the central area is driven to the included angle and border area by injected water and then produced at the production stage. Finally, the oil recovery in the central area rises by 5.2% and in the noncentral area is also increased in different levels. The AIP process can realize the alternative change of reservoir pressure, change the distribution of flow field, and enlarge the swept area by injected water. To sum it up, the AIP process is an effective method to improve the oil recovery in complex fault-block reservoir by water flooding.
Highlights
Due to the fault cutting, the complex fault block reservoir has characteristics of breaking block, numerous fault blocks, complicated structures, and complicated oil-water relationship [1,2,3]. e effect of water flooding is affected by the reservoir area, reservoir structure, and well pattern in complex fault block reservoirs
Arab et al studied the water flooding mechanism of the heavy oil reservoir based on the experimental results of heavy oil water flooding and the results showed that low injection rate can greatly improve oil recovery [4]
Cheng et al aimed to optimize the scale of the stimulated reservoir volume (SRV) by conducting an experiment to verify the water injection capacity of the Chang 7 Formation, which is situated within a typical tight oilfield [5]
Summary
Due to the fault cutting, the complex fault block reservoir has characteristics of breaking block, numerous fault blocks, complicated structures, and complicated oil-water relationship [1,2,3]. e effect of water flooding is affected by the reservoir area, reservoir structure, and well pattern in complex fault block reservoirs. In about 0.1 km area of complex fault block reservoirs, the production contradiction that “if water injection is not applied, reservoir pressure is low, else the producer with high water cut” is serious. AIP is a potential technology to improve oil recovery by alternative opening of the injector and producer to change the distribution of pressure and fluid saturation in the reservoir. E contributions of this paper lie in two aspects: (1) the subareas of the complex fault block reservoir are studied and the mechanism of AIP in different subareas is discussed; (2) the changes of pressure, oil saturation, and fluid flow direction are studied in the subareas by AIP, and the sweep efficiency, oil displacement efficiency, and recovery are compared with conventional water flooding for further comparative study.
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