Key geological factors controlling oil displacement efficiency of CO2 injection in low-permeability reservoirs

Zhaosheng Wang,Lianbo Zeng,Zhenguo Zhang,Jiangtao Yu,Yuncheng Liu,Siyu Yang

doi:10.1177/0144598721995609

Abstract

Carbon dioxide (CO2) flooding is an effective method to enhance oil recovery in low-permeability reservoirs. Studying key geological factors controlling oil displacement efficiency is of great significance to the CO2 injection scheme design in low-permeability reservoirs. Focusing on low-permeable H reservoir in Songliao Basin, China, this paper describes the contact and connection of sand bodies, natural fractures and high-permeability zones with core samples, log data and experiment firstly. After that, the impact of interaction of sand body connection, natural fracture and high-permeability zone on oil displacement efficiency is determined by using geological and dynamic data in CO2 injection area. Results indicate that the connection of single sand bodies between injectors and producters wells primarily controls CO2 flooding in low-permeability reservoirs. Furthermore, coupling of sand body connection, natural fractures and high-permeability zones is the key geological factor governing oil displacement efficiency of CO2 injection in low-permeability reservoirs, where well or generally-connected sand bodies can improve the efficiency significantly. Meanwhile, the dominant seepage channels in other directions have no influence on producers, which is beneficial to improve CO2 flooding efficiency.

Highlights

It is generally known that crude oil is important fossil fuel providing energy for continued economic and social progress worldwide (Du et al, 2018)
The sand body can be categorized into two microfacies: subaquatic distributary channel and mouth bar, which are assumed to be strip-shaped and sheet-shaped, respectively
The sand bodies in mouth bar are contacted in three patterns, bar bodies are well-connected, followed by bar body and bar edge, while the bar edges are poorly-connected (Figure 5(b))

Summary

Introduction

It is generally known that crude oil is important fossil fuel providing energy for continued economic and social progress worldwide (Du et al, 2018). With significant demand for oil and gas resources, low-permeable reservoirs (matrix permeability less than 50 Â 10À3 mm2), which are widely distributed and are rich in oil and gas resources (Hu, 2009), play an important role in oil and gas development in China Water injection it is regarded as a high-cost and low efficiency approach to develop these reservoirs because of strong heterogeneity. Oil displacement with CO2 injection is characterized by low pressure and strong suction capacity in low-permeability reservoir, which is to keep balance between injectors and producers with no reservoir damage (Dedy et al, 2020) It can reduce negative effect of capillary force and enhance oil displacement efficiency using miscible or semi miscible CO2 flooding (Choubineh et al, 2016; Stephenson et al, 1993; Zhao and Liao, 2012). Using CO2 injection to enhance oil recovery in low-permeability reservoir has attracted considerable attention from geologists and petroleum engineers (Saira et al, 2020; Sridhara et al, 2018; Wang et al, 2014)

Methods

Results

Conclusion