Experimental Investigation on EOR and Flowback Rate of UsingSupercritical CO2 as Pre-Fracturing Fluid in Tight Oil Reservoir

摘要

Fracturing is the necessary means of tight oil development and the most common fracturing fluid isslickwater. However, the loess plateau of ordos basin in China is seriously short of water resources.Therefore, the tight oil development in this area by hydraulic fracturing is extremely expensive and badfor the environment. In this paper, a new method using CO2 as pre-fracturing fluid is applied in hydraulicfracturing. This method can give full play to the dual advantages of supercritical CO2 characteristics andmixed water fracturing technology while saving water resources at the same time. On the other hand, thismethod can reduce reservoir damage, change rock microstructure, and significantly increase oil productionafter full interaction with formation fluid, which is a development method with broad application prospect. In this work, the main mechanism, the the system energy enhancement, and flowback rate of CO2 aspre-fracturing fluid are investigated. Firstly, the microscopic mechanism of CO2 fracturing was studied,and the effects of CO2 on pores and rock minerals were analyzed by NMR test, XRD analysis andSEM experiment. Secondly, the high pressure chamber reaction experiment was conducted to study thedistribution and existence state of supercritical CO2 in the multiphase fluid during the full-cycle fracturingprocess. Finally, four injection modes of CO2 injection experiments were designed to compare the pressureincrease, production enhancement, and flowback rate of CO2 and slickwater, so as to optimize the optimalCO2 injection mode and the optimal injection amount of CO2 slug.