Compatibility characteristics of fracturing fluid and shale oil reservoir: A case study of the first member of Qingshankou Formation, northern Songliao Basin, Northeast China

Abstract

Hydraulic fracturing is currently one of the most economical and effective means to develop shale oil resources. However, the fracturing effects in shale oil wells vary significantly. The compatibility between the fracturing fluid and the shale oil reservoir is one of the important factors affecting the fracturing stimulation. In this study, a series of physical simulation experiments were carried out to reveal the changes in the physical properties and surface properties of a shale oil reservoir using different fracturing fluids (guar gum fracturing fluid, slick hydraulic fracturing fluid, and formation water fracturing fluid). The dynamic flowback process of different fracturing fluids was visualized and quantitatively characterized using the NMR technology. The results indicate that with the increase in soaking time in the formation water fracturing fluid, the hysteresis coefficient of the shale increased. The increasing ink-bottle pores resulted in worse pore connectivity and physical properties of reservoir. The shale undergoes strong water sensitivity damage and strong stress sensitivity, which is not conducive to the stability and long-term effects of shale oil production. After injecting the guar gum fracturing fluid, the pore connectivity of the shale is enhanced, and the stress sensitivity is the weakest. The particle suspension and dispersion system of the guar gum fracturing fluid is the most stable, which greatly avoids reservoir damage caused by solid particle migration blocking in the pore throat. In addition, it can effectively inhibit shale hydration and expansion, and achieve the highest displacement flowback efficiency, which is more suitable for the fracturing operation of shale oil reservoirs in the study area. The effects of the slippery hydraulic fracturing fluid on shale are between the above two fracturing fluids. The research results are of great significance in guiding the fracturing operation of shale oil wells in the northern Songliao Basin.