The Effect of Fracture Aperture on Fracturing Fluid Imbibition into Gas-Saturated Rocks

Abstract

ABSTRACT: During well shut in after hydraulic fracturing, a large amount of fracturing fluid enters the formation through imbibition, which significantly reduces the recovery of injected water. However, the capillary pressure of fractures is usually ignored, and the effect of fracture aperture on this process is not clear. We examined the imbibition characteristics between fractures and matrix in the capillary-controlled gas-water flow. The focus is on the flow behavior and effects caused by capillary pressure of fractures. The imbibition experiments were carried out under different fracture apertures (50-950 μm). The results show that fractures within a certain opening range accelerate water imbibition by providing a plane source. The water flows rapidly in the fractures, then being absorbed by the matrix on both sides. The water imbibition rate of fractures is mainly affected by the fractures aperture, which controls the fracture capillary pressure and permeability. The overall trend is that the imbibition rate is inversely proportional to the fracture aperture. This indicates that the small aperture fractures without proppants can quickly transport water to the interior of the matrix. The research is significant to understand the law of fracturing fluid imbibition in the formation. 1. INTRODUCTION Horizontal wells with multistage hydraulic fracturing are an important technical means for developing unconventional gas reservoirs (Fazelipour, 2011; Yu and Sepehrnoori, 2013; Lei et al., 2022). A large volume of water-based fracturing fluid such as slick water is injected into the formation to form a complex fracture network (Barati and Liang, 2014; Cai et al., 2017). Field practice shows that the flowback rate of fracturing fluid is generally low (Alkouh and Wattenbarger, 2013; Osselin et al., 2018). Spontaneous water imbibition is considered to be one of the main reasons for this phenomenon (Almulhim et al., 2014; Ge et al., 2015; Al-Ameri et al., 2018). The fracturing fluid spontaneously imbibes into the matrix from fractures, which could increase water saturation and reduce the gas phase relative permeability, affecting the production of gas reservoirs (Saini et al., 2021). The study of spontaneous imbibition mostly focuses on the capillary pressure of matrix pores and related problems (Makhanov et al., 2012; Dehghanpour et al., 2013; Roychaudhuri et al., 2013; Sadjadi and Rieger, 2013; Mason and Morrow, 2013; Shi et al., 2018). But spontaneous imbibition in unsaturated water fractures also deserves attention. There are different scales of fractures in the complex fracture network formed by artificial and natural fractures (Yushi et al., 2016). Studying the effect of fracture aperture on fracturing fluid imbibition into gas-saturated rocks has significance for improving fracturing technology and enhancing recovery.