Abstract
Understanding spontaneous imbibition helps to determine the fracturing fluid volume and optimize the flowback design. At present, many studies have mainly focused on shale, but few on igneous rocks. As such, in this study, imbibition experiments were conducted on igneous rocks. The effects of KCl concentration, confining pressure, and imbibition direction on the spontaneous imbibition were systematically investigated. This study then introduces a new imbibition capacity index. The results show that KCl concentration has certain inhibitory effects on igneous rock imbibition, which reduce the absorption of clay minerals to liquid. Different imbibition directions result in distinct imbibition volumes. The co-current imbibition process is similar to fluid leak-off, but this rule is not satisfied in countercurrent imbibition, the n of which is fitted as 0.1.0.3. Increasing the confining pressure will slightly decrease the imbibition capacity of igneous rock. Rock imbibition causes a decrease in the surface hardness and physical properties of igneous rock, and increasing the KCl concentration in the fluid will effectively hinder clay swelling.
Highlights
Unconventional reservoirs have become the focus of research seeking to explore and develop oil and gas (Zou et al 2018)
The results show that spontaneous imbibition in deionized water is larger than that in KCl solution and much larger than that of kerosene
The confining pressure of the rock sample is controlled by the confining pressure pump and gripper, and the imbibition volume can be determined by a metering tube
Summary
Unconventional reservoirs have become the focus of research seeking to explore and develop oil and gas (Zou et al 2018). Dehghanpour et al (2013) studied the spontaneous imbibition capacity of deionized water, KCl solution, kerosene, and other liquids. The results show that spontaneous imbibition in deionized water is larger than that in KCl solution and much larger than that of kerosene. Deionized water still induces fractures and clay swells; there is no obvious change and slight contraction at 10% NaCl. Zolfaghari et al (2016) investigated the effects of clay content and specific surface area on the spontaneous imbibition process. Minardi et al (2018) quantified the impact of the swelling and shrinkage of gas shales during imbibition and desiccation processes They found that swelling of the shale rock leads to more than 40% imbibed water volume. A new imbibition capacity index Ct is introduced to characterize the experimental data
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