Effect of Supercritical Carbon Dioxide Treatment Time, Pressure, and Temperature on Shale Water Wettability

Abstract

Supercritical carbon dioxide (SC-CO 2 ) fluid can dissolve surface matter on shale and, thus, change the surface properties of shale. To study the influence of SC-CO 2 on the water wettability of shale, shale samples collected from the Longmaxi formation in Sichuan Basin were treated with SC-CO 2 at various time intervals, pressures, and temperatures. The results show that, after SC-CO 2 treatment, the ratio of C and Si in the shale increased, while the ratio of O, Ca, Mg, and H decreased. Water was released from the clay minerals, and the CaCO 3 content decreased in the shale. After SC-CO 2 treatment, the primary pores and fractures in the shale were eroded through dissolution and new pores and fracture structures were developed on the surface microstructure of the shale. As a result, the structure connectivity, which favored the seepage of shale gas, was improved. The results also show that the shale−water contact angles were increased after SC-CO 2 treatment. The treatment time and pressure had a significant influence on the contact angles, but the effect of the treatment temperature on contact angles was not obvious. The change in the contact angles resulted from a reduction of the CaCO 3 content on the shale surface, which decreased the surface hydrophilicity. The shale surface water wettability and the shale surface tension were decreased after SC-CO 2 treatment. This reduces the hindrance function of water in the shale minimal pores and fracture, which is beneficial to CO 2 diffusion into the shale matrix. This promotes CO 2 adsorption capacity in the shale as well as CH 4 desorption from the shale. This study provides a theoretical basis for using SC-CO 2 fluid for efficient shale gas exploitation in the Longmaxi formation of the Sichuan Basin.

Molecular insights into competitive adsorption of CO2/CH4 mixture in shale nanopores

“…10 Due to the characteristics of supercritical carbon dioxide (Sc-CO 2 ), including its low viscosity, high diffusion capacity near gas and high density near liquid, it has unique advantages for the shale gas extraction. 11 Additionally, much research has shown that preferential adsorption of carbon dioxide over methane, which indicates the feasibility of CO 2 sequestration with enhanced gas recovery (CS-EGR) in shale reservoirs. 12,13 Although the CS-EGR technique in shale has not yet been widely commercialized, extensive investigations have been carried out in this eld.…”

A Review on the Influence of CO2/Shale Interaction on Shale Properties: Implications of CCS in Shales

“…In the last decade, enormous work was directed towards understanding the fundamentals of the CO 2 -shale interaction at reservoir conditions for better CCS applications [42][43][44][45][46][47][48][49][50][51][52], by evaluating the impact of CO 2 injection on shales. Earlier in 2008, Busch et al [53] found that the rock properties of Muderong shale in Australia were affected by the dissolution behavior of SCCO 2 .…”

“…Hence, it is necessary to address the complex nature of shales' wettability and analyze the factors involved, i.e., pressure, temperature, pH, mineral composition and TOC [85]. Several studies were conducted to evaluate the wetting behavior of different types of shales at the presence of different fluids, by using different methods and techniques, such as equilibrium contact angle (sessile drop) [44,[86][87][88][89][90], NMR [91], spontaneous imbibition [92][93][94][95][96], and liquid-liquid extraction [87].…”

Effects of Supercritical CO2 Treatment Temperature on Functional Groups and Pore Structure of Coals

“…This is because temperature influences the supercritical fluid density. Under the same pressure, the density of ScCO 2 decreases as temperature increases, and the solubility of ScCO 2 decreases [50,51].…”