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

详细信息    查看全文

• 作者：Chao Qin ; Yongdong JiangYahuang Luo ; Xuefu Xian ; Hui Liu ; Ye Li
• 刊名：Energy & Fuels
• 出版年：2017
• 出版时间：January 19, 2017
• 年：2017
• 卷：31
• 期：1
• 页码：493-503
• 全文大小：766K
• ISSN：1520-5029

文摘

Supercritical carbon dioxide (SC-CO₂) fluid can dissolve surface matter on shale and, thus, change the surface properties of shale. To study the influence of SC-CO₂ on the water wettability of shale, shale samples collected from the Longmaxi formation in Sichuan Basin were treated with SC-CO₂ at various time intervals, pressures, and temperatures. The results show that, after SC-CO₂ 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 CaCO₃ content decreased in the shale. After SC-CO₂ 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-CO₂ 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 CaCO₃ content on the shale surface, which decreased the surface hydrophilicity. The shale surface water wettability and the shale surface tension were decreased after SC-CO₂ treatment. This reduces the hindrance function of water in the shale minimal pores and fracture, which is beneficial to CO₂ diffusion into the shale matrix. This promotes CO₂ adsorption capacity in the shale as well as CH₄ desorption from the shale. This study provides a theoretical basis for using SC-CO₂ fluid for efficient shale gas exploitation in the Longmaxi formation of the Sichuan Basin.