摘要：Hydraulic fracturing promotes the shale gas revolution worldwide. Since most of the fracturing fluids used now are water-based, shale hydration could happen before and after the treatment. However, the effects of shale hydration on hydraulic fracture initiation, fracture complexity, and proppant distribution have not been clarified. Thus, we performed shale hydration experiments on thin discs and cubic specimens under confining conditions to investigate the microstructure evolution through the scanning electron microscope (SEM) and acoustic emission (AE) system. Later, the hydrated cubic specimens were fractured to examine the impact of shale hydration on hydraulic fracturing through CT scanning. The results show that under confining conditions, water imbibition volume increases with time, but the effect of the fluid pressure inside the perforation on shale hydration is limited. The SEM images show that the preexisting microfractures extend at the beginning but stop growing with width reduction in 6 h, which is indirectly evidenced by the AE. The confining pressure inhibits the preexisting microfractures from opening and further propagation, resulting in closure of the microfractures near the perforation and the water imbibition stagnating. Those findings obtained from hydration experiments are verified by the hydraulic fracturing experiments, which show that the breakdown pressure increases with shale hydration. Meanwhile, the CT scanning shows that the fractures initiated from the vertical perforation become more complex after hydration, which leads to the width reduction of individual fractures and, consequently, poor proppant distribution. Therefore, it is suggested to utilize the optimal hydration time when microfractures expand or use clay inhibitors to decrease the breakdown pressure and facilitate the proppant placement. Imbibition time plays a key role in shale hydration, but the effect of fluid pressure is limited.Microfractures extend in the early stage of shale hydration and finally close due to confining pressure.Breakdown pressure increases in the hydrated shale after 6-h hydration under confining conditions (25-18-3 MPa).Due to stress condition differences, more complex near-wellbore fractures form in vertical perforations than in horizontal ones after hydration.Complexity of the near-wellbore fracture patterns cause poor proppant distribution for the hydrated specimens with a vertical perforation.

关键字：Shale hydration; Hydraulic fracturing; CT; Acoustic emission; Breakdown pressure; Proppant distribution

ISSN号：0723-2632

卷、期、页：卷57期3：1799-1814

发表日期：2024-03-01

影响因子：0.000000

期刊分区（SCI为中科院分区）：二区

收录情况：SCI（科学引文索引印刷版）,地学领域高质量科技期刊分级目录（国外T1）,EI（工程索引）,SCIE（科学引文索引网络版）

发表期刊名称：ROCK MECHANICS AND ROCK ENGINEERING

参与作者：李宁

通讯作者：高步栋,段贵府

第一作者：牟建业,邹雨时,张士诚,马新仿,王小琼

论文类型：期刊论文

论文概要：高步栋,牟建业,邹雨时,张士诚,马新仿,王小琼,段贵府,李宁，An Experimental Investigation into Effects of Shale Hydration on Breakdown Pressure and the Fracture Characteristics During Hydraulic Fracture Initiation，ROCK MECHANICS AND ROCK ENGINEERING，2024，卷57期3：1799-1814

论文题目：An Experimental Investigation into Effects of Shale Hydration on Breakdown Pressure and the Fracture Characteristics During Hydraulic Fracture Initiation