彭水地区龙马溪组页岩渗吸规律及渗吸动态分布

渗吸作为压裂液在储层中的主要吸收方式, 是提高页岩气产能的重要驱动力。以重庆市彭水地区龙马溪组页岩为研究对象, 依次进行毛管力测试、不同条件下的渗吸实验及核磁共振实验。结果表明: ①页岩的渗透率与孔隙度极低, 以微孔和小孔为主, 基本无大孔, 孔隙结构较差; ②页岩渗吸过程分为三个阶段, 随着压力和温度的升高, 渗吸效果增强, 破胶压裂液的渗吸效果略强于未破胶压裂液, 表面活性剂和KCl溶液可以降低页岩渗吸能力; ③页岩渗吸的核磁共振T₂谱具有明显的双峰特征, 渗吸过程中, 中大的孔隙和裂缝在初期阶段就被液体瞬间充满, 极微的孔隙和裂缝首先被充填, 随后液体进入稍大的微孔隙和微裂缝, 在渗吸过程中页岩表面产生大量的微裂缝。

Imbibition Behavior and Fluid Dynamic Distribution of Longmaxi Formation Shale in Pengshui Area

As the main absorption mode of fracturing fluid in reservoir, imbibition is an important driving force to improve shale gas productivity. In this paper, the Longmaxi formation shale in Pengshui area of Chongqing is studied. Mercury intrusion porosimetry, imbibition under different conditions and NMR tests were carried out successively. It shows that: ① The permeability and porosity of shale are very low, mainly micropores and mesopcres, almost no macropores, and the pore structure is poor; ② The process of shale imbibition can be divided into three stages. With the increase of pressure and temperature, imbibition behavior is enhanced. The imbibition effect of gel breaking fracturing fluid is slightly stronger than that of non-gel breaking fracturing fluid. Surfactant and KCl solution can reduce the imbibition ability of shale; ③ In the process of imbibition, the medium and large pores and fractures are filled with liquid in the initial stage, while the very small pores and fractures are filled first, and then the liquid enters into the slightly larger micropores and microcracks, resulting in a large number of microcracks on the surface of shale.