Liu Liangliang, Li Jing, Zhou Shixin, Chen Gengrong, Li Yaoyu, Pang Wenjun, Wang Hao
Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China.
Key Laboratory of Petroleum Resources Exploration and Evaluation, Gansu Province, Lanzhou 730000, China.
ACS Omega. 2024 May 8;9(20):22016-22030. doi: 10.1021/acsomega.3c10441. eCollection 2024 May 21.
Permeability is a significant characteristic of porous media and a crucial parameter for shale gas development. This study focuses on deep marine and marine-continental transitional shale in the southeastern Sichuan area using the gas pulse decay testing method to systematically analyze the gas permeability, stress sensitivity, and gas transport mechanisms of shale under different pressure conditions and directions. The results show that the porosity and gas permeability of the deep marine shale are greater compared to those of the marine-continental transitional shale. The elevated fluid pressure in the deep marine shale offers superior conditions for the preservation of nanopores, while the high quartz content provides advantageous conditions for fluid transport in nanopore channels. The permeability and stress sensitivity of the deep marine shale are greater than those of the marine-continental transitional shale, and the stress sensitivity is greater in the perpendicular bedding direction than in the parallel bedding direction, possibly related to the mineral composition of shale and the compaction it has undergone. The flow mechanism of the deep marine shale is transition flow and Knudsen flow, while that of the marine-continental transitional shale is transition flow. The deep marine shale possesses smaller nanopore sizes and a higher quantity of micropores, which create advantageous conditions for gas transport within nanopores. During the process of extracting shale gas, the extraction of gas causes a decrease in pore pressure and an increase in effective stress, resulting in a reduction in permeability. However, when the pore pressure reaches a specific value, the enhanced slippage effect leads to an increase in permeability, which is advantageous for gas extraction. In the later stage of shale gas well production, intermittent production plans can be developed considering the strength of the slippage effect, leading to a significant improvement in production efficiency.
渗透率是多孔介质的一个重要特性，也是页岩气开发的关键参数。本研究聚焦于四川东南部地区的深海相和海陆过渡相页岩，采用气体脉冲衰减测试方法，系统分析了不同压力条件和方向下页岩的气体渗透率、应力敏感性及气体运移机制。结果表明，深海相页岩的孔隙度和气体渗透率比海陆过渡相页岩更大。深海相页岩中升高的流体压力为纳米孔隙的保存提供了优越条件，而高石英含量为纳米孔隙通道中的流体运移提供了有利条件。深海相页岩的渗透率和应力敏感性大于海陆过渡相页岩，且垂直于层面方向的应力敏感性大于平行于层面方向，这可能与页岩的矿物组成及其所经历的压实作用有关。深海相页岩的流动机制为过渡流和克努森流，而海陆过渡相页岩的流动机制为过渡流。深海相页岩具有更小的纳米孔隙尺寸和更高数量的微孔，这为纳米孔隙内的气体运移创造了有利条件。在页岩气开采过程中，气体的采出导致孔隙压力降低和有效应力增加，从而使渗透率降低。然而，当孔隙压力达到特定值时，增强的滑脱效应会导致渗透率增加，这有利于气体开采。在页岩气井生产后期，可考虑滑脱效应的强度制定间歇生产计划，从而显著提高生产效率。
