Experimental and Numerical Studies on the Micro-fractures and its Significance Toward Production of Shales: A Case Study

Abstract

Abstract The mechanisms of shale gas storage and flow are complex. Understanding the microstructure is an important step for evaluating a new shale gas play toward accurate reserve estimation and recovery prediction. The emphasis of this paper is study on the micro-fractures observed on the research shale formation. The approaches involved in this study include experimental study and numerical modeling. Longmaxi Shale, which is an emerging Lower Silurian marine shale gas play in China with huge potential according to preliminary explorations, is the research formation in this paper. Core samples used in the experiment are collected from the target layer of Longmaxi Shale. The pore structure is visualized in nano-scale using Scanning Electron Microscope (SEM). In order to evaluate the influence of micro-fracture, a micro-model is built to explicitly simulate the micro-factures. The effect of micro-fracture on gas drainage capacity of shale matrix is then scaled up to a well model using a triple porosity approach. SEM images reveal well-developed micro-fractures on the Longmaxi Shale. Micro-fractures exhibit strong heterogeneity. The width, length and connectivity of the micro-fractures vary notably. This feature is believed can significantly influent the gas drainage capacity of shale matrix and as a result well performance. Sensitivity analysis is conducted by varying micro-fracture density, width, length and connectivity. Results show that micro-fracture plays an important role in production performance. This is because that the well-developed micro-fractures enhance the gas drainage capacity of shale matrix. Thus, micro-fractures observed in Longmaxi Shale have to be considered in evaluating potentials of this new shale gas play. This study characterizes the microstructure of Longmaxi Shale and discusses the significance of micro-fractures, which provides important information to support engineers and geologist for better understanding the marine shale and optimizing production plan on the marine shale.