A New Method of Simulating Micro Fractures in Shale and Plugging Evaluation Experiment

There are many methods available presently for the simulation of micro fractures in Shale. All these methods have limitations, and are unable to trulysimulate the hydration and dispersion processes of shales in contact with water at HTHP conditions. To solve this problem, several simulation methods, such as the smooth steel block simulation method, sand bed plugging experiment method, simulation with artificial fracture (on split rocks) method and transparent tampered glass simulation method etc. were analyzed, and based on the analysis, a new method has been developed. In thenew method, a standard core plug is obtained by dry drilling samples,and artificial fractures are then made in it.The surface of the artificial fractures is covered with tinfoil of different thickness to simulate micro fractures of 10-100 μm in width. The core plug is put into a core holder that is connected with dynamic filter press, and a device for evaluating the capacity of plugging micro fractures in shale is formed. The assembly of the device, the experimental procedure, the function and the advantages of the device are introduced in this paper. An equation for the calculation of the width of micro facture is presented, and the equivalent widths of micro fractures are calculated through conversion of accurately measured data. Laboratory experiment has shown that this simulation method has high precision and good repeatability. This method can be used not only to simulate the hydration, dispersion and swelling of shale in contact with liquids, but also to simulate the plugging of micro fractures by drilling fluid on bottom hole at high temperature and high pressure. The simulation can be used to extensively study the plugging mechanism of micro fractures to provide reliable experiment method and datasupport for the selection of plugging agent and optimization of drilling fluid formulation.