Nanoscale deformation and crack processes of kaolinite under water impact using molecular dynamics simulations

Abstract The mechanisms of deformation or crack of nanoscale clay particles under water impact is important yet not investigated thoroughly. Hydraulic fracturing method is used for shale gas extraction, since large amount of water is injected into deep shale formations to crack rocks and release trapped gas. In this work, the microscopic deformation and crack processes of kaolinite (Kaol) pores under high-pressure water impact are investigated using molecular dynamics simulations. Two modes of water impact are adopted. These modes are distinguished by the directions of extra force which is exerted on water clusters to crack the Kaol rock. The results show that Kaol with two distinct basal surfaces exhibit different deformation features under these two impact ways. The falling apart of SiO tetrahedral or AlOH octahedral units leads to cracks or apertures. An integrated arrangement of small SiO tetrahedral units is observed while AlOH octahedral units are not. After cracking, water cluster enters the pore space and adsorbs onto the polyhedral units of Kaol, especially surrounded by close-packed SiO tetrahedral units. In addition, the changes of mechanical equivalent stress during the deformation and crack process are analyzed. This work provides a molecular explanation of the microscopic mechanisms and processes of rock cracking, and guidance for hydraulic fracturing fluid improvement.