Characterisation of fines migration system using laboratory pressure measurements

Abstract

The focus of this study is formation damage due to fines migration induced by the leak-off of low salinity potassium chloride (KCl) fracturing fluids. The importance of this topic is determined by the wide utilization of KCl in drilling and fracturing fluids, as well as for fines fixing, and the widely reported skin in gas and oil wells. Scanning electron microscopy (SEM) imaging and energy dispersive X-ray (EDX) analyses from this study clearly indicated clay fines mobilisation, migration and straining, resulting in permeability decline. The breakthrough fines concentration was measured during the coreflooding experiments. The installation of a pressure sensor in the middle of the core allowed for pressure drop measurements across the first core section and the overall core. Permeability decline was observed during the injection of water with piecewise-constant decreasing KCl salinity. An analytical model based on the exact solution for one-dimensional fines transport was used to match the laboratory data. Close agreement between the laboratory and modelling data was observed. Moreover, the tuned model coefficients vary in the range of commonly reported values. It was found that neglecting fines breakthrough concentration (BTC) measurements permits laboratory-based prediction of formation damage during fracture fluid leak-off. However, fines BTC must be measured to fully characterise the fines migration system.