Influence of mud filtrate on the pore system of different sandstone rocks

During drilling the oil and gas wells, the drilling fluid is used for many purposes in the drilling operations. The mud filtrate might invade the formation, and as a result, alterations will occur to the internal pore structure. Therefore, this research aims to investigate the mud filtrate impact on the pore system of different sandstone rocks which are Berea (Buff and Spider), Bandera Brown, and Parker. Water-based mud (weighted with barite) was employed to prepare the mud filtrate. Then, rock-filtrate interaction was executed under simulated downhole conditions of pressure, temperature, and time (300 psi, 200 °F, 10 days). A deep investigation laboratory experiment was designed as X-ray diffractions for mineralogical composition for the rock sample, scanning electron microscopes for capturing the pores internal topography, and nuclear magnetic spectrometry to detect the pore structure changes. The obtained results represented severe changes in the rock internal topography that are attributed to the different reactions of mineral compositions with the mud filtrate. Berea types (Buff and Spider) showed major changes in the pore size distribution compared to Bandera Brown and Parker rock types. There were insignificant changes in the total porosity after the rock-filtrate interaction, however, an overall decrease was found for the rock pore throat radius and the permeability values with different degrees; and these alterations affected the flow characteristics as the porous system of Berea Buff and Parker converted from macro-porous to meso-porous system.