The High Temperature Effects on Pore Size Distribution of Tight Sandstone: An Application of Microwave Heating in Enhanced Gas Recovery (EGR)

Abstract

The present work studied the effects of microwave heating on sandstones with low porosity and permeability based on the comparison of pore size distribution (PSD) using Nuclear Magnetic Resonance (NMR) technique. Microwave heating can heat the sandstone in a short time and cause physical and chemical change of rock and fluids inside. The heat evaporated water and changed the structure of minerals and pores so that the permeability increased which was measured from the Automated Permeameter. Before microwave heating, all samples are prepared into three different water saturations for NMR measurements: fully saturated using high pressured saturator, partially saturated using centrifuge and dry using conventional lab oven. Then the T2 distributions were measured in three different conditions. Samples were prepared and measured in the same way after heating. It is found that Scanning Electron Magnetic (SEM), which can be used to compare the structure changes with high-resolution images, was used to support the NMR measurement; while Medical CT played a similar role by imaging full sample with lower resolution. Together they can give an interpretation of the T2 distribution or the pore size distribution. The permeability increased after heating and the T2 distribution of each sample has changed. Minerals have been changed due to water evaporation and high temperature. It accounts for the change of T2 distribution. Comparing plots and images before and after heating, the heating effects are obviously positive to EGR. We have had a good understanding of the effects of high temperature on permeability by studying the change of pore size distribution with NMR before and after heating. With the support of SEM and Medical CT, we got visualized evidence for our interpretation of the change of pore size distribution.