Determination of static and dynamic characteristics of microscopic pore-throat structure in a tight oil-bearing sandstone formation

Abstract

In this study, an integrated and practical framework has been developed to quantify the static and dynamic characteristics of microscopic pore-throat structure in a tight oil-bearing sandstone formation. Experimentally, thin sections were prepared out of core samples collected from a tight formation, while corresponding analyses were respectively performed by using the scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. In addition to pore types and clay minerals, the size, fraction and distribution of grains were identified and classified. Pore and throat size distributions were then determined by using pressure-controlled mercury injection (PMI) and rate-controlled mercury injection (RMI) respectively to quantify the changes in microscopic pore-throat structure after brine flow tests. Subsequently, displacement experiments of waterflooding and surfactant flooding were performed to determine the upper and lower cutoff value of the movable throat radius. Rock grains primarily containing fine sand and silt are found to possess complex compositions, while both intergranular pores and intragranular dissolution pores are dominant. Nano-throats may have developed in a tight formation due to small radii of pores and throats. Compared to the pore size distribution, throat radius is found to be reduced by 13.9% after brine flow tests, while the cutoff value of movable throat can be decreased to 0.019 µm from 0.033 µm by using a surfactant.