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

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 oilbearing sandstone formation. Experimentally, thin sections were prepared out of core samples collected from a tight formation, and corresponding analyses were performed by using the scanning electron microscopy and x-ray diffraction 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 and rate-controlled mercury injection, respectively, to quantify the changes in microscopic pore-throat structure after brine-flow tests. Subsequently, displacement experiments of water flooding 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 were found to possess complex compositions, and both intergranular pores and intragranular dissolution pores were dominant. Nanothroats may have developed in a tight formation because of small radii of pores and throats. Compared with the pore size distribution, throat radius was found to be reduced by 13.9% after brine-flow tests, and the cutoff value of movable throat can be decreased to 0.019 from 0.033 mm by using a surfactant.