The breakthrough pressure and sealing property of Lower Paleozoic carbonate rocks in the Gucheng area of the Tarim Basin

Abstract

Deep carbonate reservoirs with great resource potential are key areas for future hydrocarbon exploration with the continuous innovation of deep hydrocarbon accumulation theory and technology. Breakthrough pressure (BP) is the most important parameter used to indicate rock sealing. In this study, X-ray diffraction, CO2 adsorption, N2 adsorption, high-pressure mercury injection, thin section analysis, effective porosity-permeability and BP experiments are conducted to research pore-throat characteristic of carbonate rock and the influencing factor of BP. Pore volume increases with the specific surface area (SSA) of micropore, and has a weak negative and positive correlation with the SSA of mesopore and macropore, respectively. The BP increases with an increase in the micropore proportion and decreases with an increase in the macropore proportion. Compared with R50 (the pore-throat radii corresponding to these mercury saturation of 50%), R35 (the pore-throat radii corresponding to these mercury saturation of 35%) has a better correlation with porosity and permeability and can better characterize the influence of pore throats on the sealing performance of carbonate rock. A low clay content perhaps leads to an inapparent interrelation between clay content and BP. Because of high brittleness of quartz, an increase in quartz content will cause an increase of porosity and permeability, and a decrease in BP. The BP decreases with the increase in effective porosity and permeability, and linear correlations exist among the reciprocal of porosity (A), the −0.407 power of permeability (B), and the BP. The BP calculation formula is fitted based on A and B by the principal component regression (PCR) method of SAS software for carbonate rock in the Ordovician of the Gucheng area.