Saturation model for pore-type gas hydrate based on additional muddy conductive digital core

Abstract

Abstract Original natural gas hydrate rock samples readily decompose under environmental changes during extraction, presenting challenges to conventional rock electrical analysis. This results in difficulty obtaining the cementation factor m and saturation exponent n of hydrate samples, thereby complicating the evaluation of hydrate saturation. Therefore, a method for revising the rock electrical parameters by digital core technology is proposed. Utilizing X-ray CT images of artificial gas hydrate samples, digital core models of natural gas hydrates were established. An erosion algorithm was employed to simulate the variation in mud content within the digital core, followed by the calculation of resistivity using the finite element method after meshing. Through analyzing the primary micro-pore structure parameters that influence the rock electrical parameters, the saturation model was subsequently refined. The results showed that the resistivity of hydrate digital core magnifies with increasing saturation of hydrate, tortuosity, and pore-throat ratio, but decreases with increasing coordination number and mud content. The rock electrical parameters were changed with the alteration of micro-pore structure. Based on the relationship between m, n, and micro-pore structure parameters, established a correction equation for them, further improved the Indonesian equation. The saturation of hydrate reservoir in Shenhu Sea area was evaluated using the modified Indonesian equation. The modified equation reduced the relative error from 34.8% to 15.6%, significantly enhanced the calculation accuracy.