Volume 63

Micro-CT Study of Pore-Scale Fluid Distribution in Low-Permeability Carbonate Gas Reservoirs Qingyuan Zhu, Keliu Wu, Tianduoyi Wang, Yaowei Huang, Tongchao Luan

Abstract

This study investigates water–gas displacement in carbonate reservoirs via in situ X-ray micro-CT. Miniature cores were scanned at staged conditions: connate water, 0.5 PV, 1 PV, and 50 PV. The images were processed to track the pore-scale evolution of gas–water distributions. Results show that during initial charging, gas preferentially occupies large pores with lower entry pressures, bypassing bound water in small throats. In the early flooding stage (0–0.5 PV), the wetting phase forms and thickens water films along pore walls, only compressing gas slightly and yielding limited mobilization. With continued injection (0.5–1 PV), gas is progressively removed from small to medium throats, while macropore gas remains largely unchanged. After substantial injection (1–50 PV), the water phase percolates and invades macropores, causing a marked drop in gas saturation and higher pore-scale displacement efficiency; however, intensified water blocking restricts gas flow, leading to diminishing incremental gains. During post-flooding stage, residual gas persists in blob-, cluster-, and dot-like morphologies across scales. The in-situ CT evidence clarifies interfacial evolution and trapping mechanisms relevant to mid-to-late development of edge-/bottom-water carbonate gas reservoirs. Corresponding mobilization strategies, such as optimizing drawdown, increasing displacement pressure, and reservoir depressurization, provide a theoretical and technological basis for improving gas recovery.

Keywords carbonate gas reservoir, micro-CT, connate water, residual gas, digital rock analysis