Influence Of Pore Structure On Gas Flow And Recovery In Ultradeep Carbonate Gas Reservoirs At Multiple Scales

Ultradeep carbonate gas reservoirs are a major resource of interest in clean energy development, and complex pore structures and reservoir conditions with high-temperatures and pressures are great challenges to efficient development and experimental research. It is becoming increasingly imperative to study the influence of pore structure on gas flow and productivity under reservoir conditions. Taking an ultradeep carbonate gas reservoir in the eastern Sichuan Basin, SW China, as the target reservoir, the pore structure was accurately analyzed and classified by X-ray computed tomography scanning. On this basis, three representative pore network models were established to simulate and visually analyze the gas flow characteristics at the pore scale, which effectively supplemented and perfected previous core experiments and 2D visualization research. A high-temperature and high-pressure experimental platform was built, and the influence of pore structure, heterogeneity, and irreducible water saturation (SWI) on gas flow and recovery was studied quantitatively and qualitatively for the first time through improved core experiments. The results showed that fracture characteristics, pore connectivity, and water saturation are key factors affecting gas flow and depletion strategies, and cavities constitute the main reservoir space. Under no-water conditions, the final recovery nears 72.24%, and the influence of pore structure is not obvious. Under SWI conditions, the gas flow resistance increases, and the loss of the production rate is higher than 27% based on the similarity transformation; the lower the permeability or production pressure difference is, the higher the production rate loss will be. At the same time, irreducible water leads to significant recovery losses; the final recovery is between 57.95 and 71.10%, and the recovery loss of the pore-type reservoir is much higher than that of the fracture-type reservoir. In gas reservoir development, increasing permeability is conducive to improving the production rate and recovery, especially for ?high-porosity and low-permeability? reservoirs. If the permeability is high enough, the production pressure difference should be controlled to avoid insufficient gas supply from far-well areas and reduce interlayer interference. Therefore, it is of great significance to promote coordinated development between multiple layers in the vertical direction and between near-well area and far-well areas in the horizontal direction.