Abstract: Deep carbonate gas reservoirs with complex pore structure and large variation in productivity challenge the efficient development and long-term stable production, and there is an urgent need to conduct targeted study on the law of natural depletion under stratigraphic conditions. To this end, the pore structure of gas reservoirs was characterized in detail with secondary CT scanning technology, and the influence of pore structure and irreducible water on natural depletion under stratigraphic conditions was investigated by core tests. The results showed that, the uneven development and distribution of pores and fractures was the root cause for the strong heterogeneity and large variation in productivity of this type of gas reservoir; the gas production was mainly controlled by the porosity, and the recovery efficiency was close to a logarithmic relationship with permeability; when the downhole pressure was 15 MPa, the average recovery efficiencies of porous, vuggy, fractured porous and fractured vuggy reservoirs were 47.43%, 48.21%, 59.90% and 62.14%, respectively; the reserve, gas production and recovery efficiency of the fractured porous reservoir were relatively high; the vuggy reservoir was featured by high reserve and low gas production rate, with an obvious characteristic of high porosity and low production; the fractured porous reservoir was characterized by low reserve, fast gas production rate and short stable production period; the porous reserve was relatively low both in reserve and gas production rate. The results of the study provide a theoretical basis for the development plan design of deep high pressure carbonate gas reservoirs.

Key words: deep carbonate gas reservoir, high temperature and high pressure, pore structure, irreducible water, natural depletion, stage recovery degree