关键词: 微观实验, 数值模拟, 微观滞留机理, CO₂提高采收率, 致密低渗气藏, 大牛地气田

Abstract:

The microscopic gas and water retention mechanisms in tight， low-permeability reservoirs are yet to be clarified， severely limiting the enhancement of oil and gas recovery of these reservoirs. The study delves into the microscopic mechanisms of gas and water retention in tight sandstone reservoirs and evaluates the feasibility of CO₂ injection for enhancing recovery rates via innovative microscopic experimental methods and numerical simulations. Specifically， we establish an entirely new microscopic retention experimental process， while overcoming the limitations of traditional experimental methods， such as ultra-low experimental pressures （less than 0.20 MPa）， and the mismatch between experimental processes and actual production conditions. Combined with the microscopic numerical simulation technique， we identify four primary gas and water retention types in tight sandstone reservoirs， i.e.， blind end-corner retention， bypassing retention， cut-off retention， and “H-shaped” pore retention. On this basis， the mechanisms behind CO₂ injection for enhancing gas recovery of tight， low-permeability reservoirs can be concluded. That is， the CO₂ injection serves to strip water film， facilitate the mass transfer and diffusion replacement of methane， as well as effectively displace gas， significantly increasing natural gas recovery from tight pore throats. The results reveal that CO₂ injection can enhance natural gas recovery rate by 10 % to 19 %， representing an innovative technological approach for the efficient exploitation of tight， low-permeability gas reservoirs.

Key words: microscopic experiment, numerical simulation, microscopic retention mechanism, CO₂ injection for enhancing recovery rate, tight and low-permeability gas reservoir, Daniudi gas field