CO2-Controlled Water Injection in Carbonate Gas Reservoirs: An Effective Approach to Improve Production.

In the development of edgewater-type carbonate gas reservoirs, the challenge posed by water flooding in production wells is a significant concern. This study investigates the potential of CO2 injection as a solution for water control. Experiments were conducted to understand the gas-water flow dynamics during CO2-controlled water injection in a series-connected core. Emphasis was placed on the effects of varying the CO2 injection pressure on water flow and gas cumulative production rate. The mechanisms influencing water control and production efficiency across different injection pressures in multiwell production were elucidated. The results showed that the gas production rate of the core increased by 27.2% over the depletion production rate after the CO2 injection pressure was increased from 8 to 13 MPa. The gas production rate increases during the second development cycle from 20% to 55% after switching to CO2 injection, which pushes the edge water further back, slowing down side water flow in the core in the form of segmental plugs, and prolonging the time before water breakthrough. The production time and water breakthrough time for the second development cycle increased with increasing CO2 injection, while the degree of water flow on the core side decreased. These insights are crucial for optimizing the recovery efficiency of edgewater-type gas reservoirs and provide guidance on the application of CO2 injection for water control and CO2 sequestration in carbonate gas reservoirs.

Research on the control of overburden deformation by filling ratio of cementing filling method with continuous mining and continuous backfilling.

Underground resource exploitation has seriously damaged the surface ecological environment and underground water system. As an effective control measure, the filling mining process has greatly reduced the surface subsidence. As a branch of the filling mining process, the continuous mining and continuous backfilling (CMCB) method solves the contradiction of mining and filling in this process. The control index of filling ratio of even number lane (FRE) was presented to investigate the technical advantages of the CMCB method. The numerical analysis model was used to investigate the laws such as deformation characteristics of the surrounding rock, stress distribution, and plastic area distribution characteristics of backfill under four typical cases. As a consequence, the FRE effect law on overburden deformation and the roof control function of the backfill was disclosed, and overburden rock deformation control solutions were provided. According to the results, the overburden deformation varies dramatically when the FRE decreases, and it rises greatly when the even-numbered lane backfill (ELB) is not contacted with the roof. The contacting condition and filling condition of the odd numbered lane backfill (OLB) are connected to the distribution of stress and plastic zone. The backfill transmits the rock beam load by building a composite support system with the roof and floor rock layers, and it accomplishes the backfill's roof control function by combining the primary and secondary load-bearing and synergistic load-bearing connections between the backfills. Measures such as differential FRE, differential strength, non-uniformity of filling lane, and synergistic bearing of temporary support and backfill may help to decrease deformations and internal cracks in the surrounding rock. This measure has been successfully implemented in the field, serving as an experience for the application of the CMCB method.