CO-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 CO injection as a solution for water control. Experiments were conducted to understand the gas-water flow dynamics during CO-controlled water injection in a series-connected core. Emphasis was placed on the effects of varying the CO 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 CO 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 CO 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 CO 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 CO injection for water control and CO sequestration in carbonate gas reservoirs.