Research and Practice of CO2 Energized Fracturing Technology in Changqing Gas Field

The Changqing tight gas reservoir is characterized by low pressure, tight and easy to be water locked. Large-scale fracturing of unconventional reservoirs requires a large amount of water, and it is difficult to deal with flowback fluid, so the safety and environmental protection situation is severe. By taking advantage of the unique physical and chemical properties of liquid CO2 such as low viscosity, good fluidity, strong diffusion, easy dissolution and mineral reaction, it plays a role in penetrating, breaking through rocks, increasing permeability and creating fractures, boosting energy storage, reducing damage, and solidifying and sealing for tight, low-pressure, easily water locked and water sensitive reservoirs. In this paper, the pre- CO2 energized and pressurized model of single well is established, forming pre- CO2 energized fracturing technology models for different reservoirs; Besides it research and develop new high-efficiency foaming agent, innovate to form CO2 foam fracturing fluid system, realize water reducing, sand increasing and high fracture conductivity during fracturing, and form CO2 foam water reducing fracturing technology. Changqing Oilfield has carried out 116 wells of CO2 fracturing technology experiment, with the average daily gas production increased by more than 10%. Four wells of CO2 foam fracturing experiment have been carried out in coalbed methane and northeastern Sulige, with the water reducing rate of 50%, creating the engineering index of 200 m3 single stage sand addition and 1100kg/ m3 maximum surface sand concentration, which has become a new way for efficient development of coalbed methane and low-pressure water locked reservoirs.