Irregular borehole cementing technology in leakage wells of Yanchang gas field

The formation in the Yanchang gas field is characterized by low pressure coefficient, thick gas bearing formation, rich groundwater, and destabilization shale, coalbed interaction complex formation, which result in “tomatoes on stick” borehole. There are some troubles occurred during the cementing operation, such as insufficient cement slurry return due to lost circulation, serious channeling among annular gas, water and drilling fluid, and only 16% cementing quality up to excellence. By optimizing cement slurry system, designing rational column structure, figuring out the weak formation through data of pore pressure, rocky density, drilling rate and pressure profile, selecting reasonable riding position of stage collar, and applying positive injecting and negative infusing completion technique, successful solve the problems of lost circulation in the process of well cementing and gas, water channeling during curing time. The results show that the cementing quality excellent rate is up to 93.54% by the treatment, which realize the target of whole well effectively cementing by cement slurry.