Study and application of ultra low density cementing technology for coalbed methane

Abstract：There are many problems in coalbed methane cementing resulted from the characteristics of coalbed formation,such as low pressure,low permeability and weak cementation.Aimed to solve these problems,evaluation experiments of light weight additive,baseline formula of cement system,low temperature early strength stabilizer,fluid loss additive and dispersing agent were performed.On this basis,the ultra low density cement slurry was developed.Besides,bridging type preflush was researched.The ultra low density cement slurry and bridging type preflush formed the ultra low density cementing technology for coalbed methane.There is no capillary channel in the surface of preferred hollow glass microsphere,so it has good resistance to pressure and shear.The ultra low density cement slurry has many good performances,such as no free liquid,slurry stability,small API filtration loss(≤45 mL/30 min),adjustable thickening time and early strength at low temperature.Moreover,the bridging type preflush has good filtration control property(≤19 mL/30 min),effective shut off capacity to the fractures and pores in the No.3 coalbed core,and good compatibility with ultra low density cement slurry.This ultra low density cementing technology has been applied in two wells for field trial successfully at Qinnan demonstration plot,and the service density is respectively 1.15 g/cm3 and 1.20 g/cm3.Acceptability of cement job quality is 100%,and high quality is above 96%.