Study On The Optimization Of Cementing Scheme For PVC Casing Pipe In Coalbed Methane Horizontal Well

The U-type horizontal well is mostly used for coalbed methane mining.As a brand new kind of completion casing pipe,PVC casing pipe is widely used in horizontal section completion of coalbed methane well.Compared with steel casing,PVC casing pipe can ensure its strength to meet the construction requirements,and will not generate electricity and friction sparks in the coal mining process.Thus it can avoid gas explosion and improves the safety of mining process.Because of PVC casing pipe's low density,during different stages of horizontal well cementing process,due to the density difference of the internal and external pipe,casing eccentricity will be caused,which affects the process of cementing displacement efficiency and ultimately harms cementing quality.Considering the density difference,this paper established casing central degree calculating model for evaluating casing central condition in different cementing stages.As calculating results showed,casing central degree cannot meet cementing demand.Therefore,this paper proposed the method for improving casing central degree is using centralizer.On the basis of mechanical analysis,this paper presented another casing central degree calculating model under the effect of centralizer.By clarifying the influence of centralizer's distance and location on casing central degree,the placing method of centralizer was optimized.For guaranteeing the displacement quality of cementing in horizontal section,this paper analyzed the effect of casing central degree on displacement efficiency and presented the influence rule by combining with numerical simulation results in different displacement flow state.In view of the large pressure of dynamic fluid column may generate leakage of fluid in annulus,and even fracture coal bed during turbulence displacement.In process of slug flow displacement,too much time will be cost which may cause a loss of cement slurry flow property.By considering above,this paper established “Flowage friction–displacement volume reverse calculation method” for accomplishing optimization of cementing displacement volume in the state of laminar flow,and provided the theoretical basis for scheme design of cementing in coalbed horizontal well.