The mud film thickness on the outer surface of casing and its distribution laws are important factors affecting the cementation quality at casing-cement interfaces.So far,however,the distribution laws of mud film thic...The mud film thickness on the outer surface of casing and its distribution laws are important factors affecting the cementation quality at casing-cement interfaces.So far,however,the distribution laws of mud film thickness on the outer surface of casing at different inclinations and its effect on the interfacial cementing strength have never been reported in literatures.In this paper,the mud film thickness at different parts on the outer surface of simulated casing(steel pipe)was measured at the inclination of 0°,30°,60°and 86°,respectively,using the independently designed experimental device.Then,the distribution law of mud film thickness on the outer surface of casing and its effect on the interfacial cementing strength were summarized.And the following research results were obtained.First,when the inclination increases from 0°to 86°,the mud film thickness changes from uniform distribution to thin-and-thick distribution,and the area proportions of thinner and thicker mud films both increase.And especially at the inclination of 86°,the mud film thickness on the upper surface is very large,and there are large exposed areas on the left and right surfaces of the steel pipe.Second,the cementing strength at the casing-cement interface of the exposed casing is much higher than that at the interface with mud film.And with the increase of inclination,the interfacial cementing strength with mud film tends to increase.Third,with the increase of inclination,the interfacial cementing strength increases successively,which is closely related to the area proportion of the exposed steel pipe to the solid mud film on the outer surface.In conclusion,the exposed area of the simulated casing on the outer surface is a key factor affecting its interfacial cementing strength.展开更多
The failure of cement sheath integrity can be easily caused by alternating pressure during large-scale multistage hydraulic fracturing in shale-gas well.An elastic-plastic mechanical model of casing-cement sheath-form...The failure of cement sheath integrity can be easily caused by alternating pressure during large-scale multistage hydraulic fracturing in shale-gas well.An elastic-plastic mechanical model of casing-cement sheath-formation(CSF)system under alternating pressure is established based on the Mohr-Coulomb criterion and thick-walled cylinder theory,and it has been solved by MATLAB programming combining global optimization algorithm with Global Search.The failure mechanism of cement sheath integrity is investigated,by which it can be seen that the formation of interface debonding is mainly related to the plastic strain accumulation,and there is a risk of interface debonding under alternating pressure,once the cement sheath enters plasticity whether in shallow or deep well sections.The matching relationship between the mechanical parameters(elastic modulus and Poisson's ratio)of cement sheath and its integrity failure under alternating pressure in whole well sections is studied,by which it has been found there is a“critical range”in the Poisson's ratio of cement sheath.When the Poisson's ratio is below the“critical range”,there is a positive correlation between the yield internal pressure of cement sheath(SYP)and its elastic modulus.However,when the Poisson's ratio is above the“critical range”,there is a negative correlation.The elastic modulus of cement sheath is closely related to its Poisson's ratio,and restricts each other.Scientific and reasonable matching between mechanical parameters of cement sheath and CSF system under different working conditions can not only reduce the cost,but also protect the cement sheath integrity.展开更多
基金Project supported by the Sub-project of National Major Science and Technology Project(No.:2017ZX05009003-003)the National Natural Science Foundation of China(No.:51774258,41572142).
文摘The mud film thickness on the outer surface of casing and its distribution laws are important factors affecting the cementation quality at casing-cement interfaces.So far,however,the distribution laws of mud film thickness on the outer surface of casing at different inclinations and its effect on the interfacial cementing strength have never been reported in literatures.In this paper,the mud film thickness at different parts on the outer surface of simulated casing(steel pipe)was measured at the inclination of 0°,30°,60°and 86°,respectively,using the independently designed experimental device.Then,the distribution law of mud film thickness on the outer surface of casing and its effect on the interfacial cementing strength were summarized.And the following research results were obtained.First,when the inclination increases from 0°to 86°,the mud film thickness changes from uniform distribution to thin-and-thick distribution,and the area proportions of thinner and thicker mud films both increase.And especially at the inclination of 86°,the mud film thickness on the upper surface is very large,and there are large exposed areas on the left and right surfaces of the steel pipe.Second,the cementing strength at the casing-cement interface of the exposed casing is much higher than that at the interface with mud film.And with the increase of inclination,the interfacial cementing strength with mud film tends to increase.Third,with the increase of inclination,the interfacial cementing strength increases successively,which is closely related to the area proportion of the exposed steel pipe to the solid mud film on the outer surface.In conclusion,the exposed area of the simulated casing on the outer surface is a key factor affecting its interfacial cementing strength.
基金Research work was financed by the National Natural Science Foundation of China(No.52074232)Sichuan Science and Technology Program(No.2022NSFSC0028,No.2022NSFSC0994).Without their support,this work would not have been possible.
文摘The failure of cement sheath integrity can be easily caused by alternating pressure during large-scale multistage hydraulic fracturing in shale-gas well.An elastic-plastic mechanical model of casing-cement sheath-formation(CSF)system under alternating pressure is established based on the Mohr-Coulomb criterion and thick-walled cylinder theory,and it has been solved by MATLAB programming combining global optimization algorithm with Global Search.The failure mechanism of cement sheath integrity is investigated,by which it can be seen that the formation of interface debonding is mainly related to the plastic strain accumulation,and there is a risk of interface debonding under alternating pressure,once the cement sheath enters plasticity whether in shallow or deep well sections.The matching relationship between the mechanical parameters(elastic modulus and Poisson's ratio)of cement sheath and its integrity failure under alternating pressure in whole well sections is studied,by which it has been found there is a“critical range”in the Poisson's ratio of cement sheath.When the Poisson's ratio is below the“critical range”,there is a positive correlation between the yield internal pressure of cement sheath(SYP)and its elastic modulus.However,when the Poisson's ratio is above the“critical range”,there is a negative correlation.The elastic modulus of cement sheath is closely related to its Poisson's ratio,and restricts each other.Scientific and reasonable matching between mechanical parameters of cement sheath and CSF system under different working conditions can not only reduce the cost,but also protect the cement sheath integrity.
