Study On The Effect Of Cement Sheath Quality On The Collapsing Strength Of Casing During Stimulation

The permeability of shale reservoirs is extremely low,and natural fractures must be communicated through stimulation(large staged fracturing)for commercial exploitation.However,during the large staged fracturing,the induced stress induced by hydraulic fracture will change the size and direction of the In-situ stress around the wellbore.At the same time,the high injection pressure will cause the wellbore to bear great alternating stress.Both of them will cause casing deformation damage and damage wellbore integrity.The cement sheath has a certain effect on the protection casing and the unloading casing.However,the cement sheath quality has not been studied in depth on the casing collapsing strength.At the same time,the staged fracturing will put forward higher requirements on the quality of cement sheath.Therefore,this paper focuses on the experimental and theoretical study of the relationship between cement sheath quality and casing collapsing strength.In this paper,the collapsing strength of casing is used to express the equivalent collapsing strength of the casing.This paper shale reservoir in sichuan area as the research object,through the independent design of the hydraulic casing confining pressure simulation experiment combined with numerical simulation software of ABAQUS,simulation research on fracturing conditions cement sheath quality,the effects on the casing collapsing strength.The main achievements are as follows:1)The influence of cement sheath quality on the casing collapsing strength.(a)The cement sheath has a certain protective effect on the casing.Compared with the non-cement sheath,the casing collapsing strength is increased by about 7%.(b)The casing collapsing strength with the increase of elastic modulus of cement sheath,the thickness of cement sheath in the Angle of the center Angle is increased,the increase of the short axis length of the cement sheath gas invasion channel,the increase of the horizontal principal stress ratio,the casing is moderately reduced lower and lower.(c)when the cement sheath is completely absent from the Angle of the center Angle,a small confining pressure is applied and the cementation of the interface will be destroyed.The casing collapsing strength has not changed.2)The calculation of casing collapsing strength in the case of cement sheath protection.Considering the quality of cement sheath and the proportion of different size horizontal principal stress effect on the casing collapsing strength,according to the experimental results,it is concluded that the casing design and stimulation more reference casing collapsing strength calculation formula.