Research On Mechanism And Countermeasures Of Casing Damage Of Carboniferous Salt Gypsum Rock Layer In Tarim Oilfield

The Oil and gas development in the Yuke block of Tarim Oilfield,the biggest difficulty encountered in engineer is casing damage in the Carboniferous salt layer,which brings great impact and loss to the oil and gas production?Therefore,the research of load and damage of casing in salt gypsum layer is of great importance for the rational design of the well structure,the determination of the steel grade and wall thickness of casing,and the prevention of casing damage in the later stage?The paper aims at solving the problem of casing damage in the yuke block,On the basis of a large number of literature research,combined with indoor rock mechanics experiments,theoretical analysis and numerical simulation,the conclusions are as follows:(1)For the Carboniferous salt gypsum strata with higher stress and lower temperature,the creep mechanism of the rock belongs to the dislocation glide mechanism,and the Heard creep model should be selected.(2)The parameters of rock mechanics,salt mineral composition and salt rock creep law are obtained by triaxial rock mechanics experiment,XRD mineral diffraction analysis experiment and creep experiment.The parameters of creep constitutive model are also obtained,which provides basic data for the next calculation.(3)the force of the casing body is analyzed by FLAC3D software,The results show that the maximum Mises equivalent stress of the casing is in the process of dynamic change,and the stress increased rapidly at the initial stage,and then gradually decreased the final equilibrium after reaching the peak.The casing is subjected to compression deformation in the direction of maximum stress and tensile deformation in the direction of minimum stress.(4)The degree of heterogeneity of the in-situ stress will change the peak of the maximum equivalent stress of the casing,but the final result is not much different.The spiral deformation of the cement ring will cause the stress concentration of the casing locally,resulting in a sharp increase in the equivalent stress.The spiral loss of cement will cause stress concentration in the casing,which leads to a dramatic increase in equivalent stress,especially in the absence of 90°to 270°.(5)Proposing a well structure improvement program,salt layer in the two-section will use the thick wall casing of high-grade steel(TP140V 26.24mm),and hang P110tail pipe inside the above casing to form a composite casing structure,and further enhance the whole casing Anti-squeeze ability,after checking the new well structure meet the tensile,compressive and Anti-squeeze requirements of casing in salt.The drilling fluid system uses saturated brine drilling fluid or oil base mud,and the upper limit of density is increased to 1.70g/cm~3.