Research On Damage Of Casings Used In Deep/ultra-deep Well Salt Layers Drilling

Tarim Basin has a large set of salt layer,thickening casing can solve the casing damage to certain extent in the pediment region.However this problem is still outstanding in North Tarim.The Carboniferous Salt layers are mainly composed of pure salt rocks,and mixed with mudstone and gypsum rock interlayers with different thickness.Drilling through the salt layer,the original stress field imbalances,which results in the rheological of formation.For different mechanical properties,stress concentration occurs at the interface of different lithological strata.At this point on the salt layer,according to the overlying strata pressure designing casing selection,the casing strength will be insufficient,leading to the casing deformation damage.The wells of casing damage are mainly deep/ultra-deep well.The strata where the damage happens are concentrated in the salt gypsum rock,which is the dangerous section of the casing damage.So this article based on the theory of elasto-plasticity,the interfacial mechanical model of horizontal geostress calculation at the creep of the salt bed is established.The stresses in the different deviation stresses and different mudstone content are calculated,verified by using ABAQUS.The influence of different mudstone interlayer content on the horizontal inhomogeneous principal stress was analyzed.The mechanical model of casing-salt assemblage was deduced,and the impact of formation shrinkage and the degree of inclination of mudstone interlayer on casing load were analyzed.Based on the model,the casing damage in Yuke area is analyzed and it is found that the casing load has exceeded its casing strength,and a new method of casing design is put forward.