Study On The Mechanical Mechanism Of Oilfield Injection-production-induced Shear Casing Damage

The geological environment of oil and gas reservoir is complex for the distribution of more faults and mudstone interbeds.In the course of many years of water injection cyclically,the effective stress of oil field is decreased by the influence of high pressure water,the activity of fault is increased and the ereep deformation of mudstone interbeds is increased gradually.The casing in oil field is failed by shear because of these cases,and the economic loss is larger.Therefore,the mechanism and prevention of casing damage and control measures have become an important problem to be solved in oilfield development.The causes of casing failuse are summarized and analyzed,the change of casing stress and shear failure caused by faults slip and mudstones creep is discussed.At the same time,some suggestions for reducing the rate of casing damage combined with the actual situation of oil field.(1)The failure criterion and failure reason of casing are analyzed and sumnarized,engineering criterion for casing shear failure is obtained.The geological factors and engineering factors that cause failure by shear are discussed.(2)The finite element model that contains fault zone is established,the influences of fault type,fault dip angle and thickness on the shear stress of the casing axe studied-The composite fault is more serious than the single fault;the larger the dip angle is,the larger the shear stress is;the thickness of fault zone is inversely proportional to the shear force.(3)B-K model is improved.Creep constitutive equation of mudstone influenced by water content is established.The parameters of actual oilfield well pattern are selected,the numeriacal model is established,and the water content of mudstone is adjusted by changing the injection production ratio,the variation of casing shear force under different parameters is simulated.(4)The typical S142 and S177 blocks are selected through the actual geological and the injection production parameters of Shengping oilfield.the influence of fault slip and mudstone creep on the variation of casing shear stress was simulated,and the corresponding prevention and control measures are proposed.The simulation results of two block are well fitted with the historical recovery rate,and the numerical simulation results are in accordance with the law of production history.The shear stress concentration near the fault and the shear force of the casing is larger in the block of S142;in the block of S177,there is a large displacement between the mudstone layer and the non mudstone layer,and the creep of the mudstone leads to the increase of the casing shear stress with the water injection.A theoretical basis for the fluid solid coupling analysis of casing failure in oil field is provided in this study,and it has a very important significance for analysis of casing failure and prevention and control for casing.