The Study Of Casing Failure Mechanism Numerical Simulation

According to the survey to water-oil wells'casing failure and casing failure mechanism study all over the world, we can acknowledge from this paper that during the oilfield development, the operational environments of oil-water well deteriorate increasingly with the longer production hours and continuous actualization of development projects, especially the actualizing of water flooding and polymer flooding. Casing failures are already international general problems and casing failures speed is increasing with years. The total casing failure ratio waves from several percent to 20-30 percent. The casing failure ratio in certain local area is as high as 70-80 percent. Up to the end of December 2005, accumulative total 11188 wells with casing problems had been found in Daqing oilfield. This number is 18.54 percent to water-oil wells which are now on stream. Every six wells which were on stream that one well would be damaged.For many years, domestic and foreign oilfield, scientific institution, colleges and universities have done masses of work on casing failure mechanism, and have summarized some casing failure mechanism scientific payoffs. E.g. strata settlement theory: a stronger tectogenetic movement in the area arose by a mass - production petroleum and underground depletion appearance make water-oil wells deformative. Mudstone expansion theory: water immerging mudstone strata from tiny crack make mudstone strata creep and mass deformative wells are appeared. But these theories develop from the points of determining the nature, part and single technology. These theories can't satisfy oilfield's needs over the questions of instructing and resolving the oilfield casing failure. Casing failure rate is running to fast. In order to deepen the study of casing failure mechanism and protective measures, carrying the study on liquid-solid coupling on ration and numerical simulation study from overall situation and system will offer theory gist to ultimately solve the problem of casing failure protection.The subjects involved in this paper are rock mechanics, fluid mechanics in porous medium, theory of elasticity and plasticity, reservoir physics, non linear finite element analysis, and so on. Constitutive relation of rock is also to be studied. The numerical simulation study of casing failure mechanism has commanding theory sense. This paper builds the mathematical model by studying effect to casing failure brought by liquid-solid coupling, injection-production, working, geologic condition. Reducing the virtual seeking for answer and realizing the breakthrough of this theoretic equation from theoretical investigation to technical application by studying the saturation two-phase fluid flow, pore medium deformation coupling.This paper carries a history matching of injection-production by studying the leading area of the middle block of North 1 area locating in oil product No.1 of Daqing oilfield. Coincidence rate of wells in calculation to wells in actual is 83.3%.A result educed by computing is the casing failure will appear if casing Mises stress increases 17～35 MPa or casing Mises stress reach 300 MPa. Raising or reducing pressure of water-oil wells, the stress acting on casing will change correspondingly. The Mises stress acting on water-oil wells casing concern bottom hole pressure very nearly.Grid method is put forward firstly in this paper and is continuing to improve in study. Applying of this advanced technology will make mass analyzing-computing possible. Total calculated girding number the middle block of North 1 area is 670,134 and node number is 713,416. More data can be calculated and this function is unexampled compared with other finite element softwares.