Research On The Constitutive Equation Of Mud-Rock And The Mechanism Of Casing Shear Failure

With the adoption of various strengthened oil-extraction measures,the working conditions of casings of oil and water wells have become more and more deteriorated;the failure of casings of well is one important problem in oil engineering. Casing failure brings about enormous losses of manpower,material resources and financial resources to oilfields. Researches on the mechanism of casing failure have both theoretical and engineering significance.Casing failure is a complex problem involved with geo-mechanics,solid mechanics,fluid mechanics,material strength and theories in some other fields. The data of casing-failed wells,which are collected from DaQing Oil Field,indicates that shear failures of casing of wells is very serious. The change of construction of reservoir compaction in oil-extraction which a is due to the unbalance of the crust stress fields and the creep and gliding of mudrock layer used water-injection techniques are the main reasons of casing failure. The mechanical property of mudrock in condition of water-injection. Researches on the mechanical property of mudrock in condition of water-injection,the constitutive equation are constructed and the mechanical mechanism of casing shear failure is an urgent task to be accomplished. Research items in this dissertation are as follows.1. Through investigation and analysis,that the change of construction of reservoir compaction and the creep and gliding of mudrock layer are the main reasons of casing shear failure is studied. The mechanical mechanism of casing shear failure and theory of constitutive equation of rock-soil mechanics are summarized,which is foundation of research in this dissertation.2. The mechanical property of mudrock in condition of water-injection is studied. That change of the nonlinear bulk strain is important character in condition of water-injection of mudrock. The nonlinear creeping constitutive equation of mudrock which influences bulk expanding is established.3. Mechanical models of reservoir hunch and the creep and gliding of mudrock layer are established. Using theory of fracture mechanics and through theoretic analysis and calculation,the distribution of strains and stresses is given,which illustrates in reason the mechanical mechanism of casing shear failure.4. Some practical measures to prevent casing failures in suit are reasonably interpreted and confirmed by the theoretical results in this dissertation. From theory,some measures and rationalizationproposal to prevent casing failures are put forward further.The casing failure is increasingly aggravated year by year and there are about 600 to 700 casing-failed wells or a loss of more than a hundred million Yuan in DaQing oil field every year. The research and exploration in this dissertation can serve as reference for solution of casing failure in oil fields.