Research On Casing Collapse Resistance

Casing collapse resistance is a very active research field worldwide. API/ISOhas been organizing international cooperation research on it for many years. Thiseffort will result in the standardization and publication of new versions of API5C3and a corresponding ISO document, ISO 10400. A key effort to modernize API5C3has been focused on improving the predictive equations for collapse.This thesis summarizes the researches on casing collapse in the world. On thebase of API collapse pressure formulas, a new formula for the estimation of thecollapse resistance for casing has been put forward. The model and software havebeen verified by the test data coming from Tubular Goods Research Center andTianjin Pipe Corporation. Research shows that the model has great importance intheoretical research, field application, and casing manufacturing quality. At the sametime, API/ISO Collapse Sub-Team has compared the formula of this thesis withother related formulas according to hundreds of test data. The result shows that theformula of this thesis is of much better than the current API standard and as good asthe formula newly developed by API/ISO WG2B. As a result, I and my supervisorare invited to take part in the WG.The new formula of this thesis can also be used to calculate the collapseresistance for high collapse casing. Though a large number of high collapse casingsare used at present, they are non-API casings and their collapse resistances cannot beestimated with API collapse pressure formulas. In general, collapse resistance ofhigh collapse casing is about 30% higher than that of API casing which in the samegrade and size. It is useful for manufacturer to improve casing manufacturing qualityand for user to choose high collapse casing. For example, among the factors thateffect casing collapse resistance, residual stress is a remarkable item. This is theright reason why the collapse resistance of some high collapse casings made in ourcountry is lower than that imported from other countries, even though they are in thesame grade and size precision.In addition, this thesis has examined how non-uniform loading affects casingcollapse resistance and an important conclusion has been obtained that it is moreeffective to increase casing wall thickness than to increase casing steel grade undernon-uniform loading conditions. We suggest that extra-heavy casing is an effectivemethod to prevent casing from collapsing under non-uniform loading. We also putforward extra-heavy casing size series and give advice to manufacturer on reducingmanufacture difficulty and cost. This provides a theoretical basis for the research oncasing collapse under non-uniform loading.This thesis takes the assumptions of salt rock submitting to the behavior ofviscoelastic model, and both initial earth stress and Poisson's ratio not varying withtime. According to logging information, a method for the back analysis of salt rock'screep parameters has been set up. The method has been applied and verified.Research shows that modern back analysis theory of rock-soil engineering has thesuperiority of more dependability and less cost to surface core testing indetermination of salt rock's creep parameters. This is the most reliable, mostadvanced and simplest method at present. So back analysis theory has greatimportance in both theoretical study and field application.The main innovation of this thesis is that a new formula for the estimation ofthe collapse resistance for casing has been put forward. This makes me and mysupervisor invited to take part in API/ISO Collapse Sub-Team. Through theinternational cooperation research, I have got a lot of information and many differentresearch methods. I have also mastered the international research development.Whether the research in this thesis or part of it will be adopted by API/ISO stillneeds further research and international exchange.