Study On Safety Risk Of Casing Pipe Production Based On Corrosion Test And Life Prediction

Casing damage severely hampered the normal production of oil and gas fields, andin the oil and gas exploitation at home and abroad has become a one of the importantproblems needed to resolve. Because of the complexity of the oil and gas Wells andgeological conditions, and the most used conventional design method of casing design,so difficult to find a effective method of preventing casing damage, tend to be in to takeremedial measures after the casing damage is (casing or drilling instead of maintenance),this not only needs huge investment, and the effect is not good. For a long time, isgenerally believed that the cause of casing damage factors can be roughly divided intogeological and engineering factors, development factors, the corrosion factors of fourcategories. Among them, the corrosion factors caused the decrease of strength of casingdamage accident. So the damage of casing corrosion mechanism and corrosioncondition in the actual casing use monitoring forecasting has important theoreticalsignificance and practical value.The first production area of a shale gas field in Southwest China is the supportproject in this thesis, in view of the casing for production of security risks, consideringthe specific production process and characteristics of the shale gas well, based on theresearch at home and abroad, through systematic analysis and research of complex wellconditions of various factors and the mechanism of casing corrosion damage, design afeasible field coupon tests, the method of study of shale gas well casing corrosion andwear, on this basis, through mathematical method to predict casing corrosion rate of theshale gas well, and then to evaluate the safety and service life of casing and predictions.Paper main work and results are as follows:（1）The corrosion cause of casing damage are classified analysis, mainly analysesthe acid, salt material, hydrogen sulfide, bacteria and the influence of wear of casingcorrosion. This paper introduces the uniform corrosion and local corrosion of two kindsof commonly used casing corrosion and corrosion rate prediction model. Of CO2concentration, flow velocity, temperature and chloride ion, carbonate ions, sulfuric acidroot ion calcium and magnesium ions on the influence law of casing corrosion and itsmechanism are analyzed, and to predict the service life of the casing and the safetyevaluation provides the basis. （2）Project in filing district of shale gas field focal dam block, shale gascomponents, and water quality, water pressure and temperature output, well borestructure and design of various aspects, such as casing is analyzed, for the design of thefield coupon tests and casing life prediction provides the basis. Analysis showed that:1)the shale gas components and formation of CO2out of the water content of cationic (Ca2+, Mg2+) and anion (Cl－、HCO3、SO24) content will affect casing corrosion situation;2)project, casing completion of well bore structure was used in the production casing withdiameter of139.7mm, material for TP110T, casing wall thickness of12.34mm.（3）In order to objectively and accurately analyze filing shale gas coke dam blockshale gas well corrosion condition, this paper designed a feasible site coupon testmethod, that is, from already was choose n Wells of25Wells for coupon test research,and then by mathematical method and computer technology to analyze test data, testresults are generalized to other did not test well.（4）Coupon test process, monitoring the corrosive factors, such as temperature,velocity, pressure, and to measure the CO2concentration and different test Wells invarious cat ions (Ca2+,Mg2+) and anion(Cl－、、) content, multiple regressionanalysis and neural network is adopted to improve the quantitative relationship ofmathematical fitting, get quantitative relationship of various kinds of influence factorsand corrosion rate. From the perspective of engineering safety, determine the variousinfluence factors of different stages could reach the worst value, calculate thecorresponding phase of the possible maximum corrosion rate. According to thecorresponding corrosion rate and corrosion time, then you can assess the casingcorrosion damage level, and to predict corrosion life and residual strength of the casing.