Liuhua11-1Oilfield Casing Failure Analysis And Countermeasure

Development of the oil well casing damage during the latter part of oil field development is a serious problem facing the serious impact of oil field production efficiency. Casing damage caused by a variety of reasons, such as acid gas corrosion, casing wear and erosion of sand fluid. Liuhua11-1oilfield casing for damage to the actual situation, this theoretical analysis, we explore the mechanism of casing damage, to make technical measures, to address the Liuhua11-1oilfield casing damage problems from the theoretical basis and technical support.Oil into the casing corrosion and external corrosion of corrosion. Outside the external tube corrosion is mainly soil erosion and groundwater suffered corrosion and stray current corrosion-and macro-cell corrosion; the corrosion inside the tube is mainly caused due to internal corrosion media. Corrosion of oil and gas wells has three salient features:(1) gas, water, hydrocarbons, solid particles exist in multiphase flow corrosive medium;(2) high temperature and/or high-pressure environment;(3) H2S, CO2, O2, Cl-and water is the main corrosive oil and gas wells.The main production casing wear during drilling. Drilling, drill string rotation to the casing wall surface area by the circumference of the friction, the drill string and the vertical feed, the lower the surface by drilling the casing wall friction axial direction, drilling the drill string under pressure bending deformation and the transverse vibration of the drill casing and drill string in the local areas (such as drill pipe joints, stabilizer, etc.) contact, the contact area have a greater contact pressure, so the casing will have a greater wear and tear. While drilling, drilling fluid circulation to carry large amounts of debris through the annulus, casing and drill string in a large number of abrasive contact area to enter, so the casing is mainly abrasive wear, wear fast. Touching the contact pressure on the casing wear have a great impact, as the contact pressure increases, the greater the wear rate of the casing. When the contact pressure reaches a high value, in addition to abrasive wear, but also accompanied by the occurrence of adhesive wear.Many factors affect the casing wear can be divided into external factors and internal factors. External factors that the working conditions of wear, including load, speed, temperature, relative motion and the stress state, abrasive, media and environmental factors; internal conditions include the chemical composition of materials by grinding, and mechanical properties.Contact between the friction material is worn surface as a result of relative motion, the contact stress under the surface damage caused material loss process. Casing wear occurred is a prerequisite for casing and drill pipe tool joints between the contact and friction effects. From the casing and drill pipe tool joints, and the interaction between the working conditions of view, there may be oil and gas well casing are the main wear mechanism of abrasive wear, adhesive wear, corrosion, wear, fatigue wear and erosion.In this paper, Liuhua11-1oil field is located130sea miles southeast of Hong Kong, where the water depth of about300meters, was discovered in1987, is the eastern South China Sea’s largest oil reserves. This paper analyzes the Liuhua11-1oil field development layer temperature, CO2and H2S partial pressure, Cl-and other corrosive environments. ECE software used to predict the corrosion environment, forecasting results show that the use of carbon steel tubing and casing failure2-3years; According to the literature produced severe corrosion data partition map, the field of corrosion of carbon steel tubing and casing perforation likely.Liuhua11-1oilfield corrosion characteristics of the design of the targeted environment simulated experiment (a total of234times), and corrosion rate obtained with the variation of different factors; under the well trajectory, BHA and other drilling data calculated casing wear during drilling section, determine the maximum wear at the location, and put forward recommendations to prevent excessive erosion;CO2/H2S coexistence environment of research shows that:in the partial pressure ratio of5:1<CO2:H2S<2000:1case, CO2corrosion is inhibited, no pitting of carbon steel; but in the CO2:H2S=1:1When compared with pure CO2have increased corrosion, pitting corrosion is more serious; Liuhua11-1oil fields mainly in the partial pressure less than the interval; conclusions based on galvanic corrosion perforation repair materials proposed mining under the remaining life of the N80,1Cr,3Cr three types of materials selection; the comprehensive consideration of abrasion, corrosion and sand on the basis of the situation, analyzed and found four damaged the main reason for the well perforation; predict the service life of the casing is not damaged: separate CO2corrosion computing (This is most the most serious corrosion),40lb/ft of steel casing3years because there is pitting appears casing perforation;1Cr casing life:8.6years,3Cr sets of life of15.3years. Wells on the high content of H2S (partial pressure ratio of CO2:H2S is less than5:1), recommended3Cr-S material.