The Effects Of Casing Wear On Safety And Reliability Of Casing String In Deep Wells

In recent years, the number of deep wells is increased greatly,casing wear is cased by drilling pipe that is already laid down the wellbore, usually a import problem during the drilling of deep well. How to predict the wear area and the residual intensity for the casing wear has great importance for the safety and reliability of casing in the deep well.The paper get the caculated method on the basis of an well developed model, wear- efficiency model which is developed by White and Dason ,through making definite the reason and mechanism on the casing wear. make the caculated method clearly on the main parameters in the model then obtain the wear area. At the same time, the result of maximal wear depth.of crescent shaped wear casing could be got by using the geometric relationship and the wear area,. The residual intensity of this paper mainly contain two parts: residual collapsing strength and residual internal pressure strength. According to the difference in the load distribution on the casing's external wall, the analysis on residual collapsing strength is divided into two segments: uniform external pressure and heterogenetic external pressure. In the former part, the paper is given a modified empirical formula, considering the casing wear as one of flaws in the casing itself. Comparing with other formulas, this formulas has a better calculation accuracy. In the latter part, as the heterogenetic external pressure couldn't use the empirical formula directly. The author derive an formula to transform the heterogenetic external pressure to uniform external pressure. In order to analysis residual internal pressure, this paper is given a"slotted ring"model to derive formula, and modify the formula with the finite element numerical calculation.On the base of mechanical calculate model and the load analysis during well drilling, analyze"well Shengke 1"by the programming Matlab, according to the well structure and operational parameter to calculate the maximal wear depth, residual intensity and safety factor of residual intensity for full hole casing, get the relationship with the well depth, find out the dangerous points, then analyze the safety and reliability of casing string during casing strength design and construction. the design safety facor of wear casings, then compare give an allowing wear depth, give a reference in casing strength design of deep well.