Prediction On Casing Wear And Residual Strength Analysis Of Wear Casing

In the deep and ultra deep wells, the problem of casing wear is increasingly prominent, has became a serious problem in deep well and ultra deep well drilling. Because of the wear of casing, its strength reduce sharply, cannot up to the original design of the casing, it affects the subsequent drilling and production operation. Therefore the accurate prediction of casing wear, and calculating the residual strength of worn casing accurate, is of great significance to drilling engineering and production operation. This paper had researched the subject about casing wear, facing the existing problems of related technology at home and abroad. Research contents include:Through the analysis of the worn casing under different drilling conditions, discussed the mechanism of casing wear, casing wear is mainly adhesive wear, abrasive wear, corrosive wear, fatigue wear, they translation in different conditions. Analysis of the influence factors of condition of drilling, BHA, dogleg degree, the property of drilling fluid and casing/drilling pipe materials on the casing wear. Using the model which based on energy transfer efficiency predict the wear of casing. This paper focuses on the analysis of the method to determine the efficiency of casing wear model. Using the tribology to analyze the friction between casing and drill pipe joint, a formula is derived to calculate the casing wear efficiency theoretically, which verified the relationship between efficiency and the contact force, wear time. This paper using geometry knowledge, deduced the crescent shaped wear casing wear depth calculation formula is more simple.The simulation of wear casing stress distribution was carried, by using finite element simulation, and found the mechanism of wear casing failure under the inner and outer pressure. This paper had discussed the influence to the remaining strength, which caused by wear depth, wear radius, original wall thickness of wear casing and casing diameter, and built the concept of stress concentration coefficient in wear casing, and got stress concentration coefficient formula by using statistic. This paper raised yield strength calculation formula which considered the stress concentration, the residual collapsing strength of wear casing with high precision.This paper had discussed the wear of each layer of the pipe in 4 typical casing programs, which provided a certain basis for the design of casing string in typical casing program. Through the analysis of a large number of examples of reduce of wear casing, the recommended safety coefficient of each layer casing: surface casing safety coefficient of anti-internal pressure 1.00~1.05, safety coefficient of anti-external pressure 1.05~1.10; the first technical casing safety coefficient of anti-internal pressure 1.05 ~ 1.10, safety coefficient of anti-external pressure 1.10 ~ 1.15; the second technical casing safety coefficient of anti-internal pressure 1.05~1.10, safety coefficient of anti-external pressure 1.05~1.10; the third technical casing safety coefficient of anti-internal pressure 1.00~1. 05, safety coefficient of anti-external pressure 1.05~1.10.