Calculation Of Casing Wear Shape And Prediction Of Residual Strength Under Compound Mode

Casing wear refers to the complex situation that the drill string wears the inner wall of the casing for a long time in drilling operation,resulting in the thinning of the casing wall thickness and even wearing through the casing.It widely exists in complex oil and gas well projects such as deep wells,horizontal wells and extended reach wells.Casing wear will reduce casing strength,lead to integrity failure such as casing rupture and flattening,and even lead to safety accidents and serious economic losses.Therefore,establishing accurate casing wear shape and depth prediction model and optimizing reasonable anti-wear measures are the key contents of casing wear research in complex oil and gas wells.The field measurement data show that there are many wear areas on the casing in some well sections,and the wear shape presents more complex compound modes than the single crescent mode.Besides,the failure behavior of casing internal pressure and external pressure under compound wear modes is complex,and the failure mechanism needs to be revealed,which are beyond the scope of conventional models.To solve these problems,the prediction of casing wear shape and the calculation of casing residual strength under compound modes are carried out.Firstly,based on the measured casing wear shape data,three typical compound wear modes are found,the mechanical mechanism of the formation of the compound wear mode is revealed,and the calculation model of casing wear shape and depth under the compound mode and the corresponding algorithm are established.Then,based on experimental results and numerical simulation results,the failure mechanism of compound worn casing under internal pressure and external pressure is revealed,the main controlling factors and action rules of casing residual strength are revealed,and the intelligent prediction method of worn casing residual strength is constructed and its accuracy is verified.Finally,based on the above theories,the calculation software of casing wear depth and residual strength is developed,and the engineering application research is carried out.The results show that the casing wear shape is not always a single crescent,but the compound modes of multi crescent overlapping,crossing and separating.Different wear modes are caused by different reasons.The reason of overlapping is the change of wear outer diameter,the reason of crossing is the small deviation of wear position,and the reason of separating is the large deviation of wear position.The internal pressure failure of the worn casing is a kind of strength failure.When the equivalent stress in the middle of the casing wall in the main wear area reaches the yield strength of the material,the internal pressure failure occurs.Casing external pressure failure is a kind of stability failure.When the ovality of casing section reaches the critical value,the external pressure failure occurs.The above research breaks through the limitations of the classical single crescent wear mode,and is consistent with the field measurement and experimental results.