磨损套管抗挤强度的新算法研究

MEW ALGORITHM OF COLLAPSING STRENGTH OF WEARING CASING

油气井钻井过程中,由于钻具和套管相互摩擦,造成套管内壁磨损并引起磨损套管抗挤强度降低,直接后果是:降低油气井寿命,严重时将导致某段油气井报废或整口油气井报废。因此,套管柱设计尤其是水平井、大位移井、深井、超深井钻井必须考虑磨损对抗挤、抗内压强度的影响,而现有计算方法在计算磨损套管抗挤强度时通常忽略了制造缺陷对挤毁强度的影响,计算值与实测值差异较大。为此,文章研究了磨损套管的挤毁机理,认为计算磨损套管的抗挤强度应重点考虑磨损对抗挤强度的影响,同时考虑制造缺陷对套管抗挤强度的影响。基于此,文章进行了大量研究,应用叠加原理,建立了计算磨损套管抗挤强度的新算法。通过对此算法和其它算法的计算结果与试验数据比较分析表明,新算法优于其它算法并与试验数据更接近,能较好满足工程要求,为磨损套管柱设计提供了理论依据。

In the process of drilling oil and gas wells, the casing inwall wear will happen owing to the friction between drill string and casing, thus reducing the collapsing strength of wearing casing, which direct consequence will be the decrease in oil/gas well servoice life, more serious, will lead to the well’s being partially or wholly abandoned. Therefore it is necessary to consider the effect of wear on the collapsing and internal pressure strengths in casing design,especially in the casing design for horizontal well, extended reach well, deep well or ultra-deep well. However, the effect of manufacturing defects on collapsing strength was always neglected in calculating the collapsing strength of wearing casing by the existing methods, which leaded to a great difference between calculation values and test data. For this reason,through investigating the collapsing mechanism of wearing casing it is pointed out that the two effects should be all considered emphatically.On the basis of carrying out a great deal of works, a new algorithm of calculating the collapsing strength of wearing casing was set up by use of superposition principle. Through analyzing and comparing the the new algorithm with the other algorithms and the test data, it is indicated that the new algorithm can meet the needs of engineering, being much better that the other algorithms and closer to the test data, thus providing a theoretical basis for wearing casing design.(Financed by the National Natural Science Foundation project, No.50074025)