受套管磨损约束的深井钻井延伸极限预测模型

深井超深井的套管磨损问题十分严重，严重制约了深井超深井延伸极限的增加。为了提高深井超深井的延伸极限，需要研究深井超深井套管磨损和延伸极限的关系，并明确建立以套管磨损为约束条件的深井延伸极限模型。建立了套管磨损能量方程，基于套管磨损截面几何方程，引入套管截面磨损深度极限值，并考虑井下管柱在钻进过程中的载荷传递，采用迭代法反演出深井超深井在套管磨损条件下的延伸极限值，结合塔里木某超深井的数据资料进行实例计算，并通过和该井的井径测试数据进行对比，验证模型的合理性。研究结果表明，实测该塔里木超深井3 070 m处套管磨损最严重，磨损量为3.15 mm，将其代入建立的套管磨损延伸极限模型中，可得到该井的磨损延伸极限为7 812 m，这与该井实际井深7 500 m极为接近，验证了本文模型的合理性。该研究从套管磨损理论的角度，预测了深井超深井的延伸极限，并为深井超深井的安全作业和钻具选型提供了理论依据。

A model for predicting the extension limit of deep and ultra deep well under the constraint of casing wear

The casing wear in deep and ultra deep wells is so serious that the increase of the extension limit of deep and ultra deep wells is restricted. In order to improve the extension limit of deep and ultra deep well, it is necessary to study the relationships between the casing wear and the extension limit of deep and ultra deep wells and definitely establish a deep-well extension limit model under the constraint of casing wear. In this paper, the energy equation of casing wear was established. Then, based on the geometric equation of casing wear section, the extension limit of deep and ultra deep well under the condition of casing wear was inverted by means of iteration method by introducing the wear depth limit of casing section and considering the load transfer of downhole string in the process of drilling. Finally, case calculation was carried out based on the data of a certain ultra deep well in Tarim. In addition, the rationality of the model was verified by comparing the calculation result with the caliper test data of the case well. According to the actual measurement result, the casing wear at the depth of 3 070 m in the case ultra deep well is the most serious with the wear loss of 3.15 mm. When this value is put into the proposed extension limit model under the constraint of casing wear, the calculated extension limit of the case well is 7 812 m, which is quite close to its actual well depth (7 500 m). It is verified that the proposed model is rational. The research results predict the extension limit of deep and ultra deep wells and provide theoretical basis for the safe operation and drilling tool type selection of deep and ultra deep wells from the perspective of casing wear theory.