套管柱在水平井弯曲段的可下入性

Tripability of Casing String in the Curved Interval of Horizontal Well

套管柱在水平井弯曲段随井眼弯曲产生较大的弯曲应力和受到较大的摩擦阻力，有可能产生强度破坏、密封失效、稳定性破坏而不能下入。下套管前应对套管柱通过弯曲段的可能性加以判断，其准则是：（１）下套管通过弯曲段时，套管柱在直井段的浮重应大于总摩阻；（２）弯曲应力与拉应力之和小于套管的最小许用应力；（３）在弯曲段套管柱不发生屈曲变形；（４）螺纹密封不应失效。经判断套管柱不能通过弯曲段时，可用不封固井底的完井方式（如裸眼完井及其变种形式）。

In the curved interval of horizontal well,great frictional resistance can be imposed on the casing string and result in great bending stress due to the bending of the hole.As a result, the casing possibly can't be tripped in because of strength distruction,seal failure or stability distruction.Before running casing,it is necessary that the possibility of casing running through the curved interval be determined according to following principles:(1)when casing run through the curved interval,the buoyant weight of casing string in straight well should be greater than the total frictional resistance;(2)the sum of bending stress and tensile stress is smaller than the minimum allowable stress;(3)there is no flexural deformation of the casing in the curved interval;(4)seal should not fail.If it is determined that casing string can't trip through the curved interval,such completion method as downhole non cementing should be adopted(for example,open hole completion and its transformed methods).