某井N80鋼級套管脫扣和粘扣原因分析

Analysis of Causes for Thread Jump-out and Galling of N80 Casings as Used in One Oil Well

摘要: 對某井Φ139.7 mm×7.72 mm N80鋼級長圓螺紋套管脫扣和粘扣事故進行了詳細的調查研究。分析認為套管發(fā)生脫扣的原因主要是由于下套管上扣時螺紋接頭發(fā)生嚴重粘扣,使其連接強度大幅度降低所致。該井井口中心與管柱軸線偏離較多,且采用鉆桿液壓鉗下套管,在上扣過程中套管接箍嚴重夾持變形,外螺紋接頭與嚴重夾持變形的接箍上扣配合之后導致套管嚴重粘扣損壞。套管嚴重粘扣還與套管本身抗粘扣性能差有一定關系。

Abstract: In-deep investigation and studies are made into the failures of long round thread jump-out and galling of the Φ139.7 mm ×7.72 mm N80 casing as used in one oil well.It is identified through the analysis that the main cause for the said casing thread jump-out is the serious galling of the thread connection as occurred in the make-up process of the casing,during casing running operation,which leads to the connection strength is tremendously reduced.The wellhead center offsets the casing string axis too much,and the coupling is seriously deformed during the make-up process due to clamping with the hydraulic drill pipe jaws.As a result,the matching between the pin and box gravely deformed coupling causes the galling damage of the casing connection.Moreover,the galling of connection is also related to the poor galling-resistance of the casing itself.