泾河油田延安组煤层特性与井壁失稳机理

Characteristics and Instability of Yan'an FormationCoalbeds in Jinghe Oilfield

泾河油田在钻井过程中延安组煤层发生井壁失稳问题。通过对泾河油田延安组煤岩特性分析,应用井史与测井资料分析煤层井壁失稳情况,得出泾河油田钻遇煤层井壁失稳主要表现为井塌,约三分之一煤层发生中等与严重井塌,平均井径扩大率超过10%。最终证明,泾河油田延安组煤层失稳情况不是很严重,大部分煤层段为性状稳定的暗煤,一般井壁稳定性高;而失稳煤层段主要因为钻井液封堵性能不足导致割理、裂缝发育煤层和含泥岩夹层的劣质煤层坍塌。

In drilling the Yan'anFormation(coalbeds) in Jinghe Oilfield,borehole instability has long been a problem.Analyses of the drilling and wireline logging data show that one third of the coalbeds have been moderately or severely collapsing during drilling,with average hole enlargement over 10%.It has been found that,the Yan'anFormation as a whole does not destabilize badly,most of the coalbeds are dull coals,which are generally stable and do not collapse.The collapse of the coalbeds during drilling has been caused by the lack of plugging and sealing capacity of the drilling fluid used,and the existence of fractured coalbeds and poor quality coalbeds with mudstone interlayers.