超深井井壁稳定性分析

WELLBORE STABILITY OF ULTRADEEP WELLS

超深井钻井过程中存在多套地层压力体系,井壁稳定性条件复杂,高温、高压、深部地层岩石可钻性差等难点。随着井深的增加,地层压力梯度急剧增加,需要较高密度的钻井液来平衡地层压力。超深井的裸眼井段较长,钻井液浸泡时间长,容易导致岩石抗压强度软化,尤其一些泥岩层段,一旦被钻井液浸泡过后,井壁极易发生失稳。在超深井钻井过程中,不同的温度差异必然导致近井壁岩石应力分布发生改变,影响井壁稳定性。为此,提出分别利用地震、测井数据得到的坍塌破裂密度曲线来预测超深井井壁稳定性,所建立的计算模型应用于莫深1井的井壁稳定性分析,结果表明:预测情况与工程实际吻合。

Challenges like multiple sets of formation pressure system,complicated wellbore stability conditions,high temperature,high pressure,low rock drillability in deep formations exist in ultradeep well drilling.With the increase of well depth,the formation pressure gradient goes up sharply,higher drilling fluid density is required to balance formation pressure.And the openhole section in ultradeep wells is often longer,the time soaked by drilling fluid is longer,the rock is easier to become softened,especially when drilling through the shale formations the wellbore is easier to collapse after soaked in drilling fluid.Therefore the temperature differential will certainly cause the change of stress distribution in near-wellbore rocks during ultradeep well drilling and ultimately result in wellbore instability.In this paper,seismic and logging data was used to produce collapse-fracture density curve for predicting the wellbore stability of ultradeep wells,from which the calculating model was established to analyze the wellbore stability of the well Moshen-1,and the results match the actual parameters on fields.