基于抛物线强度准则的泥页岩井壁稳定性分析  

ANALYSIS OF THE WELLBORE STABILITY IN MUD SHALE FORMATIONS BASED ON THE PARABOLIC STRENGTH CRITERION

作　　者：丁乙[1] 刘向君[1] 罗平亚[1] 梁利喜[1] DING Yi;LIU Xiangjun;LUO Pingya;LIANG Lixi(State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University,Chengdu 610500,China)

机构地区：[1]西南石油大学油气藏地质及开发工程国家重点实验室,四川成都610500

出　　处：《大庆石油地质与开发》2018年第5期160-167,共8页Petroleum Geology & Oilfield Development in Daqing

基　　金：国家自然科学基金项目"富有机质硬脆性页岩水化机理基础研究"(41772151);国家重大科技专项"测井工程应用软件包研发"(2011ZX05020-007-06);四川省应用基础研究计划项目"形成大规模压裂缝网的水平井井眼轨迹优化研究"(2014JY0092)

摘　　要：泥页岩地层井壁垮塌现象频发,其主要诱因在于泥页岩的强水化特性。由于水化作用影响,泥页岩与钻井液接触后,力学强度将发生明显改变。准确预测不同钻井时间下的泥页岩强度是保持井壁稳定性的基础。通过室内实验,对钻井液作用下的泥页岩力学特性进行分析,在此基础上,对适用于泥页岩的强度准则进行探讨,分析认为:针对一定力学性质的泥页岩,采用不同强度准则得到的岩石破坏应力具有明显差异,因此强度准则的优选具有必要性。在原状地层条件下,采用抛物线型与直线型强度准则对三轴实验数据进行拟合,结果显示两者的拟合值都与实测值吻合较好。然而随着钻井液作用时间增加,针对受明显水化作用的泥页岩,两者拟合趋势线出现显著差异,实测数据逐渐倾向抛物线型趋势线。因此,基于抛物线强度准则,考虑水化作用对泥页岩强度影响,建立泥页岩地层坍塌压力预测方法并分析地层井壁稳定性,结果表明:基于抛物线模型得到的坍塌压力随井眼轨迹、地应力和钻井时间的变化趋势与常规模型的计算结果一致,但预测安全钻井液密度有所差异。随钻井时间增加,该差异值逐渐增大。通过现场实例分析证明:基于抛物线强度准则的井壁稳定模型能更准确预测泥页岩地层坍塌压力,且与油田现场数据具有较好的对应性,从而证明该模型在泥页岩地层钻井工程中的适用性。The phenomena of the wellbore collapse occur frequently for the shale formation,the central inducing reasons are the strong hydration characteristics of the mud shale. Due to the influence of the hydration,after contacting between the mud shale and the drilling fluid,the mechanical strength will change obviously. Accurately predicting the strength of the mud shale in different drilling time is the basis of maintaining wellbore stability. With thehelp of the indoor experiment,the appropriated strength criteria for the mud shale were explored,the analysis shows that in the light of a certain mechanical properties,there are obvious differences in the obtained rock failure stress by means of different criteria; therefore it is necessary for the optimization of the strength criteria. Under the condition of the initial formation,the parabolic and straight line strength criteria were adopted to match the triaxial experimental data,the fit results show that there exists much better accordance between the matching and actual measured values. But with the increase of the acting time of the drilling fluid,for the mud shale under the obvious hydration,there is remarkable difference between the trend lines of the two matches,the actual one is gradually close to the parabolic trend line. Therefore,based on the parabolic criterion,considering the influence of the hydration on the mud shale strength,the predicting method of the collapse pressure of the mud shale formation was established,and moreover the wellbore stability of the formation was analyzed. The result shows that comparing with the calculated result,there is good consistence for the changed trends of the collapse pressure obtained by the parabolic model with the wellbore trajectory,in-situ stress and drilling time,while there is a certain difference in the predicted safe drilling-liquid density. With the rise of the drilling time,the difference value gradually increases. The analysis of the field case indicates that the wellbore stability model based on the parabolic

关 键 词：泥页岩地层 水化作用 抛物线强度准则 井壁稳定 

分 类 号：TE355.5[石油与天然气工程—油气田开发工程]