硬脆性地层井眼失稳剪切破坏程度定量预测
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摘要
钻井过程中,硬脆性地层的井壁失稳的主要形式为剪切破坏(坍塌或掉块)。由传统的井壁失稳力学模型设计出的钻井液密度值偏高,不利于提高钻井速度和降低钻井成本。然而,实钻过程中井眼往往存在一定的井径扩大现象,并产生一定程度的坍塌掉块而不会发生井壁失稳和井筒复杂事故。为此,有必要建立硬脆性地层井壁失稳程度的定量预测模型。根据硬脆性地层井壁破碎前仅出现弹性变形的特征,基于线弹性理论,推导出直井的井壁围岩应力模型,建立了井壁失稳(剪切破坏)程度与地应力、孔隙压力、岩石力学参数、井筒液柱压力之间的定量关系,并对主要影响因素进行了敏感性分析。对比实例井的实测数据,该模型计算结果与实钻情况一致,具有很好指导意义。
The principal instability form of hard-brittle formation is shear failure during oil & gas drilling. For this kind of formations,the mud density to maintain borehole stability computed by traditional method is usually higher,which can reduce the drilling rate of penetration to some extent. During actual drilling,the down hole complex can't occur unless wall rocks collapse on a large scale. Therefore,it is very important for reasonable mud density designand safe quick drilling to establish a new wall rock shear damage prediction model for hard-brittle formations. A vertical well circumferential stress mathematical model is deduced on basis of characteristics of hard-brittle formations and linear elastic theory. The characteristic of hard-brittle formations is that before breaking only elastic deformation occurs without plastic deformation. This model has established a quantitative relationship between shear damage degree( thickness of collapsed zone and collapse angle) and ground stress,pore pressure,mechanics properties of rocks and drilling fluid hydrostatic pressure. Sensitivity analysis on main factors is also carried out. The calculation results of the theoretical model coincide with the measured data,which shows the model provides high accuracy prediction.
The principal instability form of hard-brittle formation is shear failure during oil & gas drilling. For this kind of formations,the mud density to maintain borehole stability computed by traditional method is usually higher,which can reduce the drilling rate of penetration to some extent. During actual drilling,the down hole complex can't occur unless wall rocks collapse on a large scale. Therefore,it is very important for reasonable mud density designand safe quick drilling to establish a new wall rock shear damage prediction model for hard-brittle formations. A vertical well circumferential stress mathematical model is deduced on basis of characteristics of hard-brittle formations and linear elastic theory. The characteristic of hard-brittle formations is that before breaking only elastic deformation occurs without plastic deformation. This model has established a quantitative relationship between shear damage degree( thickness of collapsed zone and collapse angle) and ground stress,pore pressure,mechanics properties of rocks and drilling fluid hydrostatic pressure. Sensitivity analysis on main factors is also carried out. The calculation results of the theoretical model coincide with the measured data,which shows the model provides high accuracy prediction.
引文
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[2]Moos,D.,S.M.Willson,and C.A.Barton.Impact of rock properties on the relationship between wellbore breakout width and depth[C].Proceedings of the 1st Canada-U.S.Rock Mechanics Symposium,Vancouver,Canada,27-31 May 2007:1677-1683.
[3]王金凤,邓金根,李滨.井壁坍塌破坏过程的数值模拟及井径扩大率预测[J].石油钻探技术,2000,28(6):13-14.
[4]马克D.左白科.储层地质力学[M].北京:石油工业出版社,2012:204-209.
[5]钟敬敏,齐从丽,王希勇,等.钻井动态坍塌压力探讨[J].钻采工艺,2012,35(5):11-14.
[6]刘玉石,白家祉,周煜辉,等.考虑井壁岩石损伤时保持井眼稳定的泥浆密度[J].石油学报,1995,16(3):123-127.
[7]陈勉,金衍,张广清.石油工程岩石力学[M].北京:科学出版社,2008:118-121.
[8]李士斌,窦同伟,董德仁,等.欠平衡钻井井底岩石的应力状态[J].石油学报,2011,32(2):329-334.
[9]刘之的,夏宏泉,张元泽,等.地层坍塌压力的测井预测研究[J].天然气工业,2004,24(1):57-59.