三向应力状态下层理性泥页岩地层井壁稳定性研究

Well Stability Study for Laminated Mud Shale Formations in Three-stress State

层理性泥页岩地层钻进过程中,极易发生井壁失稳问题,严重影响了钻井作业效率,增加了勘探开发的成本。探索了层理性泥页岩地层的井壁失稳机理,开展了考虑钻井液作用下层理性泥页岩地层在真实三向应力状态下的井壁稳定性预测模型研究。研究表明:忽略中间主应力的影响不能准确预测层理性泥页岩地层坍塌的风险;钻井液滤液沿层理面的渗流会降低层理面的黏聚力和内摩擦角;并随时间的变化显现出快速降低和平缓降低两个阶段;改进的层理性泥页岩地层井壁稳定性分析模型能够真实反映地应力状态和井壁岩石的力学特性,现场应用表明其能够比较准确的预测层理性泥页岩地层的井壁稳定性。

Well stability is very common in laminated mud shale formations which are caused by bedding parallel weak planes,which affects seriously the efficiency of drilling and increases the cost of exploration and development. The mechanism of well stability in laminated formations is researched,and studied the wellbore stability model considering the interaction between the drilling fluid and formation in three-stress state. Results show that ignoring intermediate principal stress will not accurately predict the collapse risks in laminated mud shale formations.The interaction between drilling fluid and formation will reduce rock cohesion and internal friction angle,and showing two stages of quickly decline and gently decline. The new wellbore stability model can truthful reflect the stress state and rock mechanical properties,and field application shows it can accurate to predict wellbore stability of laminated mud shale formations.