气体钻井突发性井壁失稳动力演化机理及试验研究

Dynamical evolution mechanism of sudden wellbore instability in nitrogen gas drilling and experimental research

从致密砂岩损伤破坏的角度出发，综合考虑致密砂岩的物理力学性质、地应力、裂缝圈闭高压等因素，在分析孔隙压力、地应力、裂缝圈闭高压在突发性井壁失稳过程中所起的作用基础上，将气体钻井突发性井壁失稳具有强烈时间效应的动态力学过程分为孕育、突变、井筒运移和终止4个阶段。对裂缝圈闭高压、地应力作用下致密砂岩的加速损伤演化引起的突发性井壁失稳机理进行了阐述，裂缝圈闭高压是突发性井壁失稳的主要动力源，地应力对突发性井壁失稳起辅助作用。通过模拟实验表明，受地应力破坏后的致密砂岩岩体在有裂缝情况下，卸压初始时刻释放的能量是无裂缝时的5～10倍，且该能量与动力学失稳密切相关。

Considering the damage and the physical mechanical properties of tight sandstone ,ground stress ,fracture trap high pressure ,based on the analysis of the effective of pore pressure ,ground stress and fracture trap high pres-sure in the sudden wellbore instability process , sudden wellbore instability is dynamic process with a strong time effect which is divided into four stages：preparation,catastrophe,wellbore movement and termination.The article de-scribes the occurrence mechanism of sudden wellbore instability that caused by the accelerate damage evolution of tight sandstone because of the fracture trap high pressure and ground stress .the fracture trap high pressure is the main power source ,the ground stress only plays a supporting role in the sudden wellbore instability .The experi-ments show that release energy at the initial moment is 5～10 times when no crack in the core after the destruction of the tight sandstone ,and the energy are closely related to dynamic instability .