塔中区块高温高压裂缝性气藏封堵层气蚀剪切失效机理

为了深入了解塔中区块高温高压裂缝性气藏封堵层失效问题, 基于储层特征和流体特性的深入分析, 结合封堵层微尺度物理结构特征, 对高温高压裂缝性气藏封堵层失效特征进行了研究, 提出了封堵层气蚀剪切失效概念, 构建了封堵层气蚀剪切失效的物理模型, 并借助颗粒物质力学和液桥理论, 对封堵层气蚀剪切失效过程进行了深入研究, 并基于反向气蚀原理, 开展了室内反向承压实验研究。研究结果表明, 裂缝性封堵层"气蚀剪切"失效作为一种气藏封堵层特有的失效模式, 其发生过程分为3个阶段: 气体扩散降黏破坏、气蚀剪切剥离破坏和气液置换错位剪切破坏; 正向承压6 MPa的统一封堵层, 对于不同属性的流体其抗剪切破坏能力不同, 当反向驱替流体由柴油转变为氮气时, 封堵层的反向承压值由原来的2.0 MPa(22 min)和2.5 MPa(30 min)分别减小到后来的1.5 MPa(10 min)和1.0 MPa(12 min), 综合抗剪切性能降低了约50%, 表明气体具有与液体不同的破坏能力和机制。 

Failure mechanism of cavitation-induced shear of the plugging layer in high-temperature high-pressure fractured gas reservoirs in the Tazhong block,NW China

To profoundly understand the plugging layer failure behavior of high-temperature high-pressure fractured gas reservoirs in the Tazhong block, the failure characteristics of high-temperature high-pressure fractured gas reservoirs were studied and analyzed based on the combination of reservoir characteristics, fluid properties and the microscaled physical structure of the plugging layer. The concept of cavitation-induced shear failure is proposed, and the physical model of cavitation-induced shear failure is established. The cavitation-induced shear failure process of the plugging layer is systematically studied with the aid of granular material mechanics and liquid bridge theory. In addition, laboratory experiments of reversed pressure-bearing were carried out based on the principle of reversed cavitation. Results show that the cavitation-induced shear failure of the fractured sealing layer is a special kind of failure modes of the plugging layerin gas reservoirs. This process can be divided into three steps: viscosity reduction because of gas diffusion, cavitation-induced shear stripping and fluids displacement mismatch shearing destructions. In addition, the experimental results show that the plugging layer with a positive pressure of 6 MPa has different shear failure resistances for different fluids. With the displacement medium changing from liquid to gas, the reversed pressure-bearing value of the plugging layer decreases from 2.0 MPa (22 min) and 2.5 MPa (30 min) to 1.5 MPa (10 min) and 1.0 MPa (12 min), respectively. The comprehensive shear resistance is reduced by approximately 50%, indicating that gas has different destructive ability and destructive mechanism compared to liquid.