含微裂缝致密砂岩核磁共振响应机理研究

微裂缝是致密砂岩储层中流体的重要储存空间和迁移通道，为充分了解含微裂缝致密砂岩的核磁共振响应机理，构建了含不同微裂缝的致密砂岩数字岩心，并采用随机游走法对其在饱和油水时的核磁共振（NMR）响应进行了模拟。模拟结果表明:微裂缝的张开度、长度以及裂缝内含水饱和度为影响储层流体NMR响应的主要因素，张开度、长度以及含水饱和度的增加均会使水峰弛豫时间与信号幅度增大，但当微裂缝长度超过100 μm后，水峰弛豫时间不受上述因素影响；油峰弛豫时间不受微裂缝张开度、长度以及裂缝内含水饱和度的影响，其信号幅度反映含油量；微裂缝倾斜角对NMR响应没有影响。研究结果揭示了含微裂缝致密砂岩储层的NMR响应机理，为勘探微裂缝发育的有利层段提供了理论依据。 

Study on the NMR Response Mechanism of Micro-Fractured Tight Sandstones

Micro fractures serve as important storage spaces and migration channels for fluids in tight sandstone reservoirs. In order to fully understand the NMR (nuclear magnetic resonance) response mechanism of micro-fractured tight sandstones, we constructed several digital cores of tight sandstones with different micro fractures and simulated their NMR responses under oil-water saturation conditions by employing the random walk method. The simulation results showed that the aperture and length of micro fractures as well as the water saturation in fractures were the main controlling factors in the NMR response of reservoir fluids. In addition, the increase in the aperture, length, and water saturation could result in an improvement in relaxation time and signal amplitude of the water peak. However, the relaxation time of the water peak was not affected by above factors for micro fractures with length over 100 μm. Furthermore, the relaxation time of oil peak was independent of aperture, length, and water saturation, oil content was reflected from signal amplitude, and the inclination angle of micro fractures exerted no impact on the NMR response. The research results revealed the NMR response mechanism of micro-fractured tight sandstone reservoirs and provided a theoretical basis for the identification of favorable sections with micro-fracture developed.