不同围压和流体饱和状态下致密砂岩弹性各向异性特征

为研究致密砂岩声波速度及其各向异性随围压的变化规律以及不同流体饱和状态下的弹性各向异性特征,钻取了不同方向的岩心并在实验室超声波频率下对致密砂岩的声学特性进行了测量,分别给出干燥和饱和水状态下,不同方向样品纵横波速度、刚性系数以及各向异性系数随围压的变化规律,并对实验结果进行了分析讨论.实验结果表明致密砂岩纵横波速度、纵横波速度比以及刚性系数均随围压增加而增加,但其在不同饱和状态下的变化率却截然不同;纵横波速度比、各向异性系数在饱和水状态下变化规律不明显,表明孔隙流体的存在对于岩石物理性质有着非常重要的影响.这方面的实验工作不但对于考察不同流体性质对致密岩石弹性各向异性影响是必要的,而且有助于致密砂岩油水和气层的识别.

Elastic anisotropy characteristics of tight sands under different confining pressures and fluid saturation states

With continued growth in world demand for oil and gas and declined production for conventional oil and gas, unconventional oil and gas with large resource potential has gradually become a new field of exploration. The tight oil becomes one of the highlights of global unconventional petroleum exploration and development.#br#Porosity and permeability of tight sandstone are very low. There is no natural production capacity or natural production capacity is very low in the general conditions. So, large-scale fracturing is needed to produce industrial oil and gas flow. However, experience has shown that the production of tight sandstones of different fracturing section and different perforation clusters is not the same due to lithology and stress factors caused by the heterogeneity even if the large scale fracturing is used. Therefore, it is important to investigate the anisotropic properties of tight sandstone.#br#To investigate the laws of tight sandstone wave velocity and anisotropy with confining pressure and elastic anisotropy characteristics under different saturated states, cores in different directions were drilled and their acoustic characteristics were measured under ultrasonic frequency in laboratory. Change laws of sample P and S wave velocity, stiffness coefficient, and anisotropy coefficient with increasing confining pressure were then analyzed. The experimental results indicate that P and S wave velocity, ratio of P wave to S wave and stiffness coefficient all raise with increasing confining pressure, but the change rates under different saturated status were entirely different. Ratio of P wave to S wave and anisotropy coefficients have inconspicuous change law under saturation state, this indicates that the existence of fluid is very important to rock physical properties. The experimental work is not only necessary to investigate tight sand elastic anisotropy characteristic under different fluid properties, but also contribute to identification of tight sandstone fluid and gas.