流体饱和储层砂岩超声波纵波速度频散的定量预测

针对岩芯的实验室超声波测试速度由于频散误差而不能直接用于涠西南凹陷声波测井速度标定的问题,利用涠三段5块不同物性的储层砂岩,通过比较盐水和4种不同密度油作为孔隙流体时的饱和岩样超声波纵波速度变化,优化和完善速度频散机制分析流程,提出和验证样品被喷射流机制统治时的非弛豫湿骨架模量与高压情况下的干骨架模量相当的假设,并探索出一种BISQ理论特征喷射流长度(R)的估计方法。最后建立对涠三段储层砂岩的纵波速度频散进行全频带定量预测的方法,从而能够确定速度频散的机制和大小。通过提出的全频带速度频散预测公式,可将实验室的超声波测试速度校正到不同频率条件,在实际应用中满足测井(中频带)和勘探地震(低频带)的岩石物理分析需求,具有一定实践意义。

The Quantitative Prediction of Ultrasonic Compressive Wave Velocity Dispersion for Fluid Saturated Reservoir Sandstone

Due to the velocity dispersion error, the laboratory ultrasonic velocity measurement of core samples cannot be directly used to calibrate the acoustic well logging velocity of reservoir in Southwest Weizhou depression. The further work of data processing and analysis for the ultrasonic velocity dispersion were conducted for 5 representative sandstone samples of W3 reservoir. By comparing the compressive velocities of sandstone samples saturated with the brine and four oils of different densities, the method and process of velocity dispersion mechanism analysis were greatly improved. The assumption was proposed and verified that the modulus of non-relaxation wet solid frame was equivalent with the one of dry frame under high pressure condition when the sandstone samples were ruled by squirt flow mechanism. The estimation method ofR value, which was the critical squirt length of BISQ theory, was also proposed and verified. Then, the method to quantitatively predict the P-wave velocity dispersion of W3 reservoir sandstones in full waveband was accomplished. Finally it is concluded that the mechanism and degree of velocity dispersion depend on both the physical properties (porosity and permeability) of samples and the kinematic viscosity of pore fluids. Using the velocity dispersion prediction formula for full waveband, the ultrasonic velocity measured in laboratory (high frequency band) can be corrected to different frequency, and then meet the demands of rock physics analysis for well logging (medium frequency band) and exploration seismology (low frequency band). Thus, the complete technique for velocity dispersion analysis and prediction has certain practical meaning.