不同压力下部分饱和砂岩纵波衰减的理论及实验研究

深入了解不同压力、频率、流体含量和流体分布对岩石中弹性波传播特性的影响,对指导油气勘探开发具有重要意义.不同尺度下的波致流效应,是声波传播过程中产生速度频散和衰减的重要原因.本文以不同压力下水饱和区域改进的骨架模量为纽带,建立了联合介观尺度斑块饱和效应与微观尺度喷射流效应的部分饱和岩石声学理论模型.开展针对性声学实验,根据不同压力下部分饱和砂岩纵波速度测量数据,确定理论模型中的相关参数,从而实现对不同压力下部分饱和岩石纵波衰减的定量表征.在此基础上,通过理论与实验测量的纵波衰减的对比,分析不同压力、含水饱和度以及频率对岩石纵波衰减的影响.研究结果表明,在较低压力,较高含水饱和度以及较高频段,喷射流效应较强,因此新建模型计算的衰减明显大于斑块饱和模型的衰减.由于新建模型体现了斑块饱和效应与喷射流效应的综合影响,相比于斑块饱和模型,新建模型计算的部分饱和岩石的纵波衰减更接近于实测衰减,但受到岩石自身因素影响,新建模型计算的衰减仍略小于实测衰减.

Theoretical and experimental study of P-wave attenuation in partially saturated sandstones under different pressures

Understanding the effects of pressures,frequencies,fluid content,and fluid distributions on the elastic wave propagation in reservoir rocks is of great importance in guiding oil and gas exploration. Wave-induced fluid flow at different scales is a major cause of the velocity dispersion and attenuation during the propagation of elastic waves. In this work,a new model of partially saturated rock was proposed by combining patchy saturation effects in mesoscale and squirt flow effects in microscale,based on the modified frame modulus of water saturated regions under pressures. On the other hand,we measured the P-wave velocity and attenuation of partially saturated sandstones with varying pressures. After calibrating the unknown parameters in the proposed model using the measured velocity,the model can be employed to quantitatively characterize the P-wave attenuation. The influence of pressures,water saturation and frequencies on the P-wave attenuation in rocks was further analyzed by the comparison between the modeled attenuation and the measured values. The results show that the squirt flow effects made the attenuation calculated by the new model significantly larger than that calculated by the patchy saturation model at low pressures,high water saturation and high frequency bands. Because it combines both patchy saturation and squirt flow effects,the P-wave attenuation of partially saturated rocks calculated by the new model is closer to the measured attenuatio compared with the patchy saturation model,although the modeled attenuation still slightly underestimates the measured attenuation.