Laboratory study of fluid viscosity induced ultrasonic velocity dispersion in reservoir sandstones
Laboratory study of fluid viscosity induced ultrasonic velocity dispersion in reservoir sandstones
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DOI：
10.1007/s11770-010-0235-3
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发表时间：
2010-07
影响因子：
0.7
通讯作者：
T. He;C. Zou;Fa-Gen Pei;Ke-Ying Ren;Fan-Da Kong;G. Shi
中科院分区：
文献类型：
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作者：
T. He;C. Zou;Fa-Gen Pei;Ke-Ying Ren;Fan-Da Kong;G. Shi
在实验室模拟现场压力条件下，测量了饱和砂岩样品的超声波声速。这些样品取自WXS凹陷的W地层，涵盖了低至接近高的孔隙度和渗透率范围。以盐水和四种不同密度的原油作为孔隙流体，研究了流体粘度引起的速度频散。通过对实验观测资料的分析表明：（1）毕奥模型可以解释大部分微小的速度离散现象对于被本实验中所用的所有流体饱和的高孔隙度和渗透率样品，超声波测量与零频率Gassmann预测之间的差异约为2-3%，并且对于被低粘度流体饱和的中等孔隙度和渗透率样品也是有效的（小于约3 mP·S）和（2）当流体粘度增加时，喷射流动机制主导低至中等孔隙度和渗透率样品，并产生高达约8%的大的速度分散。对储层砂岩的微裂缝纵横比也进行了估算，并将其应用于计算喷流模型的特征频率，在此基础上违背了Gassmann的假设，测得的高频速度不能直接用于W组砂岩勘探地震频带的Gassmann流体置换。
Ultrasonic velocities of a set of saturated sandstone samples were measured at simulated in-situ pressures in the laboratory. The samples were obtained from the W formation of the WXS Depression and covered low to nearly high porosity and permeability ranges. The brine and four different density oils were used as pore fluids, which provided a good chance to investigate fluid viscosity-induced velocity dispersion. The analysis of experimental observations of velocity dispersion indicates that (1) the Biot model can explain most of the small discrepancy (about 2–3%) between ultrasonic measurements and zero frequency Gassmann predictions for high porosity and permeability samples saturated by all the fluids used in this experiment and is also valid for medium porosity and permeability samples saturated with low viscosity fluids (less than approximately 3 mP·S) and (2) the squirt flow mechanism dominates the low to medium porosity and permeability samples when fluid viscosity increases and produces large velocity dispersions as high as about 8%. The microfracture aspect ratios were also estimated for the reservoir sandstones and applied to calculate the characteristic frequency of the squirt flow model, above which the Gassmann’ s assumptions are violated and the measured high frequency velocities cannot be directly used for Gassmann’s fluid replacement at the exploration seismic frequency band for W formation sandstones.