含不同孔隙流体的砂岩地震波速度随压力变化的实验研究

岩石的地震波性质是区域构造研究和浅部地震勘探应用的基础.延长油田是我国重要的油气生产基地之一,但目前仍缺乏地震波性质方面的基础资料.作者利用Autolab2000多功能岩石物性自动测试设备,在0~180MPa及饱含不同孔隙流体(干燥、饱水及饱油)条件下,研究了三种来自延长油田砂岩岩芯的纵波、横波速度.结果表明:三种砂岩的V_p、V_s1和V_s2均随压力增加(或降低)而基本呈对数曲线增大(或减小);干燥、饱水和饱油三种波速间的关系因砂岩类型不同而不同,这主要取决于岩石的有效弹性模量、孔隙流体性质以及岩石的内部结构等;含同种孔隙流体的不同类型砂岩,其V_p、V_s1和V_s2随压力变化的规律主要受岩石孔隙度和粒度的影响;而含不同孔隙流体的同种砂岩,其V_p、V_s1和V_s2随压力变化的规律则主要受控于岩石的有效弹性模量和流体密度.另外,含水或含油饱和度的变化对V_s1和V_s2基本没有影响.实验结果可以为该地区地震资料的解释及与声波测井之间的对比提供重要的基础数据和参考依据.

A laboratory study of seismic wave velocity in sandstone bearing differential pore fluids at different pressures

Seismic properties of rock have a wide range of applications in regional tectonic research and shallow seismic exploration. The Yanchang oilfield is one of the important production bases for oil and gas in China, but there is no data of seismic wave. This paper applied the AutoLab 2000 computer-controlled servo hydraulic triaxial test system to obtain accurate P- and S-wave velocity data at pressures up to 180MPa on three kinds of core samples of sandstone in dry, water and oil-saturated conditions from the Yanchang oilfield. The results show the wave velocities V_p, V_s1 and V_s2 for the three kinds of samples of sandstone change basically logarithmically with increasing or decreasing pressure; the relationship between wave velocities in dry, water and oil saturated conditios indicates obvious differences for three kinds of core samples of sandstone, mainly because rock elastic modulus, pore fluid property, and rock structure are different. For the different kinds of sandstone, the pressure dependence of the V_p, V_s1 and V_s2 in the same pore fluid is controlled by the porosity and grain size, and for the same kind of sandstone, the pressure dependence of the V_p,V_s1 and V_s2 in the different pore fluids is affected by the effective modulus of elasticity and density. Moreover, V_s1 and V_s2 hardly vary with water and oil saturation. The experimental results can provide an important basis for the interpretation of seismic data and comparison with well log data in that region.