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对不同饱和状况下的孔隙岩层中的地震纵波和横波的速度已经从理论上作了计算,并与实验室资料作了比较。从理论上说,岩石可用固体基质、球状孔隙和扁椭球体状的孔隙来表示。在计算受额定压力影响的速度时,考虑了孔隙的密集程度和饱和压缩系数。如果其他参数固定不变,理论上的计算表明,在相同浓度中,扁孔隙(小纵横比)比成圆形的孔隙对弹性模量和速度的影响更大。饱和流体(气、油或水)的性质对压缩速度的影响比对切变速度的影响大。纵波速度在水饱和岩中比在干岩石或气饱和岩石中高。通常,横波的性质正好相反,切变速度在干岩石或气饱和岩石中则比在水饱和岩石中高。在实验室里,作为压力的函数测定的干的和水饱和的花岗岩、石灰岩、砂岩样品的切变速度与理论曲线相拟合,并计算了与资料相拟合的孔隙形状谱。要求从球状到相当细微的裂缝(纵横比为1至10~5)的孔隙形状的谱与资料相拟合。用这些模型计算的理论速度与在水饱和岩石、冻结的岩石中测得的速度以及局部饱和岩石中的纵波速度相拟合。在实验室资料基础上得来的岩石样品,对不同压力和温度下的气、油和卤水的完全或局部饱和储集层的理论地震速度作了计算。卤水饱和中的压缩速度最高,而气饱和中的压缩速度最低。随压力增大差异减小。当卤水中存在少量(5％)气体,成为不相容的混合物时,压缩速度显著下降,在某些压力下甚至低于完全气饱和中的数值。砂岩模型中,在对应于浅层和适当深度(约8000呎以内)的压力上,气——卤水界面纵波的反射系数是高的。当额定压力更大时,除了非常高的孔隙流体压力(气体压力)外,其反射系数变小。因此,深层的强反射或“亮点”可能表示过压层位。由于混合气体——卤水界面的反射系数低于纯气界面的反射系数。根据层速度和反射振幅可能有助于分辨混合气体——卤水储集。气饱和岩石的泊松比低于卤水饱和岩石。在较深的深层中,这些差异仍然存在。
The velocities of seismic longitudinal and shear waves in the pore rock under different saturation conditions have been calculated theoretically and compared with the laboratory data. In theory, rocks can be represented by solid matrices, spherical pores and oblate ellipsoidal pores. In calculating the velocity affected by the rated pressure, the density of the pores and the coefficient of saturated compressibility are taken into account. If the other parameters are constant, theoretical calculations show that at the same concentration, the flat pores (small aspect ratio) have a greater effect on elastic modulus and velocity than circular pores. The effect of the properties of a saturated fluid (gas, oil or water) on the compression rate is greater than on the shear rate. P-wave velocity is higher in water-saturated rocks than in dry or gas-saturated rocks. In general, shear waves are the opposite in nature, with shear rates higher in dry or gas-saturated rocks than in water-saturated rocks. In the laboratory, shear rates of dry and water saturated granite, limestone and sandstone samples measured as a function of pressure were fitted to the theoretical curves and the pore shape spectra fitted to the data were calculated. It is required that the spectrum of the shape of the pores from the spherical shape to the very fine cracks (aspect ratio of 1 to 10 to 5) be fitted with the data. The theoretical velocities calculated with these models fit the velocities measured in water-saturated rock, frozen rock, and the longitudinal wave velocity in locally saturated rocks. Rock samples based on laboratory data are calculated for theoretical seismic velocities of fully or partially saturated reservoirs of gas, oil and brine at different pressures and temperatures. Brine saturation is highest in compression and lowest in gas saturation. As pressure increases, the difference decreases. When a small amount (5%) of gas is present in the brine and becomes an incompatible mixture, the compression rate drops significantly, at some pressures even below full gas saturation. In sandstone models, the reflection coefficient of longitudinal waves at the gas-brine interface is high at pressures corresponding to shallow and appropriate depths (within about 8000 feet). When the rated pressure is larger, the reflection coefficient becomes smaller except for very high pore fluid pressure (gas pressure). Therefore, deep strong reflections or “bright spots” may indicate overpressure levels. Since the gas-brine interface has a lower reflection coefficient than the pure gas interface. Depending on the velocity of the layer and the amplitude of the reflection it may be helpful to distinguish the gas-brine reservoir. The Poisson’s ratio of gas-saturated rocks is lower than that of brine-saturated rocks. In the deeper, these differences still exist.