碳酸盐岩储层流体替换中混相流体体积模量的计算

流体替换是研究流体对储层岩石物理参数影响的重要手段。在流体替换过程中,通常使用Woods方程计算混相流体的体积模量,但对于碳酸盐岩储层,由于其基质孔隙度低,岩石内存在不均匀充填的情况,Woods方程不再适用,为此,对斑块充填(Patchy)条件下混相流体体积模量的计算方法进行了更为深入的研究。通过对Patchy模型极端情形的研究,得到了饱和斑块充填情况下混相流体的计算模型。混相流体均匀充填和饱和斑块充填模型分别对应于混相流体充填的两种极端情况,所计算的结果分别是实际混相流体体积模量的上限和下限。考虑实际储层中混相流体的复杂充填状态,将利用Woods方程和Patchy模型计算的流体体积模量取算术平均(VRH模型),所得结果作为近似的混相流体体积模量。南方某探区碳酸盐岩储层实际流体替换结果表明,利用Woods方程和Patchy模型计算的结果有明显差异,利用VRH模型计算的结果是较为可信的。

Calculation of bulk modulus for mixed-phase fluid in fluid substitution for carbonate reservoir

Fluid substitution is one of the important means for analyzing the impact of fluid on reservoir rock physical parameters.During fluid substitution,Wood’s equation is widely used to determine bulk modulus of mixed-phase fluid.But for carbonate reservoirs,because of the low porosity of the matrix,heterogeneous filling exists in rocks,so Wood’s equation is not suitable any more.Instead,Patchy saturation model can be applied under this situation.Through the study of an extreme case of Patchy saturation model,an equation for calculating bulk modulus of the mixed-phase fluid filled with patchy saturation is given.Homogenous filled(Wood’s equation) and fully patchy saturation model are two extreme cases of fluid saturation,and the corresponding equations for the two model corresponding to the upper and lower limit of the bulk modulus of mixed-phase fluid.Taking the complexity of saturation in the real case into account,average of the two equations(such as VRH model) is used to calculate bulk modulus of the mixed-phase fluid.Actual fluid substitution results for the carbonate reservoir in Southern exploration area is different by using Wood’s equation and Patchy model,and the result by using VRH model is reliable.