An experimental investigation of dynamic elastic moduli and acoustic velocities in heterogeneous carbonate oil reservoirs

One of the most common methods for determining elastic moduli of rocks is the acoustic velocity log. The elastic moduli of reservoir rocks are widely used in geomechanical modeling, borehole stability analysis, and hydraulic fracture design. In the carbonate reservoirs, the effect of the fluid type on the dynamic elastic modulus under high pressure conditions have rarely been investigated. Carbonate oil reservoirs are known for their heterogeneity and anisotropic nature. Therefore, it is a challenge to find a reliable correlation between the acoustic velocity and rock/fluid properties. In this paper, the acoustic velocities of several carbonate samples with a wide range of porosity and permeability from different oil reservoirs were measured under different confining and axial stresses. Our study shows that wettability of rock samples plays an important role in the acoustic velocities, particularly in tight pores. In addition, an increase in compressional velocity after saturation was reported. In order to fully understand the effect of fluid type, a new parameter [relative change of shear modulus (RCS)] is defined. Experimental results shows that strong water wet samples have higher RCS values rather than oil wet samples which means that the wettability of the carbonate rocks is one of the main important factors in dynamic elastic modulus.