Anisotropic rock physics modeling of tight sandstone and applications

Key words:  tight reservoir  rock physics  anisotropy  fracture density

Abstract:

One distinguishing feature of low-porosity and low-permeability sandstones is the departure of their elastic properties from general porous and permeable sands. This paper developed a rock physics model focusing on the developed cracks in tight sandstones and their effects on tight sand. Pores with fluids were added to the rock matrix by using effective media theory, and cracks with fluids were added by using anisotropic fluid substitution equations which were derived by combining Hudson model and anisotropic Gassmann 's equations. The elastic modulus in tight sandstones were then calculated with different crack properties, such as crack density, crack shape, fluid content, and so on. The accuracy of the parameters estimation method was discussed based on rock physics model considering micro cracks. P-wave and S-wave velocities were estimated with the proposed modeling method. The accuracy and advantage of the model are verified by comparing with the real logging data. Thomsen parameters of fracture reservoir are extracted and can be used to indicate the cracks in reservoirs.