Study On Rock Acoustic Properties Of Low Porosity And Low Permeability Sandstone Reservoir

With the further extension of oil exploration and development, most high porosity and high permeability reservoirs have been developed in China. The exploration targets gradually turned to low porosity and low permeability reservoirs. The difficulties of exploration increased. Seismic exploration is applied in oilfield exploration widely. Due to the wide applied range, seismic exploration results are not that accurate. With the increase of the difficulty of exploration, the seismic exploration data needs higher precision and requirement in the application of low porosity and low permeability reservoir, which requires other exploration methods and auxiliary of rock physical research. The theory of rock physics is the foundation of the oilfield exploration.Rock physical studies can make us know the information of underground formation well. Then the underground fluid and formation can be recognized accurately. The conventional rock physics theory does not fit the low porosity and low permeability reservoir well and predict the reservoir effectively because of the complex reservoir structure. The conventional rock physics model need to be improved to serve the seismic work accurately.Based on the rock acoustic theory,the experiments of low porosity and low permeability sandstone samples in S area have been done in this paper. Biot coefficient has been calculated and the fitting formula between Biot coefficient and has been established based on the experimental data. Then the extensional Gassmann equation was obtained. For the low porosity and low permeability reservoir, the disconnected porosity should be considered, which influenced the elasticity modulus of matrix mineral.The extensional Gassmann equation considered the disconnected porosity has been established for the low porosity and low permeability reservoir. The experimental data have been used to obtain some acoustic velocity empirical formula for low porosity and low permeability reservoir.The result show that:1) The extensional Gassmann equation based on the rock physical experiment data can be used for fluid replacement that the advantage is omit the calculation of dry rock modulus. 2) For low porosity and low permeabilityreservoirs, the extensional Gassmann equation that considered disconnected porosity is more in line with the actual situation and has stronger applicability. 3) For low porosity and low permeability reservoirs, the actual reservoir rock sample should be used to get p-wave and s-wave velocity empirical formulae and other factors should be considered to get accurate results.