Читать книгу Reservoir Characterization - Группа авторов - Страница 32

Haleh Azizia1*, Hamid Reza Siahkoohi2, Brian Evans3, Nasser Keshavarz Farajkhah4 and Ezatollah KazemZadeh4

1Department of Geophysics, Science and Research Branch, Islamic Azad University, Tehran, Iran

2Institute of Geophysics, University of Tehran, Tehran, Iran

3Department of Petroleum Engineering, Curtin University, Perth, Australia

4Research Institute of Petroleum Industry, Tehran, Iran

Abstract

The objective of this study is to assess the accuracy of the empiricalequations in estimating the shear wave velocity and elastic modulus of rock sample at reservoir pressure condition. The evaluated relations are Gassman, Greenberg and Castagna which have been in use by researchers for a long time and have shown acceptable results. The plug sample investigated in this study is taken from Berea sandstone reservoir southwest of Australia, which is a known reference sandstone for this type of study. This plug in the laboratory was flooded with supercritical carbon dioxide fluid, saturated and pressured under axial, radial and pore pressure comparable to oil reservoirs pressures, after which elastic wave velocity and elasticity modules were determined. Then, using empirical relationships such as Gassman, Greenberg and Castagna and measured values of P-wave velocity, shear wave velocity, and elasticity coefficients were estimated. Comparison of theoretical values versus experimental values shows they compare very well, only in some cases a difference between estimated and experimental values for the coefficients of elasticity has been observed. We believe that the difference is due to the assumptions that were made in those theories. The shear wave modulus didn’t remain constant during fluid saturation. Also, the measured bulk modulus and the calculated values based on Gassman formula did not compare very well. This difference was observed to be larger at higher pressures.

Keywords: Wave velocity estimate, elastic waves, the coefficients of elasticity, rock physics, reservoir conditions, Gassman relations, Greenberg – Castagna theory, injecting carbon dioxide, sandstone