Evaluation Of The Effect Of Eor Processes On Seismic Wave Velocities

Abstract The capability to monitor the enhanced oil recovery processes in heavy oil reservoirs by active or passive seismic methods provides valuable tools for the reservoir engineer to manage the recovery process. The seismic wave velocities (compressional and shear wave) in reservoir formations are strongly dependent on the formation's mechanical and thermal characteristics which are influenced by changes in temperature, pore pressure and stress slate. In order to analyze and understand lhe field seismic data, the influence of temperature, pore pressure and compressional and shear deformations on the seismic wave velocities must be known. A state-of-the-art laboratory testing system to determine these influences on seismic wave velocities has been developed and is described in this paper. The calibration oi the equipment and typical calibration results determined during the development of the apparatus are presented. Introduction Enhanced oil recovery (EOR) processes are used to extract bitumen and heavy oil from deeply buried heavy oil reservoirs by water or steam flooding, cyclic steam stimulation or fire flooding. The capability to monitor EOR processes by active or passive seismic methods provides new tools for the reservoir engineer to monitor the recovery development. Such monitoring allows the reservoir engineer to know when the recovery process should be altered and to modify the processes promptly. The strong dependence of seismic wave velocities in oil sand and heavy oil reservoir formations on the formation's mechanical and thermal characteristics make it possible to apply in situ seismic methods to track the progress of temperature fronts, flooded zones and fractures; and to assess the effectiveness of the thermally enhanced oil recovery processes. However, to allow these seismic monitoring methods to be used in situ, the influence of temperature, pore pressure, effective stress, compressional and shear deformations on the seismic wave velocities must be known. A comprehensive laboratory study is underway at the University of Alberta in geomechanics engineering to identify the effects of temperature, pore pressure, effective stress, porosity, volumetric changes, shearing, gas and liquid saturation on the seismic velocities. This research will provided important data to assist in the interpretation of field seismic survey results. The objective of this paper is to describe the development of laboratory equipment for the measurement of seismic velocities under controlled conditions of confining stress, shear stress and temperature. The calibration of the equipment and typical calibration results determined during the development of the apparatus are presented. Material Changes Affecting Seismic Wave Velocities Research by Tosaya et al. (1988); Wang (1989); Wang and Nur (1987, 1988, 1989, 1990) show that seismic wave velocities in oil sand and heavy oil bearing materials decrease significantly as the temperature increases. Other research by Agar (1984); Agar, Morgenstern and Scott (1989); Kosar (1989); Scott, Adhikary and Proskin (1991) show that during the recovery processes, stresses and deformations occur in the reservoir and adjacent strata which are caused by changes in pore pressures and temperature. These changes cause shearing and compressive deformations which can affect formation permeability and hydraulic fracturing.