Integrated Reservoir Characterization of a Complex Carbonate Field

Abstract

Abstract Multidisciplinary teams of geologists, geophysicists, and petroleum engineers create unique working environments as each member brings his own different perspective to the team. These different viewpoints make integrated teams effective in solving reservoir management problems. A full understanding of the spatial distribution and interdependency of reservoir properties such as porosity, water saturation, permeability, formation volume factors, and rock properties is essential for reservoir management plans to be effective. The integrated team working on Joffre field, Alberta has successfully brought together the available data from the three disciplines to form a comprehensive understanding of the reservoir. The Reservoir Characterization Project (RCP) at the Colorado School of Mines conducts research into the application of 3-D, 3-C (multicomponent) reflection seismology for improved reservoir description and exploitation. The current research is oriented towards using shear waves to characterize reservoirs where compressional seismic data have not been effective. In the Joffre field the compressional seismic data has been ineffective in discerning porous and non-porous reservoir development. A 3-D multicomponent (3-D, 3-C) seismic survey was collected over the northeastern limit of Joffre field, Alberta by RCP. Application of this new technology towards reservoir description is a key element of this multidisciplinary study. The focus of this research and survey is lithology and porosity discrimination within the upper Devonian, Nisku dolomite reservoir. Detailed geologic studies of cores from this reservoir revealed depositional and diagenetic heterogeneities, which influence production. A stromatoporoid/coral boundstone reef facies within the lower Nisku reservoir section exhibits thickness variations in northeasterly oriented elongate patterns that parallel both the basin paleostrike and the underlying Bashaw Complex edge. These features have influenced the overlying succession of Nisku reservoir rocks and rock properties. Velocity ratio (Vp/Vs) mapping of 3-D, 3-C seismic data is a powerful porosity discrimination tool. Higher Vp/Vs ratios found over the productive Nisku reservoir correlate with thick high porosity zones. The 3-D shear wave data also show spatial correlation of the Si (fast) shear wave amplitudes with porosity. By incorporating results from this new seismic technology with detailed vertical mapping of reservoir geology and rock properties into a simulation model, improved exploitation can be achieved. Horizontal drilling has been initiated in the field, confirming the reservoir model. The incorporation of the more detailed information with respect to changes in rock properties and the specific locations of low permeability zones that have significantly restricted pressure communication and impacted fluid flow patterns have aided in the evaluation of field performance. Effective management decisions can now be made to redirect the field development in order to enhance oil recovery. Being able to establish where the unswept or unaffected areas of the reservoir are will allow for infill drilling and redesign of the waterflood pattern. Introduction Joffre field is located in south-central Alberta, near the city of Red Deer on the inner Nisku shelf. The Nisku Formation (D2) at Joffre is a dolomitic shelf carbonate of upper Devonian (Frasnian) age. This reservoir was discovered in 1956 and has produced approximately 7 million cubic meters (43 MMSTB) of oil, which is estimated to be 35% of the recoverable reserves. updip and lateral filling of porosity with anhydrite has produced the hydrocarbon trapping mechanism. This 20 to 25 meter (66 to 82 ft.) thick reservoir has highly variable porosity. The geologic complexity of this reservoir, its production spacing units and the hydrocarbon production history suggest that significant additional reserves remain to be recovered. Other Nisku reservoirs in this region have successfully achieved 45% recovery of reserves. The challenge at Joffre is to understand why field performance is different. Compressional seismic data have failed to delineate the Joffre Nisku pool. The northeastern edge of the field was selected for a 3-D, 3-C seismic survey where the Nisku reservoir is present in both updip and lateral sealing positions, and where widely spaced well control (160 ac.) defines this reservoir edge (Figure 1). P. 915