A Case Study of a Fine Scale Integrated Geological, Geophysical, Petrophysical, and Reservoir Simulation Reservoir Characterization With Uncertainty Estimation

A novel method for the integration of multi-scale rock and fluid information was performed on a single well deep-water exploration discovery. The method integrates diverse data types through physically constrained models into a single earth model. Development scenarios were optimized through multiple flow simulations. The development scenarios were designed to investigate the range of uncertainty in the earth model. This technique utilizes a single integrated earth model and multiple simulations in contrast to techniques that cannot reproduce the seismic, or reproduce the seismic but require a flow simulation for each geologic “realization”. The pending business decisions required reservoir characterization with the greatest precision possible and an understanding of the inherent uncertainties. The discovery was made based on 3-D seismic amplitudes, but a portion of the potential reservoir appeared to be obscured by a shallower seismic event. The available borehole data with which to construct the earth model consisted of conventional wireline logs and a wireline-conveyed formation tester from a single penetration. No flow tests, core or fluid samples were available. The technique honors all the observed data through the alteration of an initial geologic model until, through upscaling, an acceptable match is made with acoustic impedance determined from the observed seismic. The link between the geology and seismic is a rock physics model consistent with the well data. The rock physics model is used to estimate the equivalent seismic properties from the porosity and fluid saturations in the fine scale geologic model. The objective is to minimize the difference between acoustic impedance generated from the 3-D seismic data and the forward-modeled very-fine scale geologic model. The uncertainties associated with each measurement and derived variables were assessed at each step. The resulting model will reproduce the original seismic amplitude data and all of the well data, although the well data were not explicitly used in the seismic inversion or the “inversion-of-the-inversion” estimation of petrophysical properties. Each cell in the resulting fine-scale geologic model contains porosity, permeability, and oil saturation. The static model was up-scaled for dynamic flow simulation to estimate productivity and evaluate various development schemes. Numerous simulations were performed to address uncertainties in the geologic model and to account for risks associated with the geophysical imaging problems, and flow capacity. Two sets of distributions were assigned to porosity and permeability in the simulator for separate areas of the reservoir. A distribution was also assigned to fault transmissibility. The results of hundreds of simulator realizations were then used to estimate the range of uncertainty in reservoir performance under varied development scenarios. Introduction An accurate and precise prediction of reservoir rock and fluid properties is fundamental to the prediction of reservoir performance. Improved results are obtained when all of the available data are integrated. However, there are significant scale and measurement issues in the integration of all data types. As an example, a porosity interpretation from wireline logs in a well bore usually samples on the order of 13 cubic feet, or 0.1% of the volume of a 328 by 328 by 1⁄2 foot cell. A core plug would sample only 0.0001% of the volume. Fortunately, seismic samples 100% of the sub-surface and is therefore a critical measurement for inter-well property description. Seismic responds to impedance changes in the subsurface, but does not directly measure reservoir properties such as porosity, fluid saturation, permeability. To fully incorporate seismic information into reservoir characterization, a technique was developed to assure consistency between geology, rock and fluid properties, and acoustic impedance from seismic. Dynamic probabilistic reservoir simulation uses the reservoir property model and the associated uncertainties as input. The workflow to implement the technique consisted of both well-known and novel components. The traditional steps were: borehole petrophysical evaluation, development of a rock physics model from wireline log measurements, stratigraphically-constrained seismic inversion, construction of a 3-D geocellular model, conversion of the time-based SPE 84274 A Case Study of a Fine Scale Integrated Geological, Geophysical, Petrophysical, and Reservoir Simulation Reservoir Characterization With Uncertainty Estimation J.G. Hamman SPE, R.E. Buettner SPE, D.H. Caldwell SPE, Marathon Oil Co.