Abstract: Integrated Carbonate Reservoir Characterization and Modeling Using Outcrop, Subsurface and Seismic Data and Technologies: An Example from the Permian Basin, U.S.A.

Fitchen, W. M., Drexler, C. W., Frantes, T. J., Helwick, S. J., Kozar, M. G., Mitchell, J. C., Rankey, E. C., and Schroeder, F. W. - Exxon Production Research Company

A fundamental challenge in characterizing carbonate reservoir properties and undertaking 3-D geologic modeling of facies and porosity is the prediction of property continuity and associated uncertainty away from the wellbore. ?Successful? prediction, i.e., accurate prediction of pore volume within the reservoir, depends on (1) data availability (type, spacing, quality and resolution), (2) the quality of the structural, sequence stratigraphic, and facies frameworks, which requires appropriate models and concepts as well as innovative model-building procedures, (3) the degree to which different data types are integrated and interpretations are cross-checked for consistency, and (4) the modeling techniques used to predict property continuity while incorporating and/or subsequently quantifying uncertainty. The different stages of exploration, field appraisal, development, and enhanced recovery witness changes in data, time and cost budgets, and objectives (e.g., assessment, flow simulation, production optimization); these factors exert a major influence on the scope of the reservoir characterization and model construction and thus also influence the relative success of property prediction. In this study, we quantify the value of integrating outcrop analogs and 3D seismic data - two data types that provide measures of property continuity - into the reservoir characterization and 3D geologic model construction process.

The oil field studied, complemented by nearby world-class outcrop analogs in the Guadalupe Mountains, provides an exceptional proprietary database to examine the role of outcrop analogs and 3D seismic data in reservoir characterization and 3D geologic model construction. The producing formation in the field, the San Andres Formation (Middle Permian), is a heterogeneous restricted platform carbonate reservoir with over 950 wells on 10 to 20 acre spacing; a recent full-field, high effort 3-D seismic survey; over 13,000 ft of calibrated core data; oil, water and CO₂ production and injection data; and a suite of engineering test data (injection profiles, production surveys, buildup tests).

Outcrop analogs and seismic attributes provide critical data to appraisal and development stage descriptive and modeling efforts. Outcrop analogs were used to develop regional to flow-unit scale sequence stratigraphic models for prediction of sequence and systems tract-keyed facies architecture, continuity and connectivity (e.g., stacking patterns, N/G, facies object dimensions, directional variograms). Seismic attributes were used to predict facies and porosity continuity away from calibration wells in seismically-integrated cell-based models. Calibration models relating seismic response to porosity changes were developed utilizing 1) traditional, amplitude-based seismic attributes, 2) proprietary principle component attributes, 3) proprietary inflection segment attributes, and 4) total impedance inversion (the preferred approach).

A seismically-integrated cell-based model using a small subset of calibration wells was built in an effort to simulate an assessment project during field appraisal. Subsequently, conventional cell-based models were built using ranges of wellsets, ranges of sequence-specific facies proportions, and ranges of variogram models for SISIM stochastic facies modeling to simulate 40-, 20-, and 10-acre development drilling. These models highlight the importance of 3D seismic integration in the absence of wells early in field development, followed by outcrop analog integration as development proceeds.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil