From Bureau of Economic Geology, The
University of Texas at Austin (www.beg.utexas.edu).
For more information, please contact the author.
Bureau Seminar, February 21, 2014
video streaming of this seminar beginning at 8:55am February 21, 2014.
Description. Rock physics relationships are an essential element in the evaluation and modeling of seismic attributes for hydrocarbon exploration and appraisal. Calibration of seismic amplitude response
requires accurate prediction of the expected acoustic properties for reservoir rocks, non-reservoir
lithologies (e.g. mudrocks), and pore fluids at varying conditions. The estimation of seismic amplitude variation with offset (AVO), extraction of reservoir properties from seismic (inversion), and time-lapse (4D) seismic response are all similarly dependent on reliable rock and fluid property information.
Application. To ensure the effective integration of both field-scale (well-based) data and reservoir-specific calibration (core-based) measurements, we deploy a deliberate seismic petrophysics workflow. This workflow leverages traditional reservoir petrophysics data QC, integration (pressure, temperature, effective stress, and fluid acoustic properties), and quantitative formation evaluation as the front-end to an iterative rock physics model calibration workflow. Rock physics modeling, including shear log QC and forward modeling and fluid replacement scenarios, develops geophysically-specific products that extend reservoir petrophysics results (mineralogy, net-to-gross, porosity, saturation) to the seismic domain. The workflow can be applied to a single well or multiple wells, is amenable to inclusion of (global) analog data, and yields improved interpretive insights when utilized in an iterative manner.
Significance. Core analyses have long been seen as an essential component of geological reservoir description and source of essential petrophysical calibration data. Lab-based rock physics measurements, particularly (dynamic) P- and S-wave velocity data, form the basis for many empirical and heuristic rock physics models. Work with core-based data also affords the opportunity to measure (or infer) sample-specific textural properties that may have an impact on both petrophysical and elastic rock properties. The key to realizing maximum value from all core analyses is the recognition that petrophysical and geophysical measurements are complementary, and that all analytical results should consistently reflect the intrinsic geological characteristics of the porous media (grain size, sorting, coordination number, critical porosity, pore size/shape).
Results. In this presentation, we will review key details of the seismic petrophysics workflow, using data from several high quality siliciclastic well examples. Using several common heuristic and theoretical rock physics recipes, we will search for relevant textural signal(s) in both clastic and carbonate rocks, using a combination of lab- and well-based data sets. The vital role that reservoir petrophysics plays, within the context of an overall seismic petrophysics workflow, in bringing core-calibrated reservoir properties input to the modeling is highlighted throughout this discussion. Finally, we will also reflect on the challenges inherent in multi-scale data integration (core and log) and log-based methods for textural classification, and opportunities for increased utilization of quantitative tool-based forward modeling to resolve interpretation challenges at the interface between petrophysics and geophysics.