Improving Reservoir Characterization of Karst-Modified Reservoirs with 3-D Geometric Seismic Attributes

Susan E. Nissen¹, E. Charlotte Sullivan², Kurt J. Marfurt³, and Timothy R. Carr⁴. (1) Consultant, McLouth, KS, (2) Pacific Northwest National Laboratories, Richland, WA, (3) Allied Geophysical Laboratories, University of Houston, Houston, TX, (4) Kansas Geological Survey, The University of Kansas, Lawrence, KS  [email protected]

Reservoir production and compartmentalization in many karst-modified reservoirs can be related to features resulting from subaerial weathering, tectonic faulting and fracturing, and/or hydrothermal processes. Critical features relating to reservoir character are often subtle and are difficult to image with standard seismic attributes. New 3-D seismic-based geometric attributes, including volumetric curvature and rotation attributes, have the potential, when calibrated with geologic and engineering data, to image and quantify karst-modified reservoir features at an interwell scale not previously possible.

We have applied these new seismic attributes to reservoirs in Kansas, Colorado, and Texas that represent a diversity of ages, lithologies, karst processes, and porosity/permeability systems. In these reservoirs, we have mapped horizon structure, faults, and fractures with a combination of conventional seismic data, coherency, and new volumetric-curvature attributes. Using horizon extractions and time slices, we have imaged the geomorphology of eroded surfaces. Features observed with geometric seismic attributes include sinkholes/collapse features, polygonal features, and sets of oriented lineaments. These features potentially have various geological origins, which affect how they should be incorporated into reservoir models. Timing of origin, in particular, has a significant effect on whether features contribute positively or negatively to reservoir performance.

Using our experience with 3-D geometric seismic attribute in these reservoirs, we have developed a seismic-based interpretation workflow for reservoir characterization of karst-modified reservoirs, in which features identified using 3-D seismic attributes are integrated with geologic data to classify the type of karst overprint. This methodology can provide insight on origin of the observed features and allows us to predict their effect on reservoir performance. 3-D attributes can help resolve uncertainties in reservoir quality, compartmentalization, and seal integrity.