Carbonate Reservoir Delineation from Seismic Data – Examples of Crosswell Seismic*
Paul M. (Mitch) Harris1
Search and Discovery Article #40299 (2008)
Posted August 26, 2008
*Adapted from oral presentation at the 2006 AAPG International Conference and Exhibition, Perth, Australia, November 5-8, 2006. See companion article, "Crosswell Seismic in Carbonate Reservoirs – High-Resolution Reservoir Delineation," Search and Discovery Article #40307 (2008).
1 Chevron Energy Technology Company, 6001 Bollinger Canyon Road, San Ramon, CA ([email protected])
Crosswell seismic tomography provides better reservoir resolution than surface data; therefore there should be value added in reservoir delineation. Examples of crosswell seismic data from two fields illustrate the resolution and some potential applications of this type of data: (1) defining greater geologic detail between wells (heterogeneity of reservoir), (2) recognizing laterally continuous zones for improved development (well positioning, completions, injection), and (3) input for reservoir models (layering and assigning porosity).
In the first example, the producing formation is limestone with minor dolomite and shale. 3D seismic and down hole log data suggest lateral discontinuities, but details are ambiguous due to the poor resolution. Crosswell data defines the nature of some of the reservoir discontinuity, in that clinoforms which are imaged can potentially isolate reservoir compartments. A comparison with outcrop facies geometries provides some sense of the reservoir facies to be expected between wells.
The second example is a diagenetically complex cyclic shelf dolomite. Variations in amplitude on the crosswell data are the most striking lateral features, and nearly every positive-amplitude event coincides with a significant increase in velocity on sonic logs. Both the seismic and log data respond to the same diagenetic overprint and its resulting petrophysical characteristics; therefore log-derived facies relate to the crosswell data better than core lithofacies. Comparing crosswell data with geostatistical porosity models and with analogous outcrops to further analyze the potential imaging of lateral porosity variation suggests lateral changes in porosity are being imaged at the scale of tens of meters.
Eisenberg, R.A., and P.M. Harris, 1994, Application of chemostratigraphy to differentiating bounding stratigraphic surfaces: AAPG 1994 Annual Meeting Abstracts, p. 143.
Martin, R.L., C.L. Welch, G.D. Hinterlong, J. Meyer and R. Evans, 2002, Using crosswell seismic tomography to provide better reservoir resolution in the Wolfcamp Formation in Lea County, New Mexico: in The Permian Basin; Preserving Our Past – Securing Our Future, West Texas Geological Society #02-111, p. 25-34.
Tucker, K.E., P.M. Harris, and R.C. Nolen-Hoeksema, 1998, Geologic investigation of cross-well seismic response in a carbonate reservoir, McElroy field, West Texas: AAPG Bulletin, v. 82/8, p. 1483-1503.