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Carbonate Reservoir Delineation from Seismic Data – Examples of Crosswell Seismic*

By

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).

Click to view list of articles adapted from presentations by P.M. (Mitch) Harris or by his co-workers and him at AAPG meetings from 2000 to 2008.

¹ Chevron Energy Technology Company, 6001 Bollinger Canyon Road, San Ramon, CA ([email protected])

Abstract

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.