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Recent applications of AVO to carbonate reservoirs in the Western Canadian Sedimentary Basin

Core Laboratories Reservoir Technologies Division, Calgary, Alberta, Canada

Bill Goodway

EnCana Corporation, Calgary, Alberta, Canada

Corresponding author: yli@corelab.ca

The first 20% of the full text of this article appears below.

Carbonates make up about half of the sedimentary rock in the Western Canada Sedimentary Basin (WCSB) and range from Cambrian to early Jurassic in geologic age. Large oil and gas reserves exist in Devonian and Early Carboniferous carbonate formations. Middle and Upper Devonian carbonate rocks alone have known reserve of about 15 billion barrels of oil and 35 trillion cubic feet of natural gas. A variety of carbonate reservoirs exist in the WCSB, mostly reef and platform types. These reservoirs are formed by porous limestones or platforms that were dolomitized prior to basin-wide hydro-carbon maturation and migration. Fractured reservoirs were formed by natural fractures due to regional or local stress regimes or by local overpressure.

Until recently, seismic analysis of data from carbonate reservoirs relied mainly on interpreting zero-offset (stacked) volumes. Common knowledge within the world of AVO suggests that zero-offset information is often insufficient to differentiate shale from carbonate porosity, or to discriminate gas-saturated from brine-saturated reservoirs. However, in the last a few years, great efforts have been made to apply AVO analysis to carbonate reservoir characterization but several issues must be addressed in investigating the feasibility, potential, and sensitivity of the response of carbonate rock properties to porosity and fluid.

First, a lack of carbonate rock property information is considered an obstacle in applying AVO to carbonate reservoir characterization. Second, the differences between clastic AVO and carbonate AVO need to be clarified. Third, procedures and calibration in seismic data processing and interpretation need to be developed. The situation has been greatly improved due to recent significant acquisition of dipole sonic logs that sample a variety of reservoirs and formations directly associated with carbonates. This newly acquired information provides in-situ reservoir and nonreservoir measurements that are beyond laboratory and theoretical rock property predictions. On the seismic side, experience in . . . [Full Text of this Article]

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