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AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain

Geological Heterogeneity in the Wafra First Eocene Reservoir, Partitioned Neutral Zone (PNZ) - Implications for Steamflood Development

William S. Meddaugh1; Niall Toomey1; Willaim Dawson1; William T. Osterloh1; David Barge1

(1) Chevron, Houston, TX.

The Paleocene/Eocene age First Eocene dolomite reservoir at Wafra Field in the PNZ (Saudi Arabia and Kuwait) is estimated to hold more than 10 billion barrels of 18-22 API, high sulfur oil. Current estimates suggest that only 5-10% of the OOIP may be produced during primary development. Consequently, steam flooding is being investigated as an appropriate secondary development option. A pilot consisting of single, very small 5-spot pattern with center injector has been used to demonstrate long term steam injectivity as well as to evaluate aspects of the reservoir response to steam injection. Critical to the economic success of the project will be a thorough understanding of the impact of both areal and vertical reservoir heterogeneity on steam migration. Analysis of temperature and petrophysical logs obtained in a temperature observation well located 35 feet from the injector have showed that a vertical barrier to steam migration exists approximately 80 feet above the base of the completions in the injector. Two, relatively thick (5-10 feet), very low porosity and very low permeability evaporite-rich zones (mainly coalesced nodular to possibly bedded anhydrite with some gypsum) that were regarded as the most likely barriers prior to the start of steam injection did not act as barriers. Rather, an interval characterized by numerous thin, variously cemented (including celestite and native sulfur cements), exposure surfaces or hardgrounds seems to provide the vertical barrier. This zone is also characterized by generally low porosity and low permeability as well as very light oil stain. Detailed studies, including micro-permeameter measurements, thin section analysis, and quantitative mineralogical studies, are being used to further characterize the steam barrier interval. The geological and stratigraphic assessments of heterogeneity are supplemented by a history-matched thermal simulation model that suggests that the evaporite-rich zones may have acted as short term baffles but that the “ultimate” barrier is coincident with the interval characterized by abundant exposure surfaces or hardgrounds.