Exploration and Production Technologies
Integrated Geological-Engineering Model for Reef and Carbonate Shoal Reservoirs Associated with Paleohighs: Upper Jurassic Smackover Formation, Northeastern Gulf of Mexico

DE-FC26-00BC15303

Program
This project was selected in response to DOE's Oil Exploration and Production solicitation DE-PS26-01NT41048 (focus area: Critical Upstream Advanced Diagnostics and Imaging Technology). The goal of the solicitation was to promote cross-cutting technologies for imaging and quantifying reservoir rock and fluid properties for improved oil recovery.

Project Goal
To increase the profitability, producibility, and efficiency of the recovery of oil from existing and undiscovered Upper Jurassic Smackover reservoirs and fields characterized by reef and carbonate shoals associated with pre-Mesozoic basement paleohighs.

Performers
University of Alabama
Tuscaloosa, AL

Texas A&M University
College Station, TX

McGill University
Montreal, Canada

Longleaf Energy Group
Brewton, AL

Strago Petroleum Corporation
Houston, TX

Paramount Petroleum Company
Jackson, MS

Project Results
Geoscientific reservoir property, geophysical seismic attribute, petrophysical property, and engineering property characterization have shown that reef and shoal reservoir lithofacies developed on the flanks of high-relief crystalline basement paleohighs (Vocation field) and on the crest and flanks of low-relief crystalline basement paleohighs (Appleton field). Geologic modeling and reservoir simulation indicate that little oil remains to be recovered at Appleton field and a significant amount of oil remains to be recovered at Vocation field through a strategic infill drilling program.

Benefits
The complex nature of carbonate reservoirs makes the design of successful exploration strategies and of cost-effective development scenarios difficult for these rocks. The understanding of the rock and fluid characteristics that affect the reservoir properties of these rocks serves to improve techniques for reservoir detection, characterization, and development.

The completion of this project has resulted in an improved understanding of the geological, geophysical, petrophysical, and engineering properties of reef-shoal reservoirs emphasizing Appleton and Vocation fields in southwest Alabama. An integrated geological model based on these properties has been developed to facilitate exploration for reef-shoal reservoirs and to enhance development of reef-shoal reservoirs in existing fields. This information has been transferred to the operators of Appleton and Vocation fields and to other independents operating in the eastern Gulf Coastal Plain area through technology workshops. The findings of this project have the potential to result in increased oil producibility from existing and newly discovered fields similar to Appleton and Vocation fields.

Background
The Upper Jurassic Smackover Formation is one of the most prolific hydrocarbon reservoirs in the northeastern Gulf of Mexico. Although production from Smackover fields totals 1 billion barrels of oil and 4 trillion cubic feet of natural gas, much of the oil in these fields remains unrecovered because of a lack of a complete understanding of the rock and fluid characteristics that affect reservoir architecture, heterogeneity, quality, fluid flow, and producibility. This problem is compounded because of inadequate techniques for reservoir detection and the characterization of rock fluid interactions, as well as imperfect models for fluid flow prediction.

In addition, independent operators dominate the development and management of these fields in the Eastern Gulf Coastal Plain. These companies do not have the financial resources and/or staff expertise to improve substantially the understanding of the geoscientific and engineering factors affecting the producibility of Smackover carbonate reservoirs, which makes research and application of new technologies for reef-shoal reservoirs all that more important.

Project Summary 
Among the project's accomplishments:

  • Geoscientific reservoir property, geophysical seismic attribute, petrophysical property, and engineering property characterization have shown that reef (thrombolite) and shoal reservoir lithofacies developed on the flanks of high-relief crystalline basement paleohighs and on the crest and flank of low-relief crystalline basement paleohighs.
  • Reef thrombolite lithofacies have higher reservoir quality than shoal lithofacies due to overall higher permeabilities and greater interconnectivity.
  • Reef thrombolite dolostone flow units, which are dominated by dolomite intercrystalline and vuggy pores, are characterized by a pore system comprising a higher percentage of large-sized pores and larger pore throats.
  • Rock fluid interactions (diagenesis) studies have shown that although the primary control on reservoir architecture and geographic distribution of Smackover reservoirs is the fabric and texture of depositional lithofacies, diagenesis (dolomitization) is a significant factor that preserves and enhances reservoir quality.
  • Geologic modeling, reservoir simulation, and testing and applying the resulting integrated geologic-engineering models have shown that little oil remains to be recovered at Appleton field and a significant amount of oil remains to be recovered at Vocation field through a strategic infill drilling program.
  • The water-drive mechanisms for primary production in Appleton and Vocation fields remain effective; therefore, the initiation of a pressure maintenance program or enhanced recovery project in these fields is not required at this time.
  • The integrated geologic-engineering model developed for a low-relief paleohigh was tested for three scenarios involving the variables of present-day structural elevation and the presence or absence of potential reef thrombolite lithofacies. The predictions based upon the model were correct.
  • From the integrated modeling, the characteristics of the ideal prospect in the basement ridge play include a low-relief paleohigh associated with a thrombolite doloboundstone and dolostone that has sufficient present-day structural relief so that these carbonates rest above the oil-water contact.

Current Status
The findings from these projects are being used to characterize and model the thrombolite and shoal reservoirs at Little Cedar Creek field, a recent Smackover discovery in southwest Alabama.

High-relief paleohigh and associated microbial reef facies model (Vocation field).

Low-relief paleohigh and associated microbial reef facies model (Appleton field).

Publications (selected)
Four annual DOE Project Technical Reports.

Morgan, D., Mapping and ranking flow nits in reef and shoal reservoirs associated with paleohighs: Upper Jurassic (Oxfordian) Smackover Formation, Appleton and Vocation fields, Escambia and Monroe Counties, Alabama, M.S. thesis, Texas A&M University, 157 p., 2003

Parcell, W.D., Evaluating the development of Upper Jurassic reefs in the Smackover Formation, eastern Gulf Coast, U.S.A., through fuzzy logic computer modeling, JSR, Volume 71, p. 498-515, 2003

Tebo, J.M., Use of volume-based 3-D seismic attribute analysis to characterize physical property distribution: a case study to delineate reservoir heterogeneity at the Appleton field, S.W. Alabama, M.S. thesis, McGill University, 169 p., 2003

Mancini, E.A., Llinas, J.C., Parcell, W.C. Aurell, M., Bedenas, B., Leinfelder, R.R., and Benson, D.J., Upper Jurassic thrombolite reservoir play, northeastern Gulf of Mexico, AAPG Bulletin, Volume 88, pp. 1573-1602, 2004

Project Start: September 1, 2000
Project End: December 31, 2003

Anticipated DOE Contribution: $754,000
Performer Contribution: $542,000 (42% of total)

Contact Information
NETL - Virginia Weyland (virginia.weyland@netl.doe.gov or 918-699-2041)
University of Alabama - Ernest Mancini (emancini@wgs.geo.ua.edu or 205-348-4319)

 
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