Importance of Detailed Sequence Stratigraphic Correlations to the Field Development of “Stacked” Shelf-Margin Reservoirs: Vacuum Abo Unit, Lea County, New Mexico, U.S.A
Ryan Phelps1, Steven L. Bachtel2, and Jonathan A. Woolley2
1Jackson School of Geosciences, The University of Texas, Austin, TX
2Subsurface Technology, ConocoPhillips Co., Houston, TX
Optimized recovery of hydrocarbons in carbonate shelf margin reservoirs requires an understanding of facies heterogeneity at multiple scales. Many times, large-scale lithostratigraphic units are used to define producing units. Correlation of lithologic contacts, and resulting porosity and structure maps derived from these surfaces, create false structural highs and provide an impression of homogeneous facies and reservoir character. This tends to mask potential flow barriers present at smaller scales. A case study of the Permian (Leonardian) Vacuum Abo Unit demonstrates the need for data integration within a higher-order chronostratigraphic framework.
Three Abo Formation cores illustrate three environments each with distinct cycle types, including (1)peritidal platform interior,(2)high-energy shelf margin(reservoir), and (3)slope to basin. Core descriptions and facies types are calibrated to gamma ray logs and correlated across the depositional profile. Seven high-frequency sequences are present in the Abo Formation, each with numerous high-frequency cycles. Sequence boundaries correlations reveal a basinward dipping stratigraphic architecture that contrasts with a high-relief mounded geometry (Abo “reef”) created by previous lithologic correlations. Within the grain-dominated packstone and grainstone of the shelf-margin reservoir zone (high interparticle porosity, good permeability), interbeds of muddy tidal flat capped cycles (progradation during highstands) and muddy fusulinid packstone based cycles (retrogradation during transgression) create numerous potential flow barriers. The muddy fusulinid packstone has high porosity on electric logs; however the porosity is moldic and has very low permeability creating potential flow barriers. Net porosity maps based solely on well logs should be used with caution when evaluating development plans and economic potential.
AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery