AAPG/Datapages Discovery Series (CD-ROM) No. 1
ABSTRACT: Overview of the Depositional Styles by Chronozone of the Northern Gulf of Mexico
By David A. Marin, United States Department of Interior, Minerals Management Service, Katherine M. Ross, United States Department of Interior, Minerals Management Service, Barbara J. Bascle, United States Department of Interior, Minerals Management Service, Lesley D. Nixon, United States Department of Interior, Minerals Management Service

Copyright © 2000 by The American Association of Petroleum Geologists
Originally presented at the 1998 Hedberg (AAPG) Research Conference at Galveston, TX
Book/CD-ROM Title: Integration of Geologic Models for Understanding Risk in the Gulf of Mexico (2000).
Edited by Robert Shoup, Joel Watkins, John Karlo, and Dave Hall

The Minerals Management Service (MMS), U.S. Department of the Interior, has classified the producible sands from the approximately 1,100 fields across the northern Gulf of Mexico into groups of genetically related plays defined by production, chronostratigraphy, lithostratigraphy, depositional style, and structure. Products resulting from this work are the Atlas of Northern Gulf of Mexico Gas and Oil Reservoirs (Seni et al.,1997 and Hentz et al., 1997) and Assessment of the Conventionally Recoverable Hydrocarbon Resources of the Gulf of Mexico and Atlantic Outer Continental Shelf (Lore et al., to be published). The offshore Atlas project provided the basic framework for play definition used by MMS. The assessment project utilizes the play concept to further evaluate and provide an estimate for undiscovered resources in the Gulf of Mexico

The MMS defined chronozones in the northern Gulf of Mexico on the basis of benthic foraminifera stratigraphic zones. The 26 chronozones identified by Reed et al.(1987) were further grouped into 15 Cenozoic and 3 Mesozoic chronozones for correlation purposes (figure 1) Type logs for each field in the Gulf of Mexico were constructed. Each type log is a composite of field wells showing all productive sands and their chronostratigraphic relationship. Not only were the productive sands organized by chronozone, but, based on SP log characteristics, paleoecozones, and sand content, they were also characterized by retrogradational, aggradational, progradational, and fan depositional styles. (figure 2). The chronozones and depositional styles identified on each type log were then correlated among the fields across the Gulf of Mexico. All productive sands correlated to the same chronozone and depositional style or structural setting define a unique play.

Assessment play maps for each chronozone build upon the proved reserves play limits illustrated in the offshore Atlas by including major unproved field reserves. In addition, for each play, known hydrocarbon and sand limits based on additional wells with either hydrocarbon shows or sand development, respectively, are shown.

The assessment play maps provide an organizational framework for exploration analogs in the Gulf of Mexico. Understanding the relationships of the different depositional styles allows the user to characterize reservoirs in relation to sand content and geographic extent. This knowledge further allows the user to identify the most prolific reservoir types, their locations, and the areas most favorable for future discoveries.

Figure 1. Gulf of Mexico MMS geologic time scale.

Figure 2. Model for deltaic deposition.