CARBONATE PLAY DEVELOPMENT IN MESOZOIC SEQUENCES OF THE U.S. GULF RIM
Influence of Physiographic Setting and Structural Controls
FOR
EAST TEXAS GEOLOGICAL SCOIETY
Jeffrey J. Dravis Ph D
Dravis Geological Services, Houston, Texas
February 23 & 24, 2023
Tyler, Texas
SEMINAR OVERVIEW
Most of industry has ignored conventional carbonate plays for years, as higher commodity prices drove the development of unconventional (mostly shale) plays. However, conventional carbonate plays remain a viable economical alternative.
A conventional carbonate play is the juxtaposition of a limestone or dolostone reservoir facies sealed by a micritic carbonate or shale facies, with its hydrocarbons sourced from a nearby organic-rich carbonate or siliciclastic mudstone. Understanding the controls on carbonate play type distribution and geometry is critical for more successful exploration or exploitation in any basin. Hence, delineating potential carbonate plays from seismic or wireline logs requires a sound understanding of the depositional and diagenetic controls that create the reservoir facies. These controls must be evaluated within the context of physiographic setting and the structural framework. Specifically, one must appreciate the environmental controls on carbonate facies development, and the potential pathways for diagenesis and porosity evolution, some of which can be tied to the influence of reactivated basement faults.
This two-day seminar reviews the key controls on Jurassic and Cretaceous carbonate play occurrence and distribution along the U.S. Gulf of Mexico rim, while also documenting the strong influence of physiographic setting, both at the global and local scale. On a global scale, physiographic setting refers to the location of a prospective basin or sub-basin with respect to the paleoequator. Such a position determines the prevailing paleotrade wind systems, which were a critical influence on carbonate sedimentation and play distribution. In this region, Mesozoic carbonate facies with reservoir quality occurred within tropical or subtropical settings, and easterly paleotrade winds often were a major influence on their occurrence and distribution. On a local scale, physiographic 2 setting refers to the depositional bottom topography associated with a platform or ramp profile. This preexisting bottom topography critically controls the occurrence and distribution of carbonate facies and also early diagenesis. In addition, progressive burial diagenesis influenced their porosity and permeability evolution, with deep-seated faulting often playing a major role in the development of reservoir quality, as well as hydrocarbon entrapment. Therefore, understanding the relative timing of secondary porosity development in these carbonates is often the key to exploiting regional porosity trends, and this point will be stressed in this seminar.
This seminar ends with a detailed evaluation of the attributes (reservoir, source, seal, and trapping mechanism) of conventional Mesozoic carbonate play types along the northern U.S. Gulf rim. These plays are related to physiographic setting and illustrated with representative reservoir analogs. This discussion is backed by rock-based observations and examples that note the various pathways for porosity and permeability evolution, as well as the timing of reservoir development. Seismic attributes are noted, where possible. For most play type case studies, their relationship to regional and/or local structural influences are established, since structuring could initiate the play, help control porosity evolution, set up the trap, or do all three things.
Case studies of Mesozoic carbonate plays discussed in this seminar include:
Jurassic: Smackover; Haynesville (aka, Gilmer or Cotton Valley Limestones) and Knowles (?)
Lower Cretaceous: Sligo; James Limestone; Glen Rose; Edwards; and Knowles (?)
Upper Cretaceous: Brief review of depositional chalk plays*
The ultimate goal of this seminar is to provide participants with guidelines and procedures that enhance their ability to exploit a particular play concept in other areas
around the U.S. Gulf of Mexico rim.
*NOTE: I present a separate one-day, in-depth seminar on the Austin Chalk trend in Texas and Louisiana, if you want a more detailed discussion of depositional chalk plays than I have time for in this seminar (next Austin Chalk Seminar will be held on February 8, 2023 as an online Zoom seminar).
SCHEDULE
FEBRUARY 23, 2023
8:30 Presentation 1: Introduction & Distinctive Aspects
9:30 Coffee Break
9:45 Presentation 2: Limestone Diagenesis and Porosity Evolution: Controls,
Processes and Products; Timing Relationships
11:30 Presentation 3: Requirements for Dolomitization; Dolomitization Models
12:00 Lunch
1:00 Presentation 3: Evolution of Porosity and Permeability in Dolostones
(Continued)
2:00 Coffee Break
2:15 Presentation 4: Carbonate Facies: Attributes; Controls on Occurrence and
Distribution – Continued (with short breaks)
4:30 Adjourn
FEBRUARY 24, 2023
8:30 Presentation 4: Carbonate Facies: Ramp Model
9:15 Presentation 5: Key Stratigraphic Relationships in Carbonates
10:15 Coffee Break
10:30 Presentation 6: Selected Mesozoic Carbonate Plays: Attributes and Case
Studies from the U.S. Gulf Rim (with short breaks)
12:00 Lunch
1:00 Carbonate Plays (Continued)
2:00 Coffee Break
2:15 Carbonate Plays (Continued; with short breaks)
4:30 Seminar Ends
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