2015 GOM Basin Paleoenvironmental Well Geohistory and Sequence Map Sub-Database
This new exploration toolset includes Paleobathymetric Ecozone, Lithobiofacies, Estimated Sand Percent, and Estimated Gross Sand Accumulation Rate sequence maps for each of the 46 Cenozoic Gulf of Mexico Chronostratigraphic Sequences. The addition of this new sub‐database to the 2015 Comprehensive Gulf of Mexico Chronostratigraphic Sequence and Deposystem Maps Database is designed to complement our regularly provided and updated Sequence Accumulation Rate Maps, and our other useful deposystem map products. These new maps and data will further enhance your ability to locate, assess and risk siliciclastic reservoir systems across the Gulf Basin.
The paleoenvironmental sub‐database supplement is intended to provide additional inexpensive, welldata driven, predictive exploration tools for identifying untapped or under‐tapped exploration targets with high potential, to support seismic play confirmation, and to provide information on regional depositional trends such as sediment transport pathways, in support of prospect and lease evaluations.
These maps, derived from underutilized benthic foraminiferal paleoecologic datasets, provide brand new and exciting paleoenvironmental views of the GOM deposystem.
BENTHIC FORAMINIFERAL "PALEOBATHYMETRIC ECOZONE" SEQUENCE MAPS
Paleobathymetric ecozones are identified based on the presence of unique assemblages of benthic foraminifera whose habitat preferences are linked is various ways to paleo water depth. Traditionally an important component of the regional reservoir risk assessment tool kit, paleoecozone maps reveal the distribution of water depth related benthic sub‐environments of the shelf, slope and deep basin.
BENTHIC FORAMINIFERAL “LITHOBIOFACIES” SEQUENCE MAPS
Lithobiofacies are depositional facies identified based on the presence of certain benthic foraminiferal index taxa known to be sensitive to specific depositional environments and the sediment types deposited within such environments. Lithobiofacies maps go a step beyond paleoecozone maps, capitalizing on the dual utility of many foraminiferal paleoecozone index taxa to also identify specific lithobiofacies that convey information on reservoir properties critical to a successful exploration program, e.g., grain‐size.
Lithobiofacies maps clearly reveal the distribution of reservoir‐prone and barrier‐prone sedimentary units. The identification, mapping and analysis of lithobiofacies provide unique qualitative insights into the distribution of reservoir section through time. Associated digital datasets provide a basis for direct comparison with digital geological, petrophysical and engineering datasets to provide reservoir risking teams with multidisciplinary perspectives on which to base effective exploration and reservoir development strategies.
EVIDENCE OF THE LINK BETWEEN PALEOECOZONES AND LITHBIOFACIES
The close relationship between paleoecozones and lithobiofacies can be demonstrated by plotting the number of ecozone index taxa that are also identified as lithobiofacies index taxa. For example: a very high proportion of paleoecozone2 (inner neritic) index taxa are also identified as siliciclastic deltaic lithobiofacies index taxa, while a very high proportion of paleoecozone 3 (middle neritic) index taxa are also identified as prodeltaic lithobiofacies index taxa, and a very high proportion of paleoecozone 4 (outer neritic) index taxa are also identified as distal prodeltaic‐hemipelagic lithobiofacies index taxa.
Similar relationships are seen for paleoecozone 5 and 6 (upper and lower bathyal) index taxa which share very high proportions of confined and unconfined hemipelagite lithobiofacies index taxa respectively.
RELATIONSHIP BEWEEN FORAMINIFERAL LITHOBIOFACIES AND RESERVOIR PROPERTIES
Research carried out by Earth Studies Group has demonstrated that benthic foraminiferal lithobiofacies are related directly to sediment type, and accordingly to reservoir risk. Studies were carried out on both research boreholes and wells in producing fields. Abundant data comparisons provide direct evidence of a strong correspondence between lithobiofacies and sedimentary properties relating to reservoir and flow‐barrier or sealing potential.
- Common siliciclastic lithobiofacies of the northern and central Gulf Basin have been ranked according to reservoir and seal potential (Fillon, 2009).
- Cross plots of lithobiofacies vs. reservoir properties such as grain‐size and permeability have revealed lithobiofacies to be predictive of reservoir quality and efficiency in producing fields (Fillon et al., 2003).
'ESTIMATED PERCENT' SAND AND 'ESTIMATED GROSS' AND ACCUMULATION RATE SEQUENCE MAPS
Another important component of the regional reservoir risk assessment tool kit are sequence maps of estimated percent sand, where percent sand estimates are assigned to recognized lithobiofacies based on the inspection of lithobiofacies vs. percent sand plots for research boreholes and wells in producing fields.
Estimated percent sand sequence maps benefit explorationists in two ways. The first is obvious, by providing views of the distribution of dominantly sand‐rich and dominantly sand‐poor strata contained within each Cenozoic chronosequence. The second way that estimated percent sand maps benefit explorationists is that they provide a basis for creating estimated gross sand accumulation rate sequence maps, which are produced by multiplying each estimated sand percentage map grid by its age‐equivalent sequence accumulation rate map grid.
Comparison of lithobiofacies‐predicted higher sand accumulation rate depopods, e.g., for GOM chronosequence 19 (“Big Hum”) in Mississippi Canyon, with “Big Hum” producing fields, shows that lithobiofacies‐predicted higher sand accumulation rate depopods correspond closely to well log indicated gross sand thicknesses in the field wells.