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The Perdido Fold Belt, Northwestern Deep Gulf of Mexico

A major research project, conducted from 1994 to 1996, involved the re-evaluation of the Perdido foldbelt in the northwestern deep Gulf of Mexico. This deep-water foldbelt rests in water depths of 7500-10,000 feet. This project consisted of a four-company industrial consortium (Shell, Texaco, Amoco, Mobil), who leased the mineral rights to the fold belt during the mid-1980's.

The companies pooled their proprietary seismic data bases ($5 million) and donated them to CU-Boulder, and paid us $220,000 for 2 years to evaluate the data. With the combined seismic data bases of the four companies, we remapped the structure and stratigraphy of the foldbelt in far greater detail, thus producing much more accurate maps for the companies. The results of the study contributed to the drilling of the Baha #1 well in Alaminos Canyon 600 from April to June 1996.  Spudded in 7612 feet of water, the well experienced drilled problems and TD'ed at a depth of 3596 feet.  The well was classified an order 4 well by the MMS (i.e. 14 feet of producible petroleum).  A second well was drilled in the Baha structure (AC 557) in late 2000/early 2001. Results remain confidential.

In July 2001, Unocal announced a major discovery in AC 903 (Trident)(9678 feet water). They reported 300 feet of pay sands, in up to 12,000 acres of closure. A stepout evaulation well was drilled from October 2001 to January 2002 in 9712 feet of water. by Unocal and partners. Two other wells have had plans-of-exploration (POE's) submitted to the MMS. Shell has announced they will drill the White Shark prospect in early 2002, and ChevronTexaco have indicated they will drill a subsalt well northeast of the Baha structure in 2002. Finally, Pemex has announced that they plan to drill a well testing the Perdido foldbelt in Mexican waters sometime in 2002 or 2003. The structural highest folds are in Mexican waters. Clearly, the Perdido Foldbelt has the potential of being a signifcant play in the northwestern deep Gulf of Mexico.

Listed below is a summary of papers published from this project and the abstracts with a few figures from two recent papers published in the AAPG Bulletin.


Selected References


AAPG Bulletin, v. 83, 88-113.

The Perdido Fold Belt, Northwestern Deep Gulf of Mexico, Part 1: Structural Geometry, Evolution and Regional Implications

Bruce D. Trudgill, Mark G. Rowan, J. Carl Fiduk, Paul Weimer, Peter E. Gale, Bryant E. Korn, Ronald L. Phair, William T. Gafford, Geneva R. Roberts, and Steven W. Dobbs

ABSTRACT

The Perdido fold belt is a frontier petroleum exploration province located in deep waters of the northwestern Gulf of Mexico. The anticlines are NE-SW trending, symmetrical to asymmetrical, concentric folds usually bounded on both flanks by steep reverse faults. They are interpreted as detachment folds cored by autochthonous Middle Jurassic Louann salt. The fold belt overlies rifted transitional crust characterized by NE-SW trending basement highs and NW-SE transverse structures that controlled the original salt thickness and subsequent fold geometry.

Upper Jurassic through Eocene strata were folded during the early Oligocene (36 to 30 Ma), with deformation possibly continuing into the earliest Miocene. Post-kinematic sediments gradually buried the folds, with younger strata progressively onlapping the highest structures. Some folds were reactivated during the middle Miocene, and a late phase of broad uplift during the Plio-Pleistocene is attributed to loading of the Louann salt by the advancing Sigsbee salt nappe.

The Perdido fold belt marks the basinward margin of a complex, linked system of gravitational spreading above salt. Updip Paleogene sedimentary loading and associated extension were accommodated downdip primarily by salt canopy extrusion. The 5-10% shortening and folding occurred only after canopy feeders were evacuated and closed off. Subsequent loading and deformation were concentrated at higher, allochthonous levels.

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Regional map of northern Gulf of Mexico showing the three Cenozoic Fold belts and extent of allochthonous salt (Click to enlarge)

Depth conversion and sequential (B-D) two-dimensional restorations of a northwest-southeast seismic profile across Perdido fold belt (Click to enlarge)

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Regional time-structure map at MCSB (middle Cretaceous sequence boundary) level, showing the regional northeast-southwest trend of the fold structures and bounding reverse faults  (Click to enlarge)

Northwest-southeast seismic profile BB' across fold 3c in the northern part of the fold belt and the frontal folds 1 and 2b (Click to enlarge)


AAPG Bulletin, v. 83, 578-610

The Perdido Fold Belt, Northwestern Deep Gulf of Mexico, Part 2: Seismic Stratigraphy and Petroleum Systems

Joseph C. Fiduk, Paul Weimer, Bruce D. Trudgill, Mark G. Rowan, Peter E. Gale, Ronald L. Phair, Bryant E. Korn, Geneva R. Roberts, William T. Gafford, Roger S. Lowe, and Tomas A. Queffelec

ABSTRACT

Analysis of 12,000 km of 2-D multi-fold seismic data shows a thick succession of Mesozoic and Cenozoic deep-water strata in the Perdido fold belt, northwestern deep Gulf of Mexico. These strata differ in seismic facies, areal distribution, and reservoir/petroleum potential. Mesozoic strata are interpreted as dominantly fine-grained carbonates and show minor thickness changes. Cenozoic strata are largely mud-dominated siliciclastic turbidity deposits and vary considerably in thickness across the fold belt. These changes reflect the shifting position of Cenozoic marginal marine depocenters.

Mesozoic reservoir potential consists of fractured Upper Jurassic and Cretaceous deep-water carbonates. Cenozoic reservoir potential consists of siliciclastic deep-water turbidites. Portions of the Paleocene to lower Eocene strata are sand-prone and are the down-dip equivalents of the lower and upper Wilcox shallow-marine depocenters. These strata are all incorporated within the folds. Lower to middle Oligocene strata coincide with the main growth phase of the fold belt. Potentially sand-prone middle Oligocene to lower Miocene strata are the down-dip equivalents of the Vicksburg (early Oligocene), Frio (Oligocene), and Oakville (early Miocene) shallow-water depocenters. These strata form potential stratigraphic traps against the folds.

Mesozoic source potential was modeled assuming Oxfordian, Tithonian, Barremian, and Turonian source beds. 1-D thermal maturation modeling showed these sources reached peak oil generation between 51-39 Ma, 39-8 Ma, 32-2 Ma, and 26-8 Ma, respectively. Cenozoic source potential was modeled using an Eocene source. Modeling showed this source only reached early oil generation in the basinward half of the fold belt. Thermal maturation was reached by source beds at different times in different locations due to changes in burial depth, amount of structural uplift, and underlying thickness of autochthonous salt. All these factors indicate that seal and reservoir carry significant risk, but that the potential exists for large petroleum accumulations.

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Cross section (in depth) through Alaminos Canyon showing present day distribution of thermal maturity windows (Click to enlarge)

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Geohistory plots (from BasinMod) at locations 1 and 8 with thermal maturation overlay. Difference in maturation history reflect variations in depth of burial, structural uplift, and volume of underlying autochthonous salt (Click to enlarge)