Robert M. Mink

Norphlet Formation (Upper Jurassic) of Southwestern and Offshore Alabama: Environments of Deposition and Petroleum Geology

Upper Jurassic Norphlet sediments in southwestern and offshore Alabama accumulated under arid climatic conditions. The Appalachian Mountains of the eastern United States extended into southwestern Alabama to provide a barrier for air and water circulation during the deposition of the Norphlet Formation. These mountains produced topographic conditions that contributed to the arid climate, and they affected sedimentation. Norphlet paleogeography in southwestern Alabama was dominated by a broad desert plain, rimmed to the north and east by the Appalachians and to the south by a developing shallow sea. The desert plain extended westward into eastern and central Mississippi. Norphlet sedimentation initiated as a result of basin subsidence accompanied by erosion of the southern Appalachians. Norphlet conglomerates were deposited in coalescing alluvial fans in proximity to an Appalachian source. The conglomeratic sandstones grade downdip into red beds that accumulated in distal portions of alluvial fan and wadi systems. Quartz-rich sandstones were deposited as dune and interdune sediments on a broad desert plain. The principal source of the sand was updip alluvial fan and plain and wadi deposits. Wadi and playa lake sediments also accumulated in the interdune areas. A marine transgression was initiated during the late phase of deposition of the Norphlet Formation, resulting in the reworking of previously deposited Norphlet sediments. Norphlet hydrocarbon potential in southwestern and offshore Alabama is excellent; six oil and gas fields already have been established. Petroleum traps discovered to date are primarily structural traps involving salt anticlines, faulted salt anticlines, and extensional fault traps associated with salt movement. Reservoir rocks consist primarily of quartz-rich sandstones that are eolian, wadi, and marine in origin. Porosity is principally secondary (dissolution) with some intergranular porosity. Smackover algal carbonate mudstones were probably the source for the Norphlet hydrocarbons. Jurassic oil generation and migration probably were initiated in the Early Cretaceous.

Regional Jurassic geologic framework of Alabama coastal waters area and adjacent Federal waters area

Abstract To date, numerous Jurassic hydrocarbon fields and pools have been discovered in the Cotton Valley Group, Haynesville Formation, Smackover Formation and Norphlet Formation in the tri-state area of Mississippi, Alabama and Florida, and in Alabama State coastal waters and adjacent Federal waters area. Petroleum traps are basement highs, salt anticlines, faulted salt anticlines and extensional faults associated with salt movement. Reservoirs include continental and marine sandstones, limestones and dolostones. Hydrocarbon types are oil, condensate and natural gas. The onshore stratigraphic and structural information can be used to establish a regional geologic framework for the Jurassic for the State coastal waters and adjacent Federal waters areas. Evaluation of the geologic information along with the hydrocarbon data from the tri-state area indicates that at least three Jurassic hydrocarbon trends (oil, oil and gas condensate, and deep natural gas) can be identified onshore. These onshore hydrocarbon trends can be projected into the Mobile area in the Central Gulf of Mexico and into the Pensacola, Destin Dome and Apalachicola areas in the Eastern Gulf of Mexico. Substantial reserves of natural gas are expected to be present in Alabama State waters and the northern portion of the Mobile area. Significant accumulations of oil and gas condensate may be encountered in the Pensacola, Destin Dome, and Apalachicola areas.

Environments of Deposition and Petroleum Geology of Tuscaloosa Group (Upper Cretaceous), South Carlton and Pollard Fields, Southwestern Alabama

In southwestern Alabama, the lower Tuscaloosa Group (Upper Cretaceous) consists of two informally defined units, the Massive and Pilot sand intervals. The Massive sand interval accumulated principally as sands in a wave-dominated, high-destructive delta system. These sandstones are structureless, well sorted, micaceous, locally fossiliferous, calcareous, glauconitic, fine grained, and quartz rich, containing angular to subangular quartz grains. The Massive sand interval unconformably overlies fluvial-deltaic sediments of Lower Cretaceous strata. The Pilot sand interval, which overlies the Massive sand interval, accumulated as shelf sands and clays during a marine transgression. The sandstones are well sorted, micaceous, fossiliferous, calcareous, glauconitic, very fine to fine grained, and quartz rich, containing sub-angular to subrounded quartz grains. The sandstones appear massive but may be structureless as a result of extensive bioturbation. Marine bivalves, such as inoceramids, are present in the sandstones and claystones. The Pilot sand interval is overlain by a marine claystone (Marine shale) containing a diverse faunal assemblage of macroinvertebrates, including ammonites, inoceramids and other bivalves, and a rich microfossil assemblage of planktonic foraminifera and calcareous nannofossils. The Marine shale accumulated in an open-marine shelf environment. Petroleum traps in the Tuscaloosa are structural traps involving salt anticlines (South Carlton field) and extensional fault traps associated with salt movement (Pollard field). Reservoir-grade porosity occurs in the Massive and Pilot sandstone units as primary intergranular porosity. Although Tuscaloosa marine claystones contain significant amounts of organic carbon, these rocks are thermally too immature to be the petroleum source rocks for the Tuscaloosa crude oils in South Carlton and Pollard fields.

Geologic Framework of Norphlet and Pre-norphlet Strata of the Onshore and Offshore Eastern Gulf of Mexico Area

ABSTRACT Hydrocarbon accumulations have been discovered in the Jurassic Norphlet Formation in the onshore and offshore eastern Gulf of Mexico area. An understanding of the regional geologic framework of the Norphlet and pre-Norphlet stratigraphic succession in the study area is crucial to successful exploration for and development of Norphlet hydrocarbon reservoirs in the eastern Gulf region. These strata include Jurassic sedimentary rocks and pre-Jurassic sedimentary and crystalline rocks. Of these strata, only the Norphlet Formation has produced economic quantities of hydrocarbons from reservoirs which include eolian dune, interdune, wadi, and marine sandstones. However, the pre-Norphlet geology and paleotopography of the area controlled, to a large degree, Norphlet depositional patterns and subsequent structural development. Especially important were the locations of pre-Jurassic paleohighs and the distribution and thickness patterns of the underlying Jurassic Louann Salt. Norphlet hydrocarbon traps are generally associated with structures that have resulted from halokinesis of the Louann. Traps include salt anticlines, faulted salt anticlines, and extensional faults associated with salt movement. In addition to these salt-related structural traps, traps resulting from pre-salt basement paleotopography may exist in the study area. These traps might include Norphlet structural highs associated with preexisting basement highs and Norphlet stratigraphic terminations along the flanks of basement highs. Where Norphlet reservoir facies are present, the key factor controlling hydrocarbon accumulation potential is structural setting. In the Mississippi-Alabama-Florida (MAFLA) region that is underlain by the Norphlet Formation, four structural settings have been identified. Types A and B structural settings are characterized by Norphlet sediments overlying basement or thin salt; no Norphlet fields have been established in these settings. Types C and D structural settings are characterized by structures related to movement of thick Louann Salt; all Norphlet fields established in the MAFLA region occur in these settings. Four geographic regions have been defined in the study area for the purpose of characterizing Norphlet petroleum potential. Region 1 has excellent potential for future Norphlet discoveries, Region 2 has low to moderate potential, and Regions 3 and 4 have very little to no potential.

Depositional and Diagenetic History and Petroleum Geology of the Jurassic Norphlet Formation of the Alabama Coastal Waters Area and Adjacent Federal Waters Area

The discovery of deep (20,000 ft) gas reservoirs in eolian sandstone of the Upper Jurassic Norphlet Formation in Mobile Bay and offshore Alabama in the late 1970s represents one of the most significant hydrocarbon discoveries in the nation during the past several decades. Estimated original proved gas from Norphlet reservoirs in the Alabama coastal waters and adjacent federal waters is 7.462 trillion ft3 (Tcf) (75% recovery factor). Fifteen fields have been established in the offshore Alabama area. Norphlet sediment was deposited in an arid environment in alluvial fans, alluvial plains, and wadis in updip areas. In downdip areas, the Norphlet was deposited in a broad desert plain, with erg development in some areas. Marine transgression, near the end of Norphlet deposition, resulted in reworking of the upper part of the Norphlet Formation. Norphlet reservoir sandstone is arkose and subarkose, consisting of a simple assemblage of three minerals, quartz, albite, and K-feldspar. The present framework grain a...

Integrated Geological, Geophysical, and Geochemical Interpretation of Upper Jurassic Petroleum Trends in the Eastern Gulf of Mexico

ABSTRACT The petroleum potential of the Upper Jurassic strata in the Eastern Gulf of Mexico region is excellent. At least three Upper Jurassic petroleum trends can be delineated in the region. An oil trend can be identified onshore in the area north of the regional peripheral fault trend and is interpreted to extend offshore into the area north of the Destin anticline in the Eastern Gulf of Mexico. An oil and gas-condensate trend can be defined onshore between the regional peripheral fault trend and the Wiggins arch. This trend is projected to extend offshore into the area of the Destin anticline. A deep natural gas trend can be delineated onshore south of the Wiggins arch and extends offshore into the Mississippi-Alabama shelf area. These trends are recognized by hydrocarbon types, basinal position, and relationship to regional structural features. The main petroleum source rocks for the Upper Jurassic hydrocarbons are Smackover carbonate mudstones.

Upper Jurassic Smackover Oil Plays in Alabama, Mississippi and the Florida Panhandle

ABSTRACT Five Smackover (Upper Jurassic, Oxfordian) oil plays can be delineated in the eastern Gulf Coastal Plain. These include the basement ridge play, the regional peripheral fault trend play, the Mississippi Interior Salt basin play, the Mobile graben fault system play, and the Wiggins arch complex play. Plays are recognized by basinal position, relationships to regional structural features, and characteristic petroleum traps. Within two plays, subplays can be distinguished based on oil gravities and reservoir characteristics. Reservoirs are distinguished primarily by depositional setting and diagenetic overprint. The basement ridge play is updip of the regional peripheral fault trend where the Jurassic Louann Salt is thin or absent; structures in this trend formed on pre-Jurassic basement rocks. The basement ridge play is characterized by structural and combination traps. Reservoirs in the Choctaw ridge complex subplay are peritidal, partially to completely dolomitized, oolitic, peloidal, and oncoidal grainstone. Reservoirs of the Conecuh and Pensacola-Decatur ridge complexes subplay are subtidal to supratidal oolitic, oncoidal, intraclastic, and peloidal dolograinstone and dolopackstone, fenestral dolostone, quartz sandstone, and algal doloboundstone. The regional peripheral fault trend play is basinward of the updip limit of the Louann Salt and is typified by salt related structural features. These structural features occur in association with the Pickens, Gilbertown, West Bend, Pollard, and Foshee fault systems and are generally parallel to the basin margin. The regional peripheral fault trend play is exemplified by salt-related structural and combination traps. Reservoirs of the Pickens, Gilbertown, and West Bend fault systems subplay are peritidal, nondolomitic to completely dolomitized, oolitic, oncoidal, and peloidal grainstone. Reservoirs of the Pollard and Foshee fault systems subplay are subtidal to supratidal, partially to completely dolomitized, peloidal grainstone to wackestone, and dolomitized algal boundstone. The Mississippi interior salt basin play is downdip from the Pickens and Gilbertown fault systems and is characterized by structural and combination traps associated with salt tectonism in this basin. Reservoirs are peritidal, nondolomitic to completely dolomitized, oolitic and peloidal grainstone and packstone. The Mobile graben fault system play is located along the eastern limit of the Mississippi interior salt basin and is typified by salt-induced structural and combination traps and Smackover peritidal peloidal and oolitic dolograinstone to dolowackestone and dolostone reservoirs. The Wiggins arch complex play is in a downdip basinal position and is characterized by structural and combination-petroleum traps associated with stratigraphic thinning and salt flow. The traps occur along the flanks of pre-Mesozoic paleohighs associated with this complex. Reservoirs are subtidal to supratidal peloidal, oolitic and oncoidal dolograinstone and dolopackstone, thrombolitic dolostone, and crystalline dolostone.

Natural Gas Plays in Jurassic Reservoirs of Southwestern Alabama and the Florida Panhandle Area

ABSTRACT Three Jurassic natural gas trends can be delineated in southwestern Alabama and the Florida panhandle area. These include a deep natural gas trend, a natural gas and condensate trend, and an oil and associated natural gas trend. Trends are recognized by hydrocarbon types, basinal positions, and relationships to regional structural features. Within these natural gas trends, eight distinct natural gas plays can be identified. Plays are recognized by characteristic hydrocarbon traps and reservoirs. The deep natural gas trend includes the Mobile Bay area play that is characterized by structural hydrocarbon traps associated with salt tectonism and Norphlet sandstone reservoirs at depths exceeding 20,000 feet. The natural gas and condensate trend includes the Mississippi interior salt basin play, the Mobile graben play, the Wiggins arch complex play, and the Pollard fault system play. The Mississippi interior salt basin play is typified by salt-related structural and combination hydrocarbon traps and Smackover dolomitized oolitic, oncolitic, and peloidal grainstone and packstone reservoirs at depths of approximately 16,000 feet. The Mobile graben play is exemplified by salt-induced structural hydrocarbon traps and Smackover dolostone and Norphlet sandstone reservoirs at depths ranging from 12,400 to 18,400 feet. The Wiggins arch complex play is characterized by structural and combination hydrocarbon traps associated with stratigraphic pinch-outs and salt flow. These traps are salt-related and occur along the flanks of paleohighs associated with the Wiggins arch complex. Smackover dolostone reservoirs at depths ranging from 16,100 to 18,400 feet are typical of this play. The Pollard fault system play is typified by salt-induced structural hydrocarbon traps and reservoirs at depths of approximately 15,000 feet. These reservoirs are Smackover dolomitized oolitic and peloidal grainstones and packstones and Norphlet sandstones. The oil and associated natural gas trend includes the Gilbertown and West Bend fault systems play, the Foshee fault system play, and the basement ridge play. The Gilbertown and West Bend fault systems play is exemplified by salt-related structural or combination traps and Smackover dolomitized oolitic, oncolitic, and peloidal grainstone and packstone reservoirs and Norphlet sandstone reservoirs at depths ranging from 11,000 to 14,000 feet. The Foshee fault system play is characterized by structural and combination hydrocarbon traps related to salt movement and Smackover dolomitized peloidal grainstone and packstone and Norphlet sandstone reservoirs at depths of approximately 15,000 feet. The basement ridge play, which is typified by structural and combination traps associated with the Conecuh and Pensacola-Decatur ridge complexes and Smackover oolitic and peloidal grainstone and packstone and algal boundstone and Haynesville sandstone reservoirs at depths ranging from 11,800 to 15,500 feet, has potential for significant undiscovered natural gas.

Upper Jurassic Norphlet Formation--New Frontier for Hydrocarbon Prospecting in the Central and Eastern Gulf of Mexico Regions: ABSTRACT

Since the discovery of oil in 1967 from the Smackover Formation at Toxey field, Choctaw County, Alabama, and of condensate in 1968 from the Norphlet Formation at Flomaton field, Escambia County, Alabama, the Upper Jurassic has become the primary exploration target in southwestern Alabama. Following those initial discoveries, 39 Upper Jurassic fields have been established in Alabama, but only in 4 of these has the Norphlet produced hydrocarbons. The discovery of productive Norphlet gas sandstones in 1979 at the Lower Mobile Bay-Mary Ann field, offshore Alabama, has demonstrated the potential of the Norphlet in the central and eastern Gulf of Mexico regions. All 4 wells drilled to test the Norphlet in Mobile Bay have been successful gas wells, and have tested between 10.5 a d 19.4 mmcf per day. Although drilling is to depths exceeding 20,000 ft (6,100 m) subsea, the projected gas reserves justify continued exploration. Norphlet petroleum traps in the region are principally combination traps involving favorable stratigraphy and salt anticlines (Copeland field), extensional fault traps associated with salt movement (Flomaton field), and faulted salt anticlines (Hatters Pond and Lower Mobile Bay-Mary Ann fields). Reservoir rocks include marine, dune, and fluvial sandstone lithofacies. Sandstone porosity involves both primary intergranular and secondary dissolution and fracture. Smackover algal carbonate mudstone is probably the source for much of the Norphlet hydrocarbon, but downdip Norphlet marine shales may also be source rocks. The central and eastern Gulf of Mexico regions should continue to be excellent areas to explore for hydrocarbons in the years ahead. Successful Norphlet petroleum prospecting in the area has involved the identification of favorable sandstone lithofacies and structural hydrocarbon traps by using geologic and geophysical methods. Future Norphlet discoveries will require the delineation of stratigraphic and structural/stratigraphic combination hydrocarbon traps using seismic-stratigraphic techniques. End_of_Article - Last_Page 502------------

Desert Environments and Petroleum Geology of the Norphlet Formation, Hatter’s Pond Field, Alabama

Reservoirs of the Norphlet Formation provide good examples of the varied influences of depositional and diagenetic controls on reservoir distribution and quality. Norphlet sandstones are representative of a variety of desert and near-desert depositional settings, and show a considerable range in reservoir quality. The degree to which deep burial of the Norphlet has overprinted and modified the depositional controls of reservoir quality is varied, as seen in this chapter and the two which follow. The Norphlet reservoir in the Hatter’s Pond Field provides an opportunity to compare and contrast the reservoir quality of several desert and near-desert sequences, including wadi, playa dune, and nearshore-marine lithofacies. Reservoir quality varies greatly, and the most productive lithofacies are dune and shoreface sandstones.