Norphlet Formation Research Articles

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

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.

Seismic expression of structural style in Norphlet formation, offshore Alabama

During the past several years, the Jurassic Norphlet formation in offshore Alabama has been the focus of active exploration and development operations. Since the 1979 discovery of deep gas [greater than 6096 m (20 000 ft)] in Norphlet sandstones which contain estimated reserves of several trillion cubic feet, six Norphlet fields have been established in Alabama state waters and an additional six fields have been established in Federal Outer Continental Shelf (OCS) waters in offshore Alabama. We describe, using seismic data, the structural style associated with the Norphlet formation in offshore Alabama. More than 563 line‐kilometers (350 line‐miles) of multifold common‐depth‐point (CDP) seismic reflection data in Mobile Bay and offshore Alabama have been analyzed, interpreted, and mapped. The Lower Mobile Bay‐Mary Ann natural gas field provides an excellent seismic case study for the structural style in the deep Norphlet play. The field may be used as a geophysical exploration model for other Jurassic structures in offshore Alabama and the central and eastern Gulf of Mexico. Interpretation of the seismic data and maps indicates that Norphlet structures in offshore Alabama are predominantly east‐west trending, low‐relief, broad, elongate anticlines. The Lower Mobile Bay fault trend associated with the anticlines consists of pull‐apart, listric, normal faults characteristic of salt‐detachment structures. Many of these faults exhibit small‐scale growth. Salt thickness ostensibly increases from Mobile Bay to offshore Alabama and is exemplified by the development of a sequence of various structures typically associated with basinward increase of salt. Offshore Alabama structures may be classified as early horizontal phase or pillow‐stage features. Strata above the Haynesville seismic marker appear to be relatively flat, indicating early salt movement in the area. Small downbends associated with salt withdrawal exhibit thickening in the Haynesville‐Smack‐over section and are further complicated by normal faulting. The preponderance of the data suggests that the structures containing the large gas accumulations in the Norphlet formation in offshore Alabama are the result of salt tectonism.

Diagenesis of Fluvial Sands in Norphlet Formation (Upper Jurassic), Escambia County, Alabama: ABSTRACT

The Upper Jurassic Norphlet Formation is an important hydrocarbon reservoir in Baldwin and Mobile Counties and offshore in Mobile Bay, Alabama. The formation is not productive in the Little Escambia Creek field, Escambia County, but underlies the productive Smackover Formation at a depth of approximately 15,500 ft (4725 m). The Norphlet sandstones examined in cores from two drill holes are largely fluvial in origin and consist of moderately to well-sorted, very fine to coarse-grained feldspathic sandstones extensively altered by a complex sequence of diagenetic reactions. Visible evidence of chemical and mechanical compaction is relatively minor in the sandstones. Paucity of compaction suggests that extensive early cementation by anhydrite and/or calcite reduced compaction; these cements were subsequently removed by migrating fluids. Porosity, both intergranular and intragranular, is generally well developed. Intergranular pores are due primarily to partial to complete dissolution of cements and mineral grains, especially feldspar. Intragranular pores are largely the result of partial leaching of rock fragments and of microporosity formed by precipitation of clay minerals in earlier dissolution pores.

Geochemical Relationships of Petroleum in Mesozoic Reservoirs to Carbonate Source Rocks of Jurassic Smackover Formation, Southwestern Alabama

Algal carbonate mudstones of the Jurassic Smackover Formation are the main source rocks for oil and condensate in Mesozoic reservoir rocks in southwestern Alabama. This interpretation is based on geochemical analyses of oils, condensates, and organic matter in selected samples of shale (Norphlet Formation, Haynesville Formation, Trinity Group, Tuscaloosa Group) and carbonate (Smackover Formation) rocks. Potential and probable oil source rocks are present in the Tuscaloosa Group and Smackover Formation, respectively. Extractable organic matter from Smackover carbonates has molecular and isotopic similarities to Jurassic oil. Although the Jurassic oils and condensates in southwestern Alabama have genetic similarities, they show significant compositional variations due to differences in thermal maturity and organic facies/lithofacies. Organic facies reflect different depositional conditions for source rocks in the various basins. The Mississippi Interior Salt basin was characterized by more continuous marine to hypersaline conditions, whereas the Manila and Conecuh embayments periodically had lower salinity and greater input of clastic debris and terrestrial organic matter. Petroleum and organic matter in Jurassic rocks of southwestern Alabama show a range of thermal transformations. The gas content of hydrocarbons in reservoirs increases with increasing depth and temperature. In some reservoirs where the temperature is above 266°F (130°C), gas-condensate is enriched in isotopically heavy sulfur, apparently derived from thermochemical reduction of Jurassic evaporite sulfate. This process also results in increased H2S and CO2 in the gas, and depletion of saturated hydrocarbons in the condensate liquids. Thermochemical sulfate reduction probably depends on the mineralogic composition of the reservoir rock as well as temperature, because some deep (18,000 ft or 5.5 km) and hot (320°F or 160°C) Smackover and Norphlet reservoirs contain low-sulfur petroleum.

Diagenesis and Preservation of Porosity in Norphlet Formation (Upper Jurassic), Southern Alabama

Sandstones of the Norphlet Formation (Upper Jurassic) in the vicinity of Lower Mobile Bay, Alabama, have porosities greater than 20% and permeabilities up to about 1 darcy at depths of more than 20,000 ft (6,096 m). Typically, pre-Tertiary sandstones buried to such depths have approximately 6% (±2%) porosity; thus, deep Norphlet sandstones contain up to 14% excess porosity. This porosity is largely intergranular and appears to be preserved primary porosity. When the diagenetic scenario for the Norphlet is reconstructed in a time-temperature framework, it is apparent that porosity preservation is not the result of any single diagenetic event, but is due to a continuous series of diagenetic conditions that overlapped in time. The most important of these circumstances were the following. (1) The lack of pervasive early calcite or anhydrite cements found in the large eolian dunes (10-300 ft or 3-91 m high) that comprise the best Norphlet reservoirs. This lack of cement may have set the stage for subsequent events by keeping open pathways through which fluids were later able to efficiently contact the sandstone. (2) Early grain-coating clay/iron oxide rims reacted to form chlorite in the 176°-248°F (80°-120°C) thermal wind w. The grain-rimming chlorite may have inhibited subsequent quartz cementation. Up to 10.5% porosity may be due to the porosity preserving effect of chlorite. (3) Migration of hydrocarbons and development of geopressures, beginning at temperatures as low as 230°F (110°C), retarded further cementation. Up to 4.5% porosity may be due to the combined effects of hydrocarbons and geopressures. (4) A series of CO2-generating reactions occurred, including decarboxylation of organic acids, thermal cracking of liquid hydrocarbons, and thermochemical sulfate reduction. As a result of these reactions, late carbonate cements were not abundant. Thermochemical sulfate reduction (275°-356°+F or 135°-180°+C) has been of particular importance in the deep Norphlet. Reaction of hydrocarbons with anhydrite has resulted in the local removal of nodular anhydrite and has also affected gas quality (i.e., H2S content). The preserved porosity in Norphlet sandstones is the result of a combination of circumstances. The fact that these conditions overlapped in time-temperature space may be as important as any single factor.

Model for Isopaching Jurassic-Age Norphlet Formation in Mobile Bay, Alabama Area: ABSTRACT

Model for Isopaching Jurassic-Age Norphlet Formation in Mobile Bay, Alabama Area: ABSTRACT

Diagenesis and Porosity Evolution, Norphlet Formation in Mobile Bay, Alabama: ABSTRACT

Diagenesis and Porosity Evolution, Norphlet Formation in Mobile Bay, Alabama: ABSTRACT

Diagenesis of Upper Jurassic Norphlet Formation, Mobile and Baldwin Counties and Offshore Alabama: ABSTRACT

ABSTRACT The Upper Jurassic Norphlet Formation is an important deep gas reservoir in Mobile and Baldwin Counties and the adjacent Alabama state waters. The reservoir is a well-sorted, fine-grained subarkose to arkose deposited in eolian dune, interdune, wadi, and beach-shoreface environments. Arid depositional conditions and a subsequent marine transgression left an early diagenetic imprint on the sandstone. Near-surface cementation by hematite, quartz, k-feldspar, carbonate, and sulfate minerals occurred concurrently with mechanical compaction. With continued burial, illite and chlorite grain coatings and additional carbonate cements were precipitated. Thermomaturation of organic matter in the overlying Smackover produced carbonic and carboxylic acids and hydrogen sulfide. The introduction of these components into the Norphlet resulted in widespread dissolution of framework grains, grain replacements, and early cements. Pressure solution, saturation of the acid fluids, and invasion of brines from the underlying Louann Salt resulted in the late-stage precipitation of quartz, K-feldspar, anhydrite, and carbonate cements. Porosity in the Norphlet is a mixture of primary intergranular porosity and secondary porosity produced through dissolution of cements, detrital grains, and grain replacements prior to hydrocarbon emplacement. Porosity ranges from zero to 25 percent and averages around 10 percent. Permeabilities range from 0.1 millidarcy to almost 100 millidarcies but are typically less than 1.0 millidarcy. Porosity and permeability vary within the study area as a consequence of geographic differences in diagenetic history and authigenic mineralogy. The best reservoirs occur in northern Baldwin County and in the offshore area.

Petrology and Provenance of Norphlet Formation, Florida Panhandle: ABSTRACT

Petrology and Provenance of Norphlet Formation, Florida Panhandle: ABSTRACT

Recoverable Natural Gas Reserves from Jurassic Norphlet Formation, Alabama Coastal Waters: ABSTRACT

ABSTRACT To date, eleven Norphlet gas fields have been established in offshore Alabama. These fields are part of a deep Jurassic gas trend that extends across southern Mississippi and Alabama into the Gulf of Mexico. Recoverable reserves of 4.9 to 8.1 trillion cubic feet of gas are estimated for the Norphlet formation in Alabama's coastal waters. Proven reserves are estimated to be 3.7 to 4.6 trillion cubic feet of gas, and potential reserves are estimated to be 1.2 to 3.5 trillion cubic feet of gas. The natural gas is trapped in a series of generally east-west trending salt anticlines. The mechanism of structure formation appears to be salt flowage that has formed broad, low-relief anticlines, most of which are faulted and many of which are related to small-scale growth faults. Salt movement is the critical factor in the formation of these petroleum traps. The primary Norphlet reservoir lithofacies are eolian dune and interdune sandstones that range in thickness from 140 to over 600 feet in Alabama's coastal waters. Gas pay can exceed 280 feet in thickness. Porosity is principally secondary developed as a result of decementation and grain dissolution. Jurassic Smackover algal carbonate mudstones were the main source for the Norphlet hydrocarbons. The seal for the gas is the nonpermeable upper portion of the Norphlet Formation. The overlying lower Smackover carbonates are also nonpermeable and may serve as pad of the seal.

Norphlet Formation (Upper Jurassic) Sand Erg: Depositional Model for Northeastern De Soto Salt Basin, Eastern Gulf of Mexico: ABSTRACT

Available well control, seismic reflection geometries, and seismic modeling suggest the interpretation of a Norphlet Formation (Upper Jurassic) sand erg in the northeastern De Soto salt basin. Ranging in thickness from less than 100 ft to nearly 1000 ft, the Norphlet erg encompasses an area of approximately 700 mi/sup 2/. Separated from the major gas accumulation in the Norphlet in the Mobile Bay area by the offshore extension of the Pensacola arch, the Norphlet erg appears to be oriented transverse to the axis of the De Soto salt basin. Seismic signatures for the Smackover carbonate, Norphlet sand, and Louann Salt intervals are investigated using synthetic seismograms generated from six wells in the eastern Gulf of Mexico. General characteristics about the reflection coefficients from the major units in the interval are noted. The reflection coefficient information and synthetic seismograms are used to interpret seismic data on a regional basis. Two-dimensional, vertical-incidence, ray-trace modeling of the seismic data is done to aid the interpretation on a detailed basis. Interpreted Norphlet sandstone thicknesses and Louann Salt structures are combined to support the Norphlet Formation sand erg hypothesis.

Reservoir Quality, Sediment Source, and Regional Aspects of Norphlet Formation, South State Line Field, Greene County, Mississippi: ABSTRACT

South State Line field, discovered in 1970, is centrally located in the productive Jurassic Norphlet trend of the eastern Gulf Coast. The Norphlet Formation at South State Line has produced gas and condensate from normally pressured eolian sandstones at depths of more than 17,900 ft (5455 m). The 600-ft- (183-m) thick Norphlet Formation is composed of 100% sandstone and consists of two reservoir types: a poorer quality upper sandstone having low permeability (0.6 md) and a good-quality lower sandstone with better permeability (15.5 md). The upper sandstone exhibits tighter compaction of framework grains and more cement than the lower sandstone. Significantly, the upper sandstone contains authigenic illite (which promotes pressure solution), whereas the lower sandstone contains authigenic chlorite (which inhibits cementation and possibly pressure solution). On a regional scale, illite is the principal diagenetic clay mineral in the western area of the Norphlet trend (Mississippi to Texas), whereas chlorite is the principal diagenetic clay mineral in the east (Alabama to Florida). Not surprisingly, reservoir quality is poorer in the western portion of the trend. A comparison of framework grains in the upper and lower sandstones shows no significant compositional differences. Both are mature arkosic sandstones with a transitional-continental source (easternmore » Appalachians). No evidence was seen of a quartz-rich Ouachita or cratonic source. Volcanic and plutonic rock fragments are slightly more abundant in the lower sandstone, possibly reflecting a shifting of compositional terranes within a single source area along the eastern side of the Appalachians. The lower Norphlet sandstone may have been derived from Triassic volcanics, whereas the upper sandstone may have been derived from a more metamorphic source.« less

Diagenesis of Eolian and Fluvial Feldspathic Sandstones, Norphlet Formation (Upper Jurassic), Rankin County, Mississippi, and Mobile County, Alabama

Norphlet sandstones in seven cores from Mississippi and Alabama are arkoses and subarkoses deposited in eolian-dune, interdune, and fluvial environments. Similar to the deeply buried (> 5 km) Tertiary feldspathic sandstones of the Gulf basin, all detrital plagioclase that survived dissolution has been albitized. However, some K-feldspar, instead of dissolving, was stabilized by K+-rich brines derived from adjacent evaporites. This K-feldspar then developed extensive overgrowths. Fluvial red sandstone lost all initial porosity by the introduction of preburial pedogenic calcite and compaction. Initial porosity of eolian sands was reduced by compaction to an average of 29%; and later by cementation by quartz, carbonates, anhydrite, halite, K-feldspar, and illite. Quartz and anhydrite cements precipitated between 90° and 100°C (approximately 2.3 km deep), carbonates and halite cements formed below 120°C (< 3 km), and late-stage illite cement formed between 130° and 150°C (4-5 km deep). Cements are patchy, and some, especially quartz and anhydrite, are texture-selective, being more abundant in coarser laminae. Secondary porosity, which makes up approximately half the porosity in thin sections, formed by dissolution of detrital grains (f ldspar, rock fragments) and cements (anhydrite, carbonate, halite). Reservoir bitumen records an early phase of oil entrapment. Reservoir quality is influenced by the abundance of reservoir bitumen and thread-like illite, both of which bridge pores. The radiometric age of illite (approximately 55 Ma) probably reflects its cementation age, but may also record a later recrystallization event. Depleted oxygen and carbon isotopic values for ferroan dolomite reflect the progressive replacement of earlier, more enriched carbonate phases by higher temperature phases. Isotopic data suggest that during the first 30 to 40 m.y. of burial, subsurface diagenesis of the Norphlet Formation was dominated by deep-circulating, hot, meteoric water. This phenomenon may be characteristic of the early diagene ic history of rifted basins.

Depositional Environments and Petroleum Geology of Jurassic Eolian Deposits (Norphlet Formation), Eastern Gulf of Mexico Area: ABSTRACT

Jurassic Norphlet sediments in the eastern Gulf of Mexico area accumulated under arid climatic conditions. The accumulation of thick Jurassic salt deposits, anhydrites, and red beds in association with Norphlet sandstones indicates that arid climatic conditions were prevalent during Norphlet deposition. Usually an association of salt deposits, anhydrites, and red beds is characteristic of arid climatic conditions, and eolian sands can be expected to accumulate under such depositional conditions. The Appalachian Mountains of the eastern United States extended into southwestern Alabama and provided a barrier for air and water circulation during the deposition of the Norphlet Formation. These mountains produced the topographic conditions that contributed to the arid climate. In the region, Appalachian structural features are recognized as basement ridges and arches, such as the Conecuh and Pensacola ridges and associated Wiggins arch. These paleohighs affected Norphlet sedimentation and acted as local sediment sources. Norphlet paleogeography in the eastern Gulf coastal plain 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 began as a result of basin subsidence accompanied by erosion of the southern Appalachians. Norphlet conglomerates were deposited in coalescing alluvial fans near 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 during the late phase of deposition of the Norphlet Formation resulted in the reworking of previously deposited Norphlet sediments. To date, 35 Norphlet oil and gas fields have been established in the region. Petroleum traps discovered are principally structural traps involving salt anticlines, faulted salt anticlines, and extensional fault traps associated with salt movement. Although basement highs also have potential as petroleum traps in the area, salt movement is the critical factor in forming a petroleum trap. Numerous Norphlet fields are located along the regional peripheral fault trend, particularly in association with the Pollard-Foshee fault system in southern Alabama and the Florida panhandle. Other onshore Norphlet petroleum traps include salt anticlines, such as Copeland, and salt grabens, such as the Mobile graben. In Mississippi, several Norphlet fields are located near the Jackson dome, a Cretaceou igneous intrusion. The Norphlet fields discovered in offshore Alabama are along the Lower Mobile Bay fault trend. The petroleum traps in the offshore area include a series of generally east-west-trending salt anticlines. Reservoir rocks consist primarily of quartz-rich sandstones of eolian, wadi, and marine origin. The average composition of these quartz-rich sandstones is 72.5% quartz, 15.0% feldspar (plagioclase, microcline, and orthoclase), 4.4% rock fragments (chert, shale, phyllite, schist, and quartzite), 3.8% cement (carbonate, quartz, and anhydrite), 3.2% authigenic clay, and 1.1% accessory minerals. Porosity includes primary intergranular and secondary intergranular, and intragranular developed as a result of decementation and grain dissolution. Porosity in Norphlet reservoirs can exceed 25%. The primary source of hydrocarbons in the Norphlet reservoirs is Smackover carbonate mudstones. Norphlet shale samples analyzed were found to be low in total organic carbon (0.1-0.2%). Smackover carbonate mudstones are locally rich in algal and amorphous kerogen. The geochemical and carbon isotopic composition of Norphlet crude oils compares favorably with the composition of Smackover crude oils and Smackover carbonate mudstones. End_of_Article - Last_Page 1441------------

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.

Upper Jurassic Norphlet Eolian Dune, Wadi, and Marine Petroleum Reservoirs, Central and Eastern Gulf of Mexico Regions: ABSTRACT

The Norphlet Formation (Upper Jurassic) of the central and eastern Gulf of Mexico regions accumulated under arid climatic conditions. Norphlet paleogeography in southwestern and offshore Alabama and the Florida Panhandle was dominated by a broad desert plain rimmed to the north and east by the Appalachian Mountains and to the south by a developing shallow sea. The desert plain extended westward into eastern and central Mississippi. Quartzose sandstones were deposited as dune and interdune sediments. The source of the sand was adjacent and updip alluvial-fan, plain, and wadi deposits. Wadi and playa-lake sediments also accumulated in the interdune areas. A marine transgression was initiated during upper Norphlet deposition resulting in the reworking of previously deposited sediments. Petroleum reservoir rocks consist primarily of quartzose sandstones that are eolian dune, wadi, and marine in origin. The high-angle (up to 30°) cross-bedded eolian sandstones are moderately well-sorted to well-sorted End_Page 282------------------------------ subarkoses having subrounded to rounded quartz grains. The dune and interdune sandstones are interbedded with wadi and playa-lake deposits having wavy discontinuous laminae. These water-deposited sandstones are not as texturally mature as the dune sandstones. The upper part of the Norphlet includes massively bedded to horizontal laminated marine sandstones. Porosity is principally secondary dissolution with some intergranular porosity. The secondary porosity is a result of decementation of anhydrite and/or calcite and by grain dissolution. Porosity in the marine sandstones is reduced through calcite cementation in downdip areas. The Permian eolian dune and wadi sandstone reservoirs in the Viking field, North Sea, can be used as analogs for anticipating reservoir performance for the No phlet sandstones. End_of_Article - Last_Page 283------------

Upper Jurassic Norphlet Hydrocarbon Potential Along Regional Peripheral Fault Trend in Mississippi, Alabama, and the Florida Panhandle: ABSTRACT

ABSTRACT Recent Upper Jurassic Norphlet oil discoveries associated with the West Bend fault system in Clarke County, Alabama, and the Foshee fault system in Escambia County, Alabama, have renewed interest in exploring for hydrocarbons along the regional peripheral fault trend in Mississippi, Alabama, and the Florida panhandle. The recently discovered Chavers Creek and Sizemore Creek oil fields and the Strickland 10-4 No. 2 oil discovery in Escambia County, Alabama, are upthrown to the Foshee fault system. The trap at Chavers Creek field is a faulted salt anticline, and the trap at Sizemore Creek field is an elongate salt anticline. The reservoir at Chavers Creek and Sizemore Creek oil fields includes eolian and wadi sandstones of the Norphlet Formation. Porosity is estimated to be 11 to 22%, and permeability is estimated to be 14 to 47 millidarcies. The oil in Chavers Creek field has an API gravity of 42.7°, and the oil in Sizemore Creek field has an API gravity of 59.9°. The 1985 Womack Hill Field Unit No. 14-5 oil discovery in Clarke County is upthrown to the West Bend fault system. The Norphlet oil discoveries in Clarke and Escambia Counties, Alabama, and the distribution of established productive Norphlet hydrocarbon fields in Mississippi, Alabama, and the Florida panhandle demonstrate the petroleum potential along the regional peripheral fault trend in central and eastern Mississippi, southwestern Alabama, and the Florida panhandle. The keys to successful prospecting for hydrocarbons along this fault trend are the delineation of faulted salt anticlines or salt anticlines, and the identification of associated reservoir grade eolian, wadi, and/or marine sandstones of the Norphlet Formation.

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 (Hatter's 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------------

Paleoenvironments and Hydrocarbon Potential of Upper Jurassic Norphlet Formation of Southwestern Alabama and Adjacent Coastal Water Area: ABSTRACT

Upper Jurassic Norphlet sediments in southwestern Alabama and the adjacent coastal water area accumulated under arid climatic conditions. The Appalachian Mountains of the eastern United States extended into southwestern Alabama, providing a barrier for air and water circulation during Norphlet deposition. These mountains not only contributed to the arid climate but also affected sedimentation. Norphlet paleogeography 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. Initiation of Norphlet sedimentation was a result of 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-bed lithofacies that accumulated in distal portions of alluvial fan and wadi systems. Quartzose sandstones (Denkman Member) were deposited as dune and interdune sediments on a broad desert plain. The source of the sand was the updip and adjacent alluvial fan, plain, and wadi deposits. Wadi and playa lake sediments probably also accumulated in the interdune areas. A marine transgression was initiated late in Denkman deposition, resulting in the reworking of previously deposited Norphlet sediments. Norphlet hydrocarbon potential in southwestern and offshore Alabama is excellent with four oil and gas fields already 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 of quartzose sandstones, which are principally eolian in origin. Porosity types include both intergranular and secondary dissolution. Smackover algal carbonate mudstones were probably the source for the Norphlet hydrocarbons. End_of_Article - Last_Page 1215------------

Application of Strontium Isotopes to Origin of Smackover Brines and Diagenetic Phases, Southern Arkansas: ABSTRACT

The abundance of the isotope 87Sr is variable in nature, as it is the radiogenic product of 87Rb decay. The relative amount of this Sr isotope that is dissolved in a brine, as expressed by the 87Sr/86Sr ratio, might be used as a tracer of the origin and subsequent history of the brine, including its diagenetic effects in petroleum reservoirs. Strontium isotopic analyses of 40 brines from oil fields in southern Arkansas have been conducted to investigate the sources of the dissolved Sr, the pathways of brine migration, and the relationship between the brines and diagenetic phases in the Jurassic upper Smackover Formation. The 87Sr/86Sr ratios of 33 brines from the upper Smackover lime-grainstone range from 0 7071 to 0.7101; seven brines from formations stratigraphically above the Smackover range from 0.7090 to 0.7112. Thus the Sr in these brines is variably more radiogenic than Jurassic sea water End_Page 553------------------------------ (~0.7070). The brines are from 15 oil fields within an area of approximately 2,000 mi2 (5,200 km2); the isotopic variability shows no geographic pattern in the study area. The variation in 87Sr/86Sr ratios of brines occurs to a lesser degree within individual oil fields. For example, over a distance of about 10 mi (16 km) at Walker Creek, the isotopic ratios of 11 Smackover brines range from 0.7080 in the east to 0.7086 in the west. The observation that Smackover brines are variably more radiogenic than Jurassic seawater is important because it indicates that a significant proportion of the Sr dissolved in these brines has been acquired from a source material that has not formed wholly by precipitation from Jurassic seawater. That is, some radiogenic Sr must have been added to the brines from a detrital source material. The nature and distribution pattern of the 87Sr/86Sr ratios indicate the acquisition of variable amounts of radiogenic Sr on a local basis. If the Smackover brines originated in the Louann Salt, with 87Sr/86Sr equivalent to that of Jurassic seawater, their present isotopic compositions may be the result of varying degrees of subsequent interaction with d trital sediments or they may have been produced by mixing in variable proportions with solutions containing more radiogenic Sr. Potential sources of the radiogenic Sr are the Norphlet Formation and the lower Smackover argillaceous lime-mudstone, both of which lie stratigraphically between the Louann salt and the upper Smackover, as well as the Bossier shale which interfingers with the upper Smackover in the North Louisiana salt basin. Anhydrites from the Werner and Buckner formations and from northern Louisiana salt domes, which constitute additional potential sources of brine Sr, yield 87Sr/86Sr ratios equivalent to those of Jurassic seawater. Diagenetic phases of the upper Smackover, such as post compaction calcspar cement and baroque dolomite, have 87Sr/86Sr ratios more radiogenic than Jurassic seawater, suggesting their subsurface precipitation in Sr isotopic equilibrium with Smackover brines. However, ooids and oncolites from the upper Smackover lime-grainstone yield 87Sr/86Sr ratios indicating isotopic equilibrium with Jurassic seawater. End_of_Article - Last_Page 554------------