Excellent Reservoir Properties Research Articles

Geology of Fulmar Oil Field, United Kingdom Sector, Central North Sea: ABSTRACT

The Fulmar field is situated within the United Kingdom sector of the central North Sea, 170 mi (270 km) southeast of Aberdeen, in water depths averaging 265 ft (81 m). The field was discovered in 1975 when Shell/Esso well 30/16-6 established the presence of an important oil play within shallow-marine sands of Late Jurassic age in the southwest Central graben of the North Sea basin. The well encountered an oil column of 668 ft (204 m) within apparently homogeneous sandstones displaying excellent reservoir properties. Commercial production was confirmed by an appraisal well, and 4 development wells were pre-drilled from a subsea template prior to platform production, which commenced in February 1982. The reservoir geology was consequently found to be more complicated than o iginally thought and has led to a diversity of depositional and structural models. To date, 23 development wells have been drilled. Current recoverable oil reserves are estimate at 427 million bbl with an oil gravity of 40° API. Fulmar field is operated by Shell U.K. Ltd. on behalf of the Shell/Esso North Sea Venture and the Fulmar Unit. End_of_Article - Last_Page 282------------

Hydrodynamic Control on an Oil Entrapment in Channel Sandstones of the Dakota Sandstone, South Cole Creek Field, Converse County, Wyoming

South Cole Creek field, located in the southwest Powder River Basin of Wyoming has produced 11 million barrels of oil from the Dakota Sandstone. Detailed mapping of rock and reservoir properties including sandstone isopachs, initial potentials, cumulative production, and porosity-permeability data, reveals the existence of channel sandstones with excellent reservoir properties which are surrounded by marine rocks of poorer reservoir properties. The areal extent of the accumulation is controlled by factors other than structure and stratigraphy, as water-bearing channel sandstones exist lateral to and up-dip of producing channel sandstones. By comparing the known accumulation to the theoretical model for fluid flow, it can be shown that hydrodynamics has played an important role in modifying the accumulation at South Cole Creek field.

Lower Cretaceous Viking Barrier Island, Southwestern Alberta, Canada: ABSTRACT

A subsurface study of cores and electric well logs from the lower Cretaceous (Albian) Viking reservoir sandstone near Calgary, Alberta, reveals its deposition as a regressive barrier island along the shores of the Haplophragmoides gigas sea. The barrier island trends northwest-southeast parallel to the paleostrandline for more than 120 km (75 mi) and attained a maximum thickness of more than 30 m (100 ft). Swales characterized by isopach thinning suggest that the island was probably breached by two tidal channels. Bentonite chronostratigraphy indicates that the barrier island prograded in a northeasterly and/or easterly direction for up to 24 km (15 mi). This seaward growth was briefly interrupted by an isostatic transgression. Thus, sandstone depositional pattern is of the imbricate type with younger units successively displaced seaward in the direction of progradation. The barrier-island facies sequence comprises eleven intergradational facies, i.e., ebb-tidal delta, marginal (spillover) channel, middle shoreface, marine shales, upper shoreface beach, dune, back-barrier mud flat, marshy lagoon and overwash, mixed tidal flat, tidal creek channel, and overbank. This sequence differs slightly from that of the Recent classic regressive Galveston Island, Texas, and the ancient Muddy barrier island, Montana, in the presence of an ebb-tidal delta and marine shelf shales beneath and above the middle shoreface facies, respectively. On this basis the South Carolina Recent barrier islands are considered closer modern analogs. The writer suggests that this sand body be explored further for oil and/or gas accumulations because of its excellent reservoir properties and the generally low well density. End_of_Article - Last_Page 448------------

Structural History and Oil Potential of Offshore Area from Cape Hatteras to Bahamas

The present Atlantic Coastal Plain and continental shelf were parts of the crystalline Appalachians in late Paleozoic time when North America was joined to the African continent, according to current interpretation of plate tectonics. In Early Triassic time this province was uplifted by subcrustal intrusion of hot mantle material which caused a series of rift valleys to develop with trends roughly parallel with the present continental rise. This was the site of a major rift system and the convection cell which later formed the Mid-Atlantic Ridge. This rift system connected the Mediterranean Sea with the newly opened Gulf of Mexico; these were areas of extensive evaporite deposition in Late Triassic and Early Jurassic times. Normal sea water entering during Smackover (Late Jurassic) deposition permitted the growth of great carbonate banks and reefs from the Cape Hatteras area southward to the Bahamas. Active separation of Africa and North America also moved the upwelling lavas of the Mid-Atlantic Ridge away from the coastlines. Cooling of the hot mantle material under the continental margin caused downward flexing of the crust toward the ocean to form a new miogeosyncline. There the deposition of sediments probably kept pace with the crustal downwarp. The subject area is between the Bahama carbonate platform and a mainly siliciclastic depositional province indicated north of Cape Hatteras. The strata are presumed to be transitional in environment of deposition. The shallow-water carbonates are likely to include many rocks with excellent reservoir properties. Source beds for petroleum, as well as shales and fine-grained carbonates and possibly evaporites, which could serve as cap rocks, should be abundant. Although compressive folding seems to be absent as a mechanism for structural growth, block faulting in the basement will serve the same purpose. High basement blocks are favorable sites for bank and reef development and commonly produce structural uplift by renewed movement. Conditions expected here present a challenge for imaginative thinking by geologists. The many similarities to such areas of prolific oil production as the Tampico-Tuxpan embayment and the Jurassic producing province in Saudi Arabia give cause for an optimistic view that giant oil accumulations may be present. Water depths over the Blake Plateau present another type of challenge to operators. The mechanical difficulties should not be insurmountable if industry has sufficient economic incentives to justify the effort. The reasonable expectation of finding oil in sufficiently large accumulations is the most basin of such incentives.

Structural History and Oil Potential of Offshore Area from Cape Hatteras to Bahamas: ABSTRACT

The present Atlantic Coastal Plain and continental shelf were parts of the crystalline Appalachians in late Paleozoic time when North America was joined to the African continent, according to current interpretation of plate tectonics. In Early Triassic time this province was uplifted by subcrustal intrusion of hot mantle material which caused a series of rift valleys to develop with trends roughly parallel with the present continental rise. This was the site of a major rift system and the convection cell which later formed the Mid-Atlantic Ridge. This rift system connected the Mediterranean Sea with the newly opened Gulf of Mexico; these were areas of extensive evaporite deposition in Late Triassic and Early Jurassic times. Normal sea water entering during Smackover (Late Jurassic) deposition permitted the growth of great carbonate banks and reefs from the Cape Hatteras area southward to the Bahamas. Active separation of Africa and North America also moved the upwelling lavas of the Mid-Atlantic Ridge away from the coastlines. Cooling of the hot mantle material under the continental margin caused downward flexing of the crust toward the ocean to form a new miogeosyncline. There the deposition of sediments probably kept pace with the crustal downwarp. The subject area is between the Bahama carbonate platform and a mainly siliciclastic depositional province indicated north of Cape Hatteras. The strata are presumed to be transitional in environment of deposition. The shallow-water carbonates are likely to include many rocks with excellent reservoir properties. Source beds for petroleum, as well as shales and fine-grained carbonates and possibly evaporites, which could serve as cap rocks, should be abundant. Although compressive folding seems to be absent as a mechanism for structural growth, block faulting in the basement will serve the same purpose. High basement blocks are favorable sites for bank and reef development and commonly produce structural uplift by renewed movement. Conditions expected here present a challenge for imaginative thinking by geologists. The many similarities to such areas of prolific oil production as the Tampico-Tuxpan embayment and the Jurassic producing province in Saudi Arabia give cause for an optimistic view that giant oil accumulations may be present. Water depths over the Blake Plateau present another type of challenge to operators. The mechanical difficulties should not be insurmountable if industry has sufficient economic incentives to justify the effort. The reasonable expectation of finding oil in sufficiently large accumulations is the most basin of such incentives.

Denkman Sandstone Member--Important Jurassic Reservoir in Mississippi, Alabama, and Florida: ABSTRACT

A clean, generally well-sorted, commonly porous, Jurassic separates marine lower Smackover carbonate mudstone from nonmarine redbeds of the Norphlet Formation in parts of southern Mississippi, southwestern Alabama, and northwestern Florida. Various workers have considered this unit to be marine, nonmarine, or a combination, and have called it basal Smackover, Norphlet, or Denkman. sandstone was proposed for this unit by Murray, who designated the Lion No. 2 Denkman, Sec. 22, T17N, R4E, Rankin County, Mississippi, as the type section. The Denkman locally exceeds 1,000 ft in thickness and is a lithologically distinct, mappable unit. Nevertheless, it is included in the Norphlet Formation by the industry and in this paper it is called the Denkman Sandstone Member of the Norphlet Formation. The Denkman is overlain generally without gradation by nonsandy basal Smackover carbonates, but is gradational downward into redbeds, the more characteristic lithology of the Norphlet. Regionally, the Denkman grades updip into conglomeratic redbeds interpreted to be alluvial fan and fluvial deposits. The Denkman sand typically consists of well-sorted, fine- to medium-grained, rounded and commonly frosted, quartz grains with some feldspar, chert, and rock fragments. The section is commonly crossbedded and does not contain fossils or carbonate beds. The Denkman usually has good permeability and intergranular porosity ranges up to 25%. Unlike beds in the Smackover, the Denkman rarely contains carbonate cement. The Denkman is reddish in its lower part and may contain s me thin shaly beds. Regional distribution of the Denkman suggests a sand source on the north and east. Stratigraphic relations, lithology, and sedimentary structures suggest a nonmarine fluvial to eolian origin for most of the Denkman sandstone. Locally the uppermost part has been reworked during Smackover transgression. The Denkman Sandstone Member marks the top of the Werner Anhydrite-Louann Salt-Norphlet Formation deposition cycle. The Denkman commonly has excellent reservoir properties and has been found productive at the Pelahatchee, Prairie Branch, Archusa Springs, East Nancy, South State Line, Big Escambia Creek, Flomaton, Little Escambia Creek, Jay, and Blackjack Creek fields. It is and will continue to be an important exploration objective along the southeast part of the Jurassic trend. End_of_Article - Last_Page 1904------------

Jurassic Sediments of Mississippi and Alabama: ABSTRACT

The writers present a regional isopachous, lithofacies, and stratigraphic study of the Jurassic sediments in the potential producing trend of Mississippi and Alabama. Jurassic deposition in the study area was affected by three major tectonic factors: a southwestward subsurface extension of the folded Appalachians, regional ancestral faulting, and salt uplift. These factors are manifested in the distribution of the sediments and in facies variations. The middle and lower Smackover is characterized by dense argillaceous carbonate deposits. Locally, a littoral facies with good sandstone porosity is present. Upper Smackover carbonate sediments are zoned into a porous sandy facies, a dense dolomitic facies, and a porous oolitic facies. Tectonic influences are first evidenced in upper Smackover sediments and appear to culminate during younger Cotton Valley deposition. Haynesville deposits (above the Smackover) include a basal Buckner Anhydrite Member and an overlying anhydritic carbonate section which grades shoreward into a porous sandy facies. Excellent reservoir rocks have been found in the transitional zone between the restricted shelf and littoral environments. The youngest Jurassic unit, the Cotton Valley, has been subdivided into the Schuler and Dorcheat facies. The Schuler facies is predominantly a coarse-grained redbed section representing a paralic environment. The Dorcheat facies is a fine-grained, open-neritic shelf deposit with grain size increasing toward the shoreline. Excellent reservoir properties are present in all Cotton Valley sandstones. End_of_Article - Last_Page 2167------------