Pinnacle Reefs Research Articles

ABSTRACT: Lithofacies Description and Reservoir Characterization of a Niagaran Pinnacle Reef, Macomb County, Michigan

ABSTRACT: Lithofacies Description and Reservoir Characterization of a Niagaran Pinnacle Reef, Macomb County, Michigan

Review of Late Jurassic Depositional Systems and Potential Hydrocarbon Plays of the Northern Gulf of Mexico Basin

ABSTRACT Post-salt Upper Jurassic siliciclastic and carbonate rocks in the East Texas/North Louisiana/Mississippi region record the early post-rift evolution of the Interior Zone rift basins of the northern Gulf of Mexico Basin. Four major river systems were fixed in space but variable in supply rate; they carried sand and mud in from the northwest (ancestral Red River), the north (ancestral Ouachita River), the northeast (ancestral Mississippi River), and the east (ancestral Alabama River). Shoal-water carbonate deposits formed when siliciclastic inputs were low and shallow-water, high-energy conditions prevailed -- usually in association with basement highs, salt swells and abandoned deltaic shelf margins. Smackover shoal-water carbonates formed within an extensive carbonate ramp from south-central Arkansas to central Texas, and were influenced by initial salt movement. Subsequent Haynesville-age Gilmer carbonate shoals in Texas rimmed rift-related high blocks, as well as highs formed by early salt movement. Siliciclastic sedimentation progressively dominated east of Shreveport, and submarine fans developed in association with a lowstand episode. During early Cotton Valley time, a major southeastward advance of the ancestral Red River delta formed the Taylor and Bossier sand series; while to the east, lower Terryville shoreline began to prograde southward in front of an expanding lagoon. During late Cotton Valley time, continued clastic sedimentation formed wave-dominated deltas in Texas and upper Terryville strike-fed sandstones in north Louisiana. At the close of Cotton Valley deposition in the earliest Cretaceous, regional transgression allowed Knowles carbonates to colonize the abandoned shelf edge and form a thick shelf-edge reef complex on its seaward slope. The significant Calvin lowstand wedge of sandstones was deposited offshore of this edge in Louisiana during a subsequent major sea-level fall, and was then covered by Winn carbonates deposited during the subsequent sea-level rise. High-potential exploration plays remain in Upper Jurassic strata. Smackover and Buckner/Gilmer shoals have produced over 10 trillion cubic feet of gas (TCFG) and 750 million barrels of oil (MMBO) in East Texas and North Louisiana, but large segments of the complex atolls along the Sabine Uplift have not been defined. Complex shoals may rim old rift-related highs such as the Sabine and Wiggins highs. The Gilmer (Cotton Valley Lime) pinnacle reefs of the Robertson-Leon trend may develop (in one form or another) over a broad swath of east-central Texas into westernmost Louisiana. Haynesville-age submarine fans may extend eastward into Mississippi. Updip Cotton Valley is an established 10-TCF tight-gas sandstone play in Texas and Louisiana, but its basinward extensions have high untapped potential. Significant high-quality Upper Cotton Valley production similar to the North Louisiana blanket sands may still be found in central Mississippi. The earliest Cretaceous (Knowles/Calvin/Winn) margin is poorly tested. Calvin-like sandstones of the lowstand wedge should occur in east-central Texas and in southwestern Mississippi.

Bulge Migration and Pinnacle Reef Development, Devonian Appalachian Foreland Basin.

Detailed stratigraphic analyses of Late Emsian and Early Eifelian (Lower to Middle Devonian) carbonate-dominated strata in the northern Appalachian Basin indicate anomalous, locally varying relative sea level changes and inversions of topography. The distribution of a major basal-bounding unconformity, basinal pinnacle reefs, local absence of parasequences, and eastward migration of shallow marine carbonate lithofacies and related biofacies in the Onondaga Limestone and underlying strata mark the retrograde migration of an elongate, northeast-southwest-trending area of positive relief, bordered on its cratonward side by a similarly migrating basin of intermediate depth. These features are thought to represent the forebulge and back-bulge basin of the Appalachian foreland basin system as it developed during a time of relative quiescence within the Acadian Orogeny. However, the relatively small size of the bulgelike feature (ca. 80-100-km-wide, 20-50-m positive relief), its great distance from the probable deformation front (>400 km), and the lack of a well-developed foredeep immediately adjacent to the bulgelike feature may indicate that it represents a smaller-scale flexural high ("flexural welt") superposed over the cratonward edge of the larger-scale classical forebulge of the basin. Development of shallow-water reefs on the crest of the bulge during sea level lowstand, followed by migration of the bulge and widespread transgression, permitted growth of economically significant pinnacle reefs in the deep basin center. Further subsurface reef exploration should concentrate along the projected position of the bulge during the basal Onondaga lowstand.

ABSTRACT: Travertine Deposits on Pinnacle Reefs in Southwestern Ontario: Implications for Paleohydrology of Middle Silurian Reefs in the Michigan Basin

This DOI is not currently attached to any metadata records. DOIs can’t actually ever be deleted (they’re persistent), but sometimes our members create DOIs in error. We do have a process to approximate deletion which we follow only in rare cases where the DOI has been genuinely created in error, and most crucially, if the DOI has never been published anywhere online or in print and never otherwise distributed to or communicated with anyone (authors, readers, reviewers, etc.

Calcified metazoans in thrombolite-stromatolite reefs of the terminal Proterozoic Nama Group, Namibia

Reefs containing abundant calcified metazoans occur at several stratigraphic levels within carbonate platforms of the terminal Proterozoic Nama Group, central and southern Namibia. The reef-bearing strata span an interval ranging from approximately 550 Ma to 543 Ma. The reefs are composed of thrombolites (clotted internal texture) and stromatolites (laminated internal texture) that form laterally continuous biostromes, isolated patch reefs, and isolated pinnacle reefs ranging in scale from a meter to several kilometers in width. Stromatolite-dominated reefs occur in depositionally updip positions within carbonate ramps, whereas thrombolite-dominated reefs occur broadly across the ramp profile and are well developed as pinnacle reefs in downdip positions.The three-dimensional morphology of reef-associated fossils was reconstructed by computer, based on digitized images of sections taken at 25-micron intervals through 15 fossil specimens and additionally supported by observations of over 90 sets of serial sections. Most variation observed in outcrop can be accounted for by a single species of cm-scale, lightly calcified goblet-shaped fossils herein described asNamacalathus hermanastesgen. et sp. nov. These fossils are characterized by a hollow stem open at both ends attached to a broadly spheroidal cup marked by a circular opening with a downturned lip and six (or seven) side holes interpreted as diagenetic features of underlying biological structure. The goblets lived atop the rough topography created by ecologically complex microbial-algal carpets; they appear to have been sessile benthos attached either to the biohermal substrate or to soft-bodied macrobenthos such as seaweeds that grew on the reef surface. The phylogenetic affinities ofNamacalathusare uncertain, although preserved morphology is consistent with a cnidarian-like bodyplan. In general aspect, these fossils resemble some of the unmineralized, radially symmetric taxa found in contemporaneous sandstones and shales, but do not appear to be closely related to the well-skeletonized bilaterian animals that radiated in younger oceans. Nama reefs demonstrate that biohermal associations of invertebrates and thrombolite-forming microorganisms antedate the Cambrian Period.

Ordovician reef-hosted Jiaodingshan Mn–Co deposit and Dawashan Mn deposit, Sichuan Province, China

The Jiaodingshan Mn–Co and Dawashan Mn deposits are located in the approximately 2-m thick Daduhe unit of the Wufengian strata of Late Ordovician (Ashgill) age. Paleogeographic reconstruction places the deposits at the time of their formation in a gulf between Chengdu submarine rise and the Kangdian continent. The Jiaodingshan and Dawashan deposits occur in algal-reef facies, the former in an atoll-like structure and the latter in a pinnacle reef. Ores are mainly composed of rhodochrosite, kutnahorite, hausmannite, braunite, manganosite, and bementite. Dark red, yellowish-pink, brown, green-gray, and black ores are massive, banded, laminated, spheroidal, and cryptalgal (oncolite, stromatolite, algal filaments) boundstones. Blue, green, and red algal fossils show in situ growth positions. Samples of high-grade Jiaodingshan and Dawashan ores assay as much as 66.7% MnO. Jiaodingshan Mn carbonate ores have mean contents of Ba, Co, and Pb somewhat higher than in Dawashan ores. Cobalt is widely distributed and strongly enriched in all rock types as compared to its crustal mean content. Cobalt is correlated with Cu, Ni, and MgO in both deposits and additionally with Ba and Zn in the Dawashan deposit. The δ 13 C PDB values of Mn carbonate ores (−7.8 to −16.3‰) indicate contributions of carbon from both seawater bicarbonate and the bacterial degradation of organic matter, the latter being 33% to 68%, assuming about −24‰ for the δ 13 C PDB of the organic matter. Host limestones derived carbon predominantly from seawater bicarbonate ( δ 13 C PDB of +0.2 to −7‰). NW-trending fault zones controlled development of lithofacies, whereas NE-trending fault zones provided pathways for movement of fluids. The source of Co, Ni, and Cu was mainly from weathering of mafic and ultramafic rocks on the Kangdian continent, whereas contemporaneous volcanic eruptions were of secondary importance. The reefs were likely mineralized during early diagenesis under shallow burial. The reefs were highly porous and acted as the locus for metasomatic replacement by Mn that combined with CO 2 produced during oxidation of organic matter in the zone of sulfate reduction and seawater bicarbonate. That metasomatic replacement formed the rhodochrosite ores.

Abstract: Paleogeographic and Sequence Stratigraphic Framework for Mesozoic Carbonate Exploration on the Northwest Gulf of Mexico (NW GOM) Rim 

ABSTRACT Mesozoic stratigraphy of the NW GOM rim from east-central Mexico to TX-LA (USA) records: (1) U. Triassic-late M. Jurassic rifting marked by creation of basement highs (e.g., Sabine uplift) and lows (e.g., Sabinas Basin, Mexico; east Texas and northern Louisiana salt basins (ETSB and NLSB)), and deposition of red beds and Callovian age salt (Louann). (2) U. Jurassic-early U. Cretaceous passive margin accumulation (15,000-20,000 ft); (3) late U. Cretaceous Laramide foreland basin development (east-central, NE Mexico) and basement reactivation. NW GOM passive margin stratigraphy consists of four 2nd-order supersequences (SS 1--U. Bathonian to L. Kimmeridgian ("158.5" - "144" myr), SS 2--L. Kimmeridgian to Berriasian ("144" - "128.5" myr), SS 3--Valanginian to L. Aptian ("128.5" - "112" myr), SS 4--L. Aptian to U. Albian ("112" - "98" myr) marked by regional patterns of facies retrogradation (2nd-order TST) overlain by facies progradation (2nd-order HST). Productive carbonate reservoirs are assigned to specific 2nd-order systems tracts of each supersequence, thus providing a predictive framework for exploitation (reservoir characterization), as well as providing a template for exploration. Rift-generated basement structures and patterns of early salt movement influenced U. Jurassic and early Cretaceous facies architecture and paleogeography, controlling the location of principally stratigraphic traps (e.g., grainstone reservoirs and pinnacle reefs of the Cotton Valley Lime/Troy Lime and James Lime in the ETSB and NLSB). Structural traps affecting Barremian Sligo and Albian Edwards reservoirs in south Texas result from a combination of post-U. Cretaceous salt-influenced tectonics and Laramide basement reactivation (e.g., Totanaca, Sabinas Basin). End_of_Record - Last_Page 361-------

Abstract: Microseepage Survey Successfully High-Grades Cotton Valley Pinnacle Reefs on Basis of Hydrocarbon Charge 

Abstract: Microseepage Survey Successfully High-Grades Cotton Valley Pinnacle Reefs on Basis of Hydrocarbon Charge 

Suppression of the acquisition footprint for seismic sequence attribute mapping

Seismic coherency has proven to be very effective in delineating geologic faults as well as considerably more subtle stratigraphic features, including channels, canyons, slumps, levees, glacial gouges, dewatering patterns and pinnacle reefs. Unfortunately, seismic coherency estimates, which quantitatively measure the similarity or dissimilarity of adjacent traces in 3-D, are particularly sensitive to coherent noise that passes through the acquisition and processing flow. They are also sensitive to dissimilarities in fold, offset, and azimuth distribution introduced through the 3-D acquisition and binning processes. Edge enhancement algorithms further exacerbate these linear artifacts. We define the acquisition footprint to be any pattern of noise that is highly correlated to the geometric distribution of sources and receivers on the earth’s surface. While the strong acquisition footprints such as those caused by normal moveout (NMO) stretch on vintage single‐fold data have been largely ameliorated by modern 2-D multifold recording, we see acquisition 3-D footprint in the low‐fold shallow section and throughout the entire section when recording sparse 3-D land surveys that often result in only six- to sevenfold data. One may partially suppress the acquisition footprint on the seismic coherency time or depth slices using conventional 2-D image processing. Unfortunately, such filtering is inappropriate for dip/azimuth maps, cluster analysis maps, and other maps that may not be continuous real variables or with maps that have cyclic values, such as the wavelet phase. We show that simple 3-D true‐amplitude dip filtering of the input 3-D (t, x, y) time- or depth‐migrated seismic data volume can be quite effective in minimizing the detrimental effect of the acquisition footprint on conventional 3-D seismic attributes for both marine and land data acquisition geometries. However, 3-D dip filtering of migrated data will often eliminate the fault‐plane reflections necessary for sharp coherency images. We therefore recommend that, whenever possible, suppression of acquisition footprint be performed before 3-D migration on the stacked data volume, where sharp fault truncations in depth are represented by smoothly varying diffractions in time.

Phanerozoic carbonate ramps from greenhouse, transitional and ice-house worlds: clues from field and modelling studies

Abstract During times of continental glaciation (e.g. Pennsylvanian-Early Permian, Miocene-Pleistocene), parasequences on carbonate platforms appear to be dominated by 400, 100 and possibly 40 ka Milankovitch climatic and eustatic changes with 50–100 m shifts in sea level. Carbonate cycles have conspicuous regional disconformities and associated aeolianites, lack tidal-flat facies except near the continental shoreline, commonly have deeper-water facies sandwiched between shallow-water deposits, and there is much unfilled accommodation. The large changes in sea level in ice-house times causes ramps to have significant gradients, thus on high-energy ramps, there can be widespread grainstone sheets. Platform tops have much depositional relief (pinnacle reefs and mounds) and erosional topography. Cycles may be highly shingled and show major lateral shifts on the ramp from cycle to cycle. During times with moderate continental ice sheets (e.g. late Mid- to Late Ordovician, Early Carboniferous), ramp cycles lack deeper-water facies, rarely have regional tidal flats but instead show widespread disconformities updip and some aeolianites. The only tidal-flat facies are developed within third-order highstand systems tracts (perhaps reflecting decreased amplitude, higher-frequency eustasy) or in downdip positions during fourth-order lowstands. Margins show moderate shingling. Grainy reservoir facies are regionally extensive, as a result of moderately large shifts of grainstone belts. Grainy facies in downslope build-ups are compartmentalized by muddy incipient drowning facies. Storm beds on the deep ramp are arranged in upward-coarsening units because of high-frequency eustasy. During global greenhouse times and little global ice (e.g. Late Cambrian-Early Ordovician, Devonian, Triassic, Cretaceous), parasequences updip on aggraded ramps are dominated by roughly 20 ka precessional cycles that formed under small (possibly <10 m or so) sea-level fluctuations, possibly coupled with an autocyclic component. The cycles typically consist of very shallow-water facies, with regional tidal flat caps and minor disconformities; cycles form layer-cake successions on the shallow ramp, and may be bundled into 100 and 400 ka sets, although ‘missing beats’ on the platform commonly obscure simple ratios typical of Milankovitch forcing. The ramps commonly have very low gradients and platforms tend to be aggraded with little topography, unless sedimentation rates are low, which results in poorly cyclic, subtidal skeletal facies over much of the ramp. Any compartmentalization of downslope subtidal build-ups is due to long-term incipient drowning events.

Carbonate production and offshore transport on a Late Jurassic carbonate ramp (Kimmeridgian, Iberian basin, NE Spain): evidence from outcrops and computer modelling

Abstract The complex interplay between shallow-water carbonate production, pelagic sedimentation, and sediment erosion and redeposition on a Kimmeridgian carbonate ramp is analysed from field data and computer modelling. Field data come from reconstructed cross-sections near Zaragoza and near Teruel, NE Spain. Inner ramp areas are dominated by coral patch reefs, ooid shoals and bioclastic packstones and grainstones, whereas middle ramp areas are typified by tempestites and pinnacle reefs. Outer ramp areas are dominated by carbonate muds and marls. The large-scale stratigraphic features of the ramp are simulated using the forward modelling computer program carbonate 6. A good match is found between real and simulated stratigraphic thicknesses along the two sections, large-scale internal stratigraphic geometries, amounts of aggradation and progradation, and the location of sequence boundaries, flooding surfaces and systems tracts in the two modelled cross-sections. To investigate the origin of the offshore carbonate mud, two synthetic stratigraphies, which both closely replicate the overall ramp geometries, were generated by computer simulation. These two simulations are based on two different hypotheses that had not been resolved from field investigation: (1) that most of the outer ramp mud was derived from erosion and redeposition from inshore areas; (2) that most of this mud originated from pelagic sedimentation. Detailed comparison between the simulated occurrence of sedimentary facies (characterized in the program by depth and process of deposition) and the real facies occurrence indicates that the closest match is given by hypothesis (1) where most of the offshore mud is produced by resedimentation from inshore areas. Offshore transport and resedimentation is thought to have been favoured by the windward orientation of the ramp, and offshore transport was highest during periods of sea-level highstands.

Abstract: Subsurface Dedolomitization in the Pinnacle Reefs of the Guelph Formation (Middle Silurian), Southwestern Ontario, Canada

Abstract: Subsurface Dedolomitization in the Pinnacle Reefs of the Guelph Formation (Middle Silurian), Southwestern Ontario, Canada

Play concepts-northwest Palawan, Philippines

The offshore area of northwest Palawan, Philippines, contains a number of provenexploration plays. These include u • pinnacle reefs developed on Nido carbonate platforms (e.g. Nido, Matinloc, Cadlao); • a seaward horst block reef fairway with large pinnacle reefs (e.g. Malampaya—Camago trend); • early Miocene Galoc Clastic Unit turbidites (e.g. Octon, Galoc); and • four-way dip closures (e.g. West Linapacan, Octon). The recent discovery by Fletcher Challenge Petroleum at Calauit Field has shown a potentialexploration play in deep-water Nido Limestone turbidites. The traditional and, to date, only economically productive play in northwest Palawan has been the Nido Limestone reefs. This paper presents a review of the old play types and presents new untested play types. These new play types include u • pre-Nido syn-rift plays; • pre-Nido marine turbidite play: and • mid-Miocene reefs. It also presents new insights into factors controlling reef development on the carbonate platforms where four reef types are now recognized. The Galoc Clastic Unit turbidite play is discussed and new play fairways presented.

Play concepts-northwest Palawan, Philippines

The offshore area of northwest Palawan, Philippines, contains a number of provenexploration plays. These include u • pinnacle reefs developed on Nido carbonate platforms (e.g. Nido, Matinloc, Cadlao); • a seaward horst block reef fairway with large pinnacle reefs (e.g. Malampaya—Camago trend); • early Miocene Galoc Clastic Unit turbidites (e.g. Octon, Galoc); and • four-way dip closures (e.g. West Linapacan, Octon). The recent discovery by Fletcher Challenge Petroleum at Calauit Field has shown a potentialexploration play in deep-water Nido Limestone turbidites. The traditional and, to date, only economically productive play in northwest Palawan has been the Nido Limestone reefs. This paper presents a review of the old play types and presents new untested play types. These new play types include u • pre-Nido syn-rift plays; • pre-Nido marine turbidite play: and • mid-Miocene reefs. It also presents new insights into factors controlling reef development on the carbonate platforms where four reef types are now recognized. The Galoc Clastic Unit turbidite play is discussed and new play fairways presented.

The pinnacle reefs of Jabaloyas (Late Kimmeridgian, NE Spain): Vertical zonationand associated facies related to sea level changes.

The pinnacle reefs of Jabaloyas (Late Kimmeridgian, NE Spain): Vertical zonationand associated facies related to sea level changes.

Mesoproterozoic deep‐water reefs from Borden Peninsula, Arctic Canada

ABSTRACTA superbly exposed stromatolite reef complex occurs in the Victor Bay Formation near Strathcona River on northern Baffin Island. Individual reefs are up to 130 m thick and nearly 1 km in length, and their development was clearly related to their position in the facies spectrum and to sea‐level dynamics. In the first sea‐level cycle, metre‐scale reefs grew amongst mid‐ramp calcarenites and outer‐ramp shales during slow sea‐level rise; a 25‐m‐thick oblate reef tract, separating mid‐ramp and outer‐ramp facies, formed during the highstand. The greatest period of reef growth was during the second sea‐level cycle. Pinnacle reefs nucleated on the karsted upper surface of the oblate reef tract and aggraded rapidly in response to rising sea‐level, producing structures with more than 75 m of depositional relief. A gradual symmetrical succession of stromatolite growth forms, from stratiform to cylindrical columns to conical columns and then back through cylindrical columns to stratiform, is mirrored by evidence in offreef deposits for deepening to a maximum flooding surface and then shallowing. The tops of these high‐standing reefs were karsted during the following regression, while dolomite ‘cryptodomes’ grew as sheets on their submerged flanks and as progradational tongues extending basinward of the reefs. Continued sea‐level fall resulted in subaerial exposure of the entire reef complex and the extensive formation of surface and subsurface karst.These Proterozoic slope buildups are similar to Phanerozoic deep‐water reefs in size, shape, prevalence of synsedimentary lithification, presence of Neptunian dykes and in their well‐developed vertical zonation of reefbuilders. However, they differ in being constructed exclusively by stromatolites rather than being mud mounds with small skeletal elements, and in lacking halos of perireefal sand‐ and gravel‐sized calcareous debris. Their responses to changes in sea‐level were strikingly similar to those shown by their younger counterparts, and suggest that sequence‐stratigraphic concepts derived from studies of Phanerozoic reefs can also be applied to the Proterozoic.

96/05710 Paying for the future — Securing investment in Britain's oil and gas industry

This paper discusses the use of a 2-D numerical model representing a typical depleted pinnacle reef reservoir to generate synthetic data for multiple CO2 injection periods after a prolonged period of oil and gas production. The data are analyzed with conventional pressure-transient analysis and injectivity-index approaches from petroleum reservoir engineering practice.Pressure falloff data from multiple shut-in periods, with and without boundary effects, indicate that the system response is similar to that of a composite reservoir with different total mobility and total compressibility values in the inner (CO2-rich) and outer (CO2-free) regions. The total mobility of the inner zone can be approximated by the total mobility of the gas phase in the vicinity of the CO2-oil front, while the total mobility of the outer zone corresponds to the total mobility of the oil phase in the undisturbed region.The injectivity index, calculated as injection rate divided by the pressure buildup from reference conditions, yields a quasi-stable value during the transient period which can be correlated to the permeability-thickness product of the injection zone. During the boundary-dominated (pseudo-steady-state) period, a flowing material balance plot can be utilized to determine an apparent injectivity index, which is higher than the true injectivity index because of multi-phase skin effects.

Trap and Seal Analysis in Carbonate Shelf Margin Stratigraphic Trap Exploration; Example from the Lower Miocene, Zhujiang Formation, Pearl River Mouth Basin, People's Republic of China: ABSTRACT

Carbonate shelf margin stratigraphic traps are a particularly risky play type because the same diagenetic factors responsible for secondary reservoir quality enhancement can be responsible for degrading seal quality and increasing trap risk. The Zhujiang Fm. prograded westward off the Dongsha Massif initially as a ramp which evolved into a prograding and aggrading shelf margin. Seismic interval velocity analysis, modeled with data from a nearby oil-bearing pinnacle reef, indicates a thick porosity zone at the shelf margin, wedging and pinching out eastward. Core data from the pinnacle reef indicated a short-term exposure event was responsible for significant early secondary porosity enhancement. This also may have influenced the adjacent shelf area; enhancing porosity in the shelf margin, but reducing seal capacity in the equivalent up-dip shelf sequence. The seal competency of the overlying Hanjiang shales was demonstrated by hydrocarbons sealed in the adjacent pinnacle reef. Seal risk was evaluated by mercury injection capillary pressure analysis in a shelf carbonate well updip from the margin. It was determined that the up-dip shelf seal is sufficient to hold an economically favorable 300-500 ft (90-150 m) hydrocarbon column. Seismic evidence revealed several large mega-slumped portions of the shelf margin producing scalloped areas extending severalmore » kilometers back into the shelf. Subsequent filling of these reentrants could produce lateral sealing by juxtaposing Hanjiang shales against the sides of the remnant Zhujiang carbonate salient. The slump scar on the south side of the salient did not downcut to a significant stratigraphic depth to provide a critical closure to trap a minimum hydrocarbon column to meet economic thresholds.« less

Cotton Valley Lime Pinnacle Reef Play: Branton Field

A frontier play for gas-charged Jurassic carbonate buildups, interpreted as pinnacle reefs, is under way along the western shelf of the East Texas Basin. Scattered reef-type features 200-800 ac in size have been identified thus far over an area approximately 6 mi (10 km) wide by 50 mi (80 km) long. As of January 1996, four new fields had been discovered with individual well productivities of 9-30 Mcf (FOOTNOTE *) gas/day and per-well reserves of 5-75 Gcf (FOOTNOTE *) gas. This paper presents new well log, 3-D seismic, and other information indicating the basic structural and depositional character of these features through a focus on Branton field (Leon County). These data strongly suggest the regional potential of the play and highlight the value gained by reevaluating k own provinces in the light of new interpretive schemes and technology.

The 1991–1992 rapid ecological assessment of Palau’s coral reefs

At the request of the Palau and US governments, a team of 30 scientists under the leadership of the Nature Conservancy completed a rapid ecological assessment (REA) of nearshore marine resources in Palau in 1992. The REA provided ecological input to Palau’s ongoing master plan for economic development and identified 45 marine sites worthy of special protection. The REA relied on previous literature, 1992 aerial photography, interviews, and field observations. A combination of qualitative and quantitative techniques were used to assess stony corals, other reef invertebrates, reef and shore fishes, macroscopic algae, seagrasses, sea turtles and other marine organisms. The REA covered a variety of coral reef habitats including beaches, seagrass beds, fringing reefs, lagoons, passes, channels, reef holes, patch and pinnacle reefs, barrier reefs, atolls, submerged reefs, mangroves, and “rock” islands. Major stresses to Palau’s coral reefs include sedimentation from soil erosion, overfishing, and damage from periodic storms and waves. Minor stresses include dredge-and fill activities, sewage pollution, anchor damage, tourism use, ship groundings, aquarium fish collecting, and minor crown-of-thorns (Acanthaster) infestations.