South-central Louisiana Research Articles

Behavior and Movements of Largemouth Bass in Response to Salinity

Abstract Salinity preferences of adult and young-of-the-year largemouth bass Micropterus salmoides from a freshwater lake and a brackish marsh in south-central Louisiana were tested at 22°C in salinity-gradient chambers (0, 3, 6, 9, and 12‰ salinity) under a photoperiod of 12 h light 12 h dark. Young largemouth bass from both collection sites preferred 0‰ salinity. Although adult marsh and freshwater largemouth bass preferred 3‰ salinity, differences in salinity selection were noted: mean number of observations at 0‰ salinity was significantly greater for freshwater fish, whereas mean number of observations at 3‰ salinity was significantly greater for marsh fish. Salinity preferences were not affected by prior acclimation of fish to salinities of 0 or 5‰. Salinities of less than 5‰ did not influence short-term (daily) movements of marsh fish implanted with ultrasonic transmitters. Although no tagged largemouth bass could be located in the marsh after salinities exceeded 5‰, marsh largemouth bass smaller t...

Internal Kinematics of Salt Diapirs: DISCUSSION

Iklbot and Jackson (1987) presented a very good sum­ mary of several aspects of salt-stock configuration and emplacement as applied to the United States Gulf Coast. One aspect of this emplacement is a process they describe as nested toroidal stream surfaces (Iklbot and Jack­ son, 1987, p. 1083. their Figure 11) or toroidal flow. The concept may have been originally suggested by the over­ turned and even convoluted salt structures observed at the Boulby mine in England (a highly deformed beddedsalt deposit). Concepts about these structures have been expanded upon by experiments, hydrodynamic theory, and further observations. Toroidal-type swirl struc­ tures develop early and are best displayed in salt in the early stages of deformation and diapir rise. My main purpose here is to note that Tiilbot and Jack­ son (1987) have apphed these toroidal shapes where they do not seem to apply—the high-rise diapirs of the Five Island salt stocks of south-central Louisiana. As a result, Iklbot and Jackson have suggested an unlikely origin for the spines in these stocks. They further infer that these toroidal structures should be present in mature-type salt diapirs of the Gulf Coast coastal prov­ ince; these diapirs have been well explored for petroleum. Tklbot and Jackson (1987, p. 1068) stated that mature diapirs can form crestal bulbs.... I suggest that these are unlikely assumptions. I have emphasized (for example, Kupfer, 1970a, p. 43, p. 55-56; 1988, p. 14) the distinctly different structural styles within low-rise salt diapirs exemplified by north German diapirs (with toroidal structures, for example Iklbot and Jackson's [1987] Figures 5 and 15) and the high-rise diapirs of coastal Louisiana. The Five Islands (from north to south: Jefferson, Avery, Weeks, Cote Blanche, Belle Isle) are over the deepest part of the Gulf Coast basin (60,000 ft or 18 km) and represent an extreme case of high rise above the present mother-salt hori­ zon. As Iklbot and Jackson have noted (1987, p. 1074, 1084), the salt at the top of these stocks has moved about 19 mi (30 km), is highly refolded, and the flow inside the diapirs is neither homogeneous nor simple. These stocks are complex and have lost or distorted nearly all of their early formed structures. Much of Tklbot and Jackson's experience (and evi­ dence cited in their paper) has been with salt glaciers, early diapirism, and with the intermediate-rise diapirs of eastern Texas (and northern Louisiana) .These interme­ diate stocks, as might be expected, retain much of the

An Application of the Stock Adjustment Model in Estimating Employment Multipliers for the South Central Louisiana Petroleum Economy 1964–84

ABSTRACTThe South Central Louisiana Petroleum Economy received an economic rent from its petroleum resources during the energy crisis of the 1970s and early 80s. A differential export‐base model incorporating a geometric lag was developed for estimating dynamic employment multipliers. This technique is especially applicable to regional economies in which exports are a major economic factor. Employment multipliers were estimated using ordinary least squares (OLS) regression. Results from the analysis indicate that agriculture, oil and gas mining, and manufacturing are highly significant employment generators. Both long‐run and short‐run employment multipliers were derived from the model. It is estimated that a five‐dollar change in the real price of crude oil will result in a long‐run employment change of 8,027 for the oil and gas mining industry. Based on estimates of the long‐run multiplier, this will result in a total employment change of 28,014 for this economy.

Recognition of Depositional Environments Using Programmed Pyrolysis: Sparta Formation, South-Central Louisiana: ABSTRACT

Programmed pyrolysis of mudstone provides a rapid and effective technique to recognize environments of deposition in the subsurface. Ninety-three mudstone samples from four downdip Sparta Formation wells in south-central Louisiana were analyzed using a Rock-Eval pyrolysis analyzer with total organic carbon (TOC) module. TOC and the hydrogen index were found to be the most useful parameters for distinguishing depositional environments. Detailed conventional core analysis demonstrates that the Sparta Formation in the study area represents a prograding barrier island complex consisting of reservoir quality shoreface, storm-washover, and tidal-inlet sandstone. The sandstone overlies open marine mudstone and is capped by lagoonal mudstone. Mudstone of both facies is characteristically dark brown to black, laminated, and organic rich. However, pyrolysis results reveal geochemical contrasts that can be used to distinguish between the marine mudstone facies and the lagoonal mudstone facies. Lagoonal mudstone has TOC values averaging 1.37% and hydrogen indices averaging 160. In contrast, offshore marine mudstone has much higher TOC values, which average 2.61%, and a dramatically higher average hydrogen index of 341. Average T/sub max/ of mudstone from both facies is 431/degrees/C, and S/sub 1//S/sub 2/ ratios are well below unity, showing that the Sparta Formation is thermally immature in the studymore » area. Thermal maturity differences cannot be invoked to explain the observed geochemical differences between environments. The clear contrast of organic geochemical differences between environments. The clear contrast of organic geochemical parameters is interpreted to reflect dissimilarity in kerogen types and in modes of preservation between mudstone facies. Lagoonal mudstone contains mostly terrestrial kerogen, whereas more oil-prone marine kerogen predominates in marine mudstone.« less

Origin of Crude Oil in the Wilcox Trend of Louisiana and Mississippi: Evidence of Long-Range Migration: ABSTRACT

ABSTRACT Geochemical characterization of crude oils from Wilcox reservoirs in central Louisiana and southwest Mississippi suggests that they represent a single crude oil family that is distinct when compared to crude oils in deeper Tuscaloosa and Smackover reservoirs. This observation is consistent with geologic constraints that suggest an origin of crude oil from within the Wilcox Group itself. Although shales of the shallow Wilcox Group in central Louisiana and southwest Mississippi contain gas-prone kerogen and are thermally immature, a more oil-prone source facies is present in marine shales of the deep Wilcox Group in southcentral Louisiana. Thermal maturity measurements based on pyrolysis suggest a broad area of effective Wilcox source rock in southcentral Louisiana. Migration distances from source to reservoir rocks of the downdip Wilcox Trend of southcentral Louisiana appear to be relatively short. However, long-range updip migration (sometimes greater than 100 km) from deeply buried Wilcox source facies provides the best explanation for emplacement of crude oil in the shallow Wilcox Trend of central Louisiana and southwest Mississippi.

Facies Control on Reservoir Properties within a Barrier Island Complex, Sparta Formation, Pointe Coupee Parish, Louisiana: ABSTRACT

Analysis of conventional core, well logs, and petrophysical data has yielded an interpretation of the Sparta B sandstone in south-central Louisiana as a prograding barrier island complex. Four sedimentary facies possess reservoir potential: lower shoreface, upper shoreface, storm washover, and tidal-inlet channel sandstone facies. Distinct porosity and permeability values are associated with each reservoir facies. Predictable porosity and permeability trends associated with the Sparta B sandstone barrier island complex allows for identification of distinct fluid flow units within the sequence. In addition, individual sedimentary facies possess characteristic well log signatures; therefore, the geometry, thickness variability, and lateral continuity of each fluid flow unit can be determined and heterogeneities within the reservoir interval can be resolved.

Distribution, Abundance, and Sampling of Fall Armyworm (Lepidoptera: Noctuidae) in South-central Louisiana Cornfields

Fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), were sampled from cornfields at the St. Gabriel Experiment Station in south-central Louisiana from 1981 to 1983. Data from single-plant samples and five-plant samples for small, medium, and large larvae and total population were fitted to the Poisson, negative binomial, and Neyman type-A distributions, as well as the Taylor power function. None of the three distributions fit FAW populations consistently. The power function provided significant regressions for all eight larval categories and was used to calculate number of samples required for different larval densities for a given confidence level.

Effects of Primary Sedimentary Processes on Reservoir Quality of Deep Wilcox"(Eocene) Sandstones in Fordoche Field, Louisiana: ABSTRACT"

The initial discovery and subsequent development of Fordoche field established a Deep Wilcox production trend in south-central Louisiana. Production in the field occurs within five intervals: the W4, W5, W8, W12, and W15 sandstones. The W8 and W12 sandstones are the most prolific. They represent shoreface sequences which formed at or near the shelf margin. Cumulative hydrocarbon production from these sandstones is in excess of 22 million bbl of oil and 151 bcf of gas. Over 1100 ft (335 m) of conventional core from the W8 and W12 sandstones in six wells were analyzed and compared to petrophysical data to effectively characterize reservoir quality. Primary sedimentation patterns (i.e., physical and biogenic sedimentary structures and sequences) are the dominant control on reservoir quality throughout the field. Burrowed to bioturbated (> 75% burrowed) lower shoreface sandstones possess relatively high average porosity values (16.7%); however, permeability values are extremely low (< 0.2 md). Clay-lined burrow walls create numerous permeability barriers which significantly alter fluid flow patterns within this facies. In contrast, massive to burrowed middle shoreface sandstones, although possessing similar average porosity values (19.8%), have substantially higher average permeability values (8.6 md). Within the middle shoreface facies, higher wave energies winnow the fine-grainedmore » silts and clays, resulting in the deposition of a clean, well-sorted sandstone. The entire sequence coarsens upward in both grain size and percent sand and is overlain by a thin (3.5 ft; 1.0 m), tightly cemented calcareous sandstone. Average thickness of the middle shoreface facies in Fordoche field is 23 ft (7.0 m) with stacked sequences within the W12 sandstone as thick as 57 ft (17.4 m) of high reservoir quality sandstones.« less

Occurrence of Pseudophragmina sp. as a Possible Indication of Carbonate Bank Deposition in Upper Wilcox (Paleocene-Eocene), Pointe Coupee Parish, Louisiana: ABSTRACT

Paleontologic and sedimentologic analysis of whole-diameter cores from two upper Wilcox sandstones in south-central Louisiana suggests the presence of carbonate bank deposition during the late Wilcox. The larger foraminifera Pseudophragmina sp. occurs in two stratigraphically unrelated sandstones from the upper Wilcox (Paleocene-Eocene) in Pointe Coupee Parish, Louisiana. In Bayou Fordoche field, Pseudophragmina sp. is dispersed throughout an uppermost Wilcox sandstone, which is a 6-m thick unit found 82-m below the top of the Wilcox. In Fordoche field, which is south and down dip of Bayou Fordoche field, numerous individuals of Pseudophragmina sp. are concentrated in two distinct zones within the W-12 sandstone, a relatively thicker (33 m) sandstone that occurs 320 m below the top of the Wilcox. The down dip W-12 sandstone is stratigraphically unrelated to the updip sandstone; however, the two sandstones are lithologically and faunally similar. The updip sandstone and the Pseudophragmina sp. bearing intervals in the down dip W-12 sandstone are quartzose and glauconitic. In addition to numerous Pseudophragmina sp., they contain globorotalid and globigerinid planktonic foraminifera and smaller benthic foraminifera from such groups as miliolids, lagenids, and nodosarids. Echinoids and mollusks are also present. These fossils are dispersed throughout the updip sandstone and are concentratedmore » in two separate zones within the down dip W-12 sandstone. This Pseudophragmina facies in the upper Wilcox is faunally and lithologically similar to facies that are related to modern submarine carbonate banks in the Gulf of Mexico and to reef facies reported for subsurface Tertiary units in the Gulf Coast.« less

Seasonality of Materials Transport through a Coastal Freshwater Marsh: Riverine versus Tidal Forcing

Transports of nitrate and suspended solids were measured six times from January 1984 until January 1985 in a small freshwater tidal bayou in south-central Louisiana. The bayou and adjacent marshes are influenced by Atchafalaya River discharges, tides, and coastal weather patterns. Large net ebb-directed water transports occurred in winter, spring, and summer, coincident with high river discharges, indicating riverine dominance. A very small net flood-directed water transport occurred in fall, indicating tidally dominated hydrology. Nitrate and suspended solids transports were net ebb-directed in all seasons, but were two orders of magnitude higher during high river flow. Exports changed as hydrology switched from river dominated to tidally dominated, and as concentrations of materials changed. Comparison of suspended solids and nitrate concentrations in the river and bayou shows that these materials were usually lower in the bayou, indicating retention by the marsh/aquatic system.

Shelf-Margin Sedimentation in Wilcox Group, South-Central Louisiana: ABSTRACT

Shelf-Margin Sedimentation in Wilcox Group, South-Central Louisiana: ABSTRACT

Sedimentary Environments, Evolution, and Stratigraphic Framework of Laterally Prograding Transgressive Barrier Complex: Timbalier Island, Louisiana: ABSTRACT

Timbalier Island is a beach-ridge barrier flanking the abandoned late Lafourche deltaic lobe on the south-central Louisiana coast. Twenty-five vibracores (5-9 m) and 12 short cores were acquired in a variety of sub-aerial, intertidal, and subaqueous environments of this barrier complex. These cores, coupled with detailed shoreline change maps, indicate that the island's migration, evolution, and stratigraphy are complex and variable. Since 1887, Timbalier Island has laterally migrated approximately 6 km to the northwest, while the adjacent inlet (Cat Island Pass) migrated 2.5 km. Due to this extensive lateral progradation at the western end of the island, the following sequence is found: (1) bay/lagoon, (2) lowerspit platform/shoreface, (3) upper spit platform/shoreface, (4) foreshore, (5) backbeach, and (6) dune. An upward decrease in burrowing and increase in physical sedimentary structures, grain size, percent sand, and sorting are observed. None of the cored sequences resemble the tidal inlet channel-spit platform models observed elsewhere but, instead, mimic regressive shoreface sequences. During the island's evolution, the interior beach ridges subsided in response to compactional subsidence and became vegetated by a Spartina and Avicennia (mangrove) marsh. In this central-interior part of the island, the progradational sequence is capped by an aggradational (0.5-1 m thick) marshmore » deposit.« less

Foraminiferal Biostratigraphy and Paleoecology of Wilcox Group (Paleocene-Eocene), Central Louisiana: ABSTRACT

The Wilcox Group in east-central and south-central Louisiana consists of 300-1200 m of mostly clastic marine and nonmarine deposits. Detailed micropaleontologic studies of the Wilcox Group in Louisiana are not available because the strata are generally unfossiliferous, especially in the northern, updip part of the study area. However, the present foraminiferal study, done in conjunction with a comprehensive regional investigation, has yielded significant biostratigraphic and paleoenvironmental information. Well cuttings and conventional cores from wells drilled by various oil companies into Wilcox units in Allen, Avoyelles, St. Landry, St. Martin, and Pointe Coupee parishes contain planktonic foraminifera that permit their assignment to established regional and worldwide zonation schemes. The section ranges from the Paleocene to the Eocene, and includes the Globorotalia angulata, G. pusilla, G. pseudomenardii, G. velascoensis, and G. subbotinae zones. Samples from conventional cores drilled through the Wilcox section throughout the study area yield benthic foraminiferal faunas that are dominated by agglutinated species and represent marine environments that range from the inner continental shelf to the continental slope. Core samples of glauconitic sandstones from the uppermost part of the section contain faunas that are dominated by Discocyclina sp. and other species of calcareous larger foraminifera. These faunas indicate shallow-watermore » continental-shelf paleoenvironments. Many of the producing reservoir sandstones in the downdip part of the study area are stratigraphic traps of a marine depositional origin. This foraminiferal study, in conjunction with the ongoing regional Wilcox synthesis, will yield insight to similar producing trends in the downdip parts of the upper Wilcox.« less

Evidence for Large-Scale Vertical Migration of Dissolved Fatty Acids in Louisiana Oil Field Brines: Iberia Field, South-Central Louisiana: ABSTRACT

ABSTRACT There is considerable interest at the present time in the origin and distribution of dissolved volatile fatty acids (VFAs) in oil-field brines. This interest has developed as a result of the recognition of the role these compounds may play: 1) in subsurface acid attack and porosity enhancement, 2) as precursors of natural gas, and 3) as possible proximity indicators of hydrocarbon accumulations. The detailed study of the distribution of dissolved VFAs on a field scale provides much useful information on processes of generation, transport, and degradation of these compounds. At the Iberia oil field, one of several fields we have studied in the Tertiary section of South-Central Louisiana, spatial variations in pore water compositions and temperatures indicate the presence of an on-going, dynamic, subsurface circulation system. Deep brines with VFA levels in excess of 150 mg/1 are migrating up the south flank of the Iberia salt dome a vertical distance of at least 2 km (6000 ft). The VFAs in these waters are dominated by acetate and propionate. As these waters ascend, they mix with an ambient mass of water having total VFA concentrations of 20 mg/1 or less and dominated by n-butyrate. Preferential decarboxylations of acetate and propionate relative to iso- and n-butyrate and iso- and n-valerate are occurring in this system. The byproducts of these decarboxylation reactions should be methane, ethane, and bicarbonate. Temperatures are cool enough (<80°C) in the shallower parts of the sequence to permit the existence of bacteria that coud break down acetate through fermentation. The spatial distribution of individual dissolved VFA's is complex but systematic, and must ultimately be related to the rates of advective transport, dispersive mixing, and chemical reaction. We believe that a potential new application of the study of these dissolved organic compounds lies in helping to unravel the dynamics of some types of subsurface flow systems.

The dynamics of a river‐bay‐delta system

An analysis has been made to aid our understanding of various phenomena associated with turbulent plane jets that issue from river outlets and discharge into quiescent bays. An integrated form of the hydrodynamic equations of flow continuity and momentum balance, coupled with advective‐diffusion mass transport equations, has been formulated into a two‐dimensional spatial domain. Closed‐form analytical solutions are obtained with the aid of similarity functions for the velocity and sediment concentration profiles. A numerical procedure for estimating the areal and volume deposition of the delta sediments is presented. The Atchafalaya River Delta, a newly developing delta in the south central Louisiana Coast, is used to illustrate analytical techniques. The results of analytical predictions are compared with the results predicted by other statistical and generic approaches; an agreement is found. A sensitivity analysis is performed to assess the relative importance of various parameters in the river‐bay‐delta system.

Shear and Compressional-Wave Surface and Downhole Tests in Southern Louisiana: ABSTRACT

Shear- and compressional-wave seismic tests using the Vibroseis system were performed near a well in south-central Louisiana to study acquisition, processing, and interpretation problems typically encountered in low-velocity, relatively uncompacted Gulf Coast sediments. The primary objectives envisioned for these tests were to improve S-wave data quality by studying surface noise patterns to optimize source and receiver arrays, provide a direct correlation of P- and S-wave seismic data by using vertical seismic profiles (VSP), and measure the decay of P- and S-wave seismic energy with depth by using a downhole geophone. To achieve these objectives, an expanding reflection profile (ERP), a walkaway noise analysis, and a VSP were recorded with both S- and P-wave sources. The S-wave ERP shows reasonable data quality although it was very band-limited (5-12 Hz). In contrast, the P-wave data quality is excellent. The difference in data quality is primarily due to strong, source-generated End_Page 465------------------------------ noise from the S-wave vibrators. Time-depth data available from the S- and P-wave VSPs were used to convert the time sections to depth, and hence provide the best visual tie of common reflecting horizons. The accuracy of the ties is mainly limited by the poor signal-to-noise ratio and narrow bandwidth of the S-wave data. Finally, energy decay measurements from first breaks on VSP data show that S waves have a higher loss than P waves in the near surface. However, below 3,000 ft (915 m), the slopes of the energy decay curves are similar, thus implying S-wave data quality will not deteriorate faster than P-wave data quality at greater depths. End_of_Article - Last_Page 466------------

Local Sea Level Change and Future of Louisiana Coast: ABSTRACT

The relative elevation of sea and land has been changing through time in response to two fundamentally different groups of factors. Global factors include changes in the volume of the ocean basins owing to tectonic processes and changes in the total amount of ocean water due to glaciation. Local factors include subsidence of continental margins and compaction of recent sediments. Over this century, global sea level (eustatic) appears to have been rising at a rate of 1.2 mm per year. Along the south-central Louisiana coast the land surface appears to be sinking at a rate of about 8 mm per year. Recent global climatic modeling suggests strongly that we are about to enter a period of rapidly accelerating warming due to increased amounts of carbon dioxide in the atmosphere. As a consequence, eustatic sea level rise is predicted to accelerate because of both steric expansion of the ocean water and continued melting of polar ice caps. For the next 40 years the eustatic sea level rise may average 10 mm per year. The local relative sea level in coastal Louisiana would therefore rise at about twice its present rate over this time period. At this rate, local sea level will, in the year 2020, stand some 70 to 75 cm (2.3 to 2.5 ft) higher than at present. The numbers presented above are average values for the Louisiana coastal plain. Local variability in subsidence rate appears to be related to the thickness of Holocene sediments. The highest rates of subsidence are found in the modern Mississippi (birdfoot) delta and in coastal Terrebonne Parish above the late Pleistocene Mississippi trench; in both areas the Holocene section is in excess of 200 m (650 ft) thick. The high rate of local sea level rise along the Louisiana coast makes it imperative that plans for coastal development and protection consider the long-term consequences of sea level change. End_of_Article - Last_Page 1469------------

Reactivation of Fault Movement, Tepetate Fault Zone, South-Central Louisiana: ABSTRACT

The Tepetate fault zone consists of a series of faults trending east-west along the northern margin of the South Louisiana salt dome basin. The fault is known to be currently active in the Baton Rouge area, where it has fractured and displaced pavement and foundations. Detailed subsurface mapping of the fault zone in an area of Pointe Coupee Parish to the west reveals that there have been two distinct periods of growth faulting, separated by a long period of inactivity. The first period of fault activity occurred during the time from Wilcox (or earlier) to Frio deposition. There then followed a period of quiescence characterized by deposition of nearly 8,000 ft (2,400 m) of fluvial sands and shales, primarily of Miocene age. In more recent times, probably Pleistocene, the fault has been reactivated, and up to 40 ft (12 m) of additional displacement has occurred in the area studied. Of concern is the fact that a site near this fault has been proposed for the surface and subsurface disposal of hazardous wastes. Recognition of the interruption and reactivation of growth faulting in south Louisiana is of considerable importance with regard to problems of regional structural evolution, fluid migration, and the siting of surface and subsurface waste-disposal facilities. Because of difficulties in subsurface correlation, faults of small displacement in fluvial sequences can easily be overlooked. Further detailed study, however, is warranted. End_of_Article - Last_Page 1431------------

Louisiana Tuscaloosa Versus Southeast Texas Woodbine: ABSTRACT

The deep Tuscaloosa play extending across south-central Louisiana has resulted in the recent discovery of large gas reserves. This same downdip lower Upper Cretaceous interval, known as the Woodbine in southeast Texas, extends into Texas across Newton, Jasper, Polk, and Tyler Counties. Although well control is sparse through this interval in southeast Texas, available data suggest a different depositional and structural setting for the lower Upper Cretaceous interval. No thick units of sands are within the interval, and most of the production has been found in stratigraphic traps exhibiting thin sands, as in the Seven Oaks field. Subsurface studies of the lower Upper Cretaceous interval across south-central Louisiana and into southeast Texas indicate it is unlikely the Louisiana Tuscaloosa play will extend into the southeast Texas area. However, there is sparse downdip control in Texas south of the Lower Cretaceous shelf edge and it is, therefore, possible that some sands have been deposited subparallel to the shelf. The best area to explore for this possibility would be south of the 1,000-ft Tuscaloosa or Woodbine isopachous contour which extends across southeast Texas. End_of_Article - Last_Page 1558------------

False River Field: ABSTRACT

On August 14, 1975, Chevron Oil Co. spudded the No. 1 Alma Plantation in Sec. 87, T6S, R11E, Pointe Coupee Parish, Louisiana. The objective was in Cretaceous rocks at a projected total depth of 22,500 ft (6,858 m). This became the discovery well for False River field. To this date, nine wells have been completed in the field from the Tuscaloosa Formation of early Late Cretaceous age at a depth of 19,800 ft (6,035 m). In addition, seven wells are being drilled or tested, and two have been completed as dry holes. The No. 1 Alma Plantation flowed at the rate of 20 MMcf of gas per day with a flowing tubing pressure of 11,600 psig (79,878 kPa). The initial shut-in reservoir pressure was 16,806 psig (115,776 kPa). From subsurface and seismic data, a structure appears to be buri d below the base of the Austin Chalk. This structure is 20-mi (32 km) long and 10-mi (16 km) wide at a depth of approximately 19,000 ft (5,791 m), and is situated adjacent to the south side of a Cretaceous hinge line. This hinge line extends from Lake Bornge northwesterly across south-central Louisiana into southern Vernon Parish. From subsurface and seismic data it appears that the structure is depositional in origin. End_of_Article - Last_Page 720------------