Louisiana Continental Shelf Research Articles

Developments in Louisiana Gulf Coast in 1974

The Louisiana Gulf Coast region consists of the 38 southern parishes of Louisiana and 21 continental shelf areas extending out to the 6,500-ft water-depth limit. There were 1,724 exploratory and development wells drilled in 1974, a decrease of 12% from the previous year. Of the exploratory wells, 21% were successful. Success for development wells was 67% for 1974. A total of 23 significant new-field discoveries was drilled in 1974, 10 onshore and 12 offshore. The most important are South Timbalier Block 37, Eugene Island Block 367, Jennings Townsite, Raccoon Lake, North Vinton, West Johnson's Bayou, and Hopedale Lagoon. The most significant of the new pools and extensions are Eugene Island Block 313, South Pass Block 62, South Marsh Island Block 128, Vermilion Block 331, Pecan Island, Pine Prairie, Mystic Bayou, and Golden Meadow. Geophysical activity increased 4% onshore and 8% offshore. Evaluation of recently acquired leases and anticipation of future sales account for the increase offshore. Record amounts were bid for leases offshore in March 1974, and royalty bidding was introduced at the October Federal Lease Sale.

Late Pliocene-Early Pleistocene Nannofossil Stratigraphy in North-Central Gulf Coast: ABSTRACT

The early Pleistocene deposits of southeastern Louisiana consist of basal regressive sandstone overlain by a thick marine transgressive shale unit to which various informal names have been applied. This early Pleistocene shale has an areal extent of more than 20,000 sq mi and ranges in thickness from 100 ft in updip areas to several thousand feet in the continental shelf. This study was based on sidewall cores from 4 wells drilled more than 60 mi offshore from the coastline in the southern part of the Ship Shoal area, Terrebonne Parish, Louisiana. Samples also were examined from piston cores taken in the Atlantic and Pacific Oceans and the distribution of pertinent calcareous nannofossils in these samples was compared with distributions in the Louisiana sections. End_Page 1836------------------------------ Thirty-two species of calcareous nannofossils from 20 genera have been identified from the late Pliocene and early Pleistocene strata of the Louisiana continental shelf. Of these 32 species, 2 are restricted sufficiently to be useful as stratigraphic criteria. The significant occurrences are, the extinction of Discoaster brouweri Tan Sin Hok and the first appearance of Gephyrocapsa caribbeanica Boudreaux and Hay and these 2 species may be used to define the base of the early Pleistocene marine shale in the north-central Gulf Coast. Other results include: (1) delineation of a phylogenetic series extending from Coccolithus doronicoides Black and Barnes in the middle Pliocene section to Emiliania huxleyi (Lohmann) in the Holocene, (2) recognition of the co-occurrence of Ceratolithus cris atus (Kamptner) and Ceratolithus rugosus Bukry and Bramlette in the earliest Pleistocene sediments, (3) extension of the geologic range of Gephyrocapsa protohuxleyi McIntyre and Cricolithus jonesi Cohen back to the early Pleistocene, and (4) the first reported fossil record of Homozygosphaera wettsteini (Kamptner) and Calyptrosphaera oblonga Lohmann. End_of_Article - Last_Page 1837------------

Correlation of early quaternary events in the U.S. Gulf Coast

A reexamination of the sequences of planktonic foraminifers and calcareous nannoplankton in the Plio-Pleistocene sediments beneath the Louisiana continental shelf has been undertaken in order to modernize correlation schemes that were established 10–20 y.a. As a consequence, it can be shown that (1) a new correlation of marine micropaleontological and continental glacial events is necessary; (2) the Gulf Coast faunal events can be reliably correlated with those in the type Italian Pleistocene section and in the deep-sea cores; (3) it is becoming increasingly evident that it is invalid to correlate the Plio-Pleistocene boundary, as defined by paleontology, with a climatically defined boundary.

Reevaluation of Gulf Coast Pliocene-Pleistocene Boundary: ABSTRACT

A reexamination of the sequences of planktonic foram and calcareous nannoplankton in the Plio-Pleistocene sediments beneath the Louisiana continental shelf has been undertaken to modernize correlation schemes that were established 10-20 years ago. As a consequence it can be shown that (1) a new correlation of marine micropaleontological and continental glacial events is necessary; (2) the Gulf Coast faunal events can be correlated reliably with those in the type Italian Pleistocene section and in the deep sea cores; (3) some species, the limits of whose ranges have been relied upon for isochronous boundaries (e.g., Globoquadrina altispira) appear to have persisted in some areas for a considerably longer time than in other areas; and (4) it is increasingly evident that it s invalid to correlate the Plio-Pleistocene boundary, as defined by paleontology, with a climatically defined boundary. End_of_Article - Last_Page 1698------------

Geotechnical Properties of Marine Sediments from Gulf of Mexico: ABSTRACT

Sediment cores collected from three areas of the Gulf of Mexico--the Louisiana continental shelf, the Mexican shelf-slope, and the abyssal plain--were examined to determine their geotechnical properties. As these three areas have diverse sedimentation rates ranging from rapid in proximity to the Mississippi delta to very slow on the abyssal plain, the cores were studied with the expectation that a correlation would be evident between rate of deposition and the following properties: shear strength, wet density, water content, grain-size distribution, and porosity. The cores examined from the Louisiana and Mexican shelves and the abyssal plain exhibited similar characteristics, with shear strength in the upper 10 feet of the cores averaging about 90 lbs./sq. ft. The shear-strength values of the cores taken on the Mexican slope average much higher (170 lbs./sq. ft.), with some zones having a shear strength as high as 800 lbs./sq. ft. Such a high shear strength is caused by authigenic cementation and the presence of volcanic shards. Statistically speaking, the remaining parameters measured showed less correlation between zones than did shear strength. It is assumed from this study that, although the shelf and abyssal zones are being subjected to different sedimentation rates, the processes of sedimentation are such that sediments on the Louisiana and Mexican shelves and the abyssal plain are underconsolidated as opposed to the slope sediments, which are in a normal to overconsolidated state. End_of_Article - Last_Page 606------------

Forecast of Exploration and Development of Salt-Dome Structures of Louisiana Continental Shelf: ABSTRACT

Drilling exploration of structures of the Louisiana Continental Shelf has progressed to such an extent that it appears that a reasonable prediction can be made of the number of the various types of structures that will eventually be found when development of this area has reached a stage comparable with that now existing for the onshore Miocene area of South Louisiana. Based on a study of the land Miocene area, it is estimated that a total of 540 offshore structures will be found out to water depths of 600 feet, of which 216 will be productive of gas, 124 productive of oil, and 200 productive of both oil and gas. It is estimated that, of this total of 540 structures, 81 are piercement salt domes with the major reserves trapped against the domal core, and 459 are deep-seated features which, though related to deep salt intrusion, have their major oil and gas reserves in reservoirs above the salt core. The area covered by the average deep-seated salt dome feature is approximately 9 square miles in the land Miocene area, as compared with approximately 19 square miles of structural area encompassed by the average piercement salt dome. The average gas-productive structure is substantially smaller than the average structure productive of oil, or of oil and gas. The same relationships can be anticipated offshore. It also appears reasonable to anticipate that approximately 20 per cent of the total of 24,552 square miles of offshore water bottoms underlain by potentially productive Miocene and younger sediments will be proved to be occupied by structures, restrictive parts of which will be productive of oil or gas. It is estimated that 288 structures are present in water depths of less than 100 feet, of which 200 undrilled but potentially productive structures still remain to be found. It should be remembered that many of these structures will be proved non-commercial with development drilling. In the essentially unexplored water depths from 100 feet to 600 feet, it is estimated that 252 structures potentially productive of oil or gas will be found eventually, only one of which has been drilled to July, 1961. The presence of a type of structure not common to the land Miocene area of Louisiana but associated with salt uplift and intrusion is described, and the possibility of additional occurrences of this type of prolific structure elsewhere offshore is discussed. End_of_Article - Last_Page 259------------

Engineering Characteristics of the Gulf Coast Continental Shelf

Abstract The Louisiana Continental Shelf is a submarine area extending offshore asmuch as one hundred miles. The Gulf bottom in this region varies considerablyin extent, profile and composition and consists largely of sedimentarydeposits, predominantly those of the Mississippi River. It is very young in ageological sense. Up to the present time few major structures have been erected offshore inthe Gulf and no comprehensive preliminary tests have been carried out. Resultsof pile-driving tests are of little value as actual bearing capacities farexceed the dynamic resistance to driving as measured by conventional formulas.Soils encountered are, with few exceptions, cohesive and piling consequentlydevelop their supporting power through surface friction. Because of the time required and relatively high costs, no complete loadtests have been made. The results of those tests which have been made, andinformation obtained from pulling piling in one structure, indicate that designloadings could be considerably increased, and it is contended thatcomprehensive preliminary investigations including an actual load test, combined with borings and examination of materials encountered by competentsoil experts, would effect economies in design far in excess of their cost. The Louisiana Continental Shelf - General The Louisiana continental shelf is a submarine area which extends seawardfor as great a distance as one hundred miles off the present shoreline. TheGulf bottom in this region is characterized by low slopes and its outer marginis outlined by the fifty fathom (300'Ft.) contour. South of the margin of theshelf the slopes steepen abruptly in the continental slope zone and plunge intothe deeps of the Gulf of Mexico. The engineer who is called upon to design a structure on this shelf isconcerned only with the uppermost portion to a depth generally not to exceed100 to 15? ft. This layer is very young in a geological sense, and it has thecharacteristics usually associated with infancy. A few of these are lack ofstrength, lack of uniformity, and high water content. It consists of thesedimentary deposits of the various rivers and streams entering the Gulf. Thesestreams are all heavily burdened in quantities sufficient to fill the areas attheir mouths, were it not for the fact that continual subsidence, equal orgreater in amount and acting directly opposite, prevail over the sedimentaryworkings of the streams. This subsidence has been estimated by geologists to beat the rate of at least one foot per century. Influence of Mississippi River The Mississippi River, which has been the predominant factor in theformation of practically all the Louisiana continental shelf, is one of tworivers flowing into the Gulf that have been able to build protruding deltas.The Mississippi has done so because of its enormous size and load. It depositssediments in amounts sufficient to replace and actually gain on the amount ofsubsidence. T.P. 2323