Chacko J. John

Lateral and Vertical Facies Relations of Transgressive Barrier

Identification of transgressive barrier sequences in the stratigraphic record is important because preserved barriers are potential reservoirs of petroleum. The transgressive barrier complex on the Atlantic Coast of Delaware lies at the edge of the ongoing Holocene relative rise in sea level. The Delaware coastal zone is on the northwest flank of the subsiding Baltimore Canyon Trough geosyncline of the Atlantic continental shelf. Four major variants of a transgressive barrier complex in this area are (1) a spit-beachdune complex, (2) barrier overriding a coastal marsh, (3) beach against pre-Holocene highland, and (4) a barrier-tidal delta-lagoon system which includes a linear baymouth barrier and a lobate tidal delta. Characteristic vertical sequences in each of these var ants indicate that this barrier originated farther seaward and migrated landward to its present position. Coarse sediments overlying fine sediments, generally believed to be characteristic of regressive barriers, also are present in this transgressive example. Time lines clearly diverge and cross lithologic boundaries in both transgressive and regressive barrier sedimentary units. Hence, the transgressive or regressive nature of a preserved barrier sequence cannot be positively identified on the basis of characteristic shapes of geophysical logs or sedimentary sequences. Rather, projection of barrier trends must be based on a synthesis of barrier morphology, precise identification of elements of barrier stratigraphy, knowledge of time versus stratigraphic units and lateral and vertical s quences, and an understanding of sedimentary basin tectonics.

Clinopyroxene-bearing Glass Spherules Associated with North American Microtektites

Crystallite-bearing glass spherules (<200 µm diam) are associated with North American microtektites in a Caribbean deep-sea core (RC9–58). X-ray and chemical data indicate that the crystalline phase is clinopyroxene (probably augite). The clinopyroxene-bearing spherules are similar in composition to bottle-green, high-magnesium microtektites. It appears that the clinopyroxene-bearing spherules were formed by the same event that produced the North American tektite strewnfield ∼35 m.y. ago.

MORPHOLOGY OF COASTAL BARRIERS, DELAWARE, U.S.A.

The equations describing conservation of mass, momentum and energy in a turbulent free surface flow are derived for a controle volume extending over the whole depth. The effect of the turbulent surface oscillations are discussed but neglected in the following analysis, where the equations are applied to the energy balance in a surf zone wave motion. This leads to results for the wave height variation and the velocity of propagation. The results cannot be reconciled completely with measurements and the concluding discussion is aimed at revealing how the model can be improved.A three-dimensional morphodynamic model of sequential beach changes Is presented. The model Is based on variations in breaker wave power generating a predictable sequence of beach conditions. The spectrum of beach conditions from fully eroded-dissipatlve to fully accreted reflective is characterised by ten beach-stages. Using the breaker wave power to beach-stage relationship the model Is applied to explain temporal, spatial and global variations In beach morphodynamlcs.The agents of initial damage to the dunes are water, which undermines them, and animals (including man) which damage the protective vegetation by grazing or trampling. Of these, man has recently assumed predominant local importance because of the popularity of sea-side holidays and of the land-falls of certain marine engineering works such as oil and gas pipelines and sewage outfalls. The need is therefore increasing for active dune management programmes to ensure that under these accentuated pressures, the coast retain an equilibrium comparable with that delicately balanced equilibrium which obtains naturally at a particular location.

Regional Chronostratigraphic and Depositional Hydrocarbon Trends in Offshore Louisiana State Waters

ABSTRACT Successful exploration for hydrocarbons in the Northern Gulf of Mexico basin requires a systematic understanding of hydrocarbon producing trends, sand body geometries and the geologic, engineering and reservoir parameters of the producing sands. This study forms part of the Offshore Atlas project in progress at the University of Texas at Austin, Bureau of Economic Geology, Texas, in cooperation with the U.S. Department of Interior, Minerals Management Service, and the Geological Survey of Alabama, and is aimed at achieving this goal. In this study, 26 chronozones were grouped into 12 sub-groups. The chronozones were defined on the basis of the benthic foraminiferal biostratigraphic zones and were correlated across the Gulf using well and seismic data and were projected from the Federal offshore into the State waters. The chronozones on each well log in the 22 cross sections constructed from West Cameron area eastward to the Chandeleur Sound, Breton Sound and Main Pass areas, were subdivided as applicable into four depositional groups consisting of aggradational, progradational, transgressive and submarine fan facies based primarily on SP log shapes. In the Louisiana State waters there are 92 fields containing 685 reservoirs. This includes 214 oil, 347 gas, 33 condensate and 91 combination type reservoirs. Total combined cumulative production is 1,44l,091,263 barrels of oil, 117,641,457 barrels of condensate and 11,802,821,997 thousand cubic feet of gas. Total assigned production (1977-1995) shows the progradational facies to be most productive yielding 51.69% oil, 93.84% condensate, and 77.47% gas. The aggradational facies sands produced 46.98% oil, 1.70% condensate and 15.76% gas. The submarine fan facies yielded 1.21% oil, 4.45% condensate, and 6.74% gas. Production from the transgressive facies sands was less than 0.2% of the total assigned production of oil, gas and condensate.

Determination of Storm Overwash Periodicity from Stratigraphic Relations in Delaware Coastal Barriers: ABSTRACT

Atlantic coastal barriers of Delaware are characterized by relatively thick (> 1 m) sandy washover units interbedded with thin silts and clays. The coarse-grained sediments represent overwash deposition during storm conditions, and are separated by lagoonal and marsh muds deposited during quiescent periods between storms. Washover deposits consist of fine-grained to coarse-grained, moderately sorted, negatively skewed sands. Internal sedimentary structures, consisting of lower units of small- and large-scale trough cross-bedded laminations and upper units of slightly landward-dipping parallel laminae, reflect the transition from lower to upper flow regime as storm intensity peaked. The fine-grained materials represent lagoonal and back-barrier marsh deposition, and con ist of silts and clays containing characteristic faunal and floral components. The sand unit forms a sharp contact with underlying muds, whereas the upper boundary is a gradational sand-to-mud contact as back-barrier marsh deposition reestablished on the washover-fan surface. Thickness and lateral extent of washover deposits vary depending on magnitude of wave parameters and storm tide. Large fans may extend as far as 1 km landward, and exceed 1 m in thickness. Radiometric dating of organic material in marsh and lagoon deposits permits establishment of up to four major depositional events during the past 2,700 years. Back-barrier marsh mud sequences suggest a time of stability and low storm periodicity, whereas the greater part of the barrier washover sequences suggests a higher frequenc of major storm overwash and upbuilding of the back barrier. Thus, storm-overwash periodicity may be the major determinant in establishment of lateral facies interrelations between coastal-barrier and lagoonal sequences in the stratigraphic record. End_of_Article - Last_Page 492------------

MISSING WELL LOCATIONS: AN ENVIRONMENTAL RISK ASSESSMENT AND REGULATORY PROBLEM FOR LOUISIANA

The focus of this project is to examine 48,953 well permits and create a digital database of the locations from various public records. The Basin Research Institute (BRI), Louisiana State University, in cooperation with the Louisiana Department of Natural Resources, Office of Conservation, will obtain paper records of each well permit. Using various purchased commercial oil and gas, mapping and surveying software and data management programs, (Geographix, Arcview, AutoCad Map and ProCogo) a digital latitude and longitude for each of the missing wells is being obtained. Current status of the project is that all 48,953 permits have been examined. Of that total 48,559 have been completed and digital locations have been obtained, 270 need additional information to be completed, and no determination is possible for 124 well permits. Upon completion each permit is placed in one of the following databases determined by status-Active Producers (11,450) of which 11,444 are complete or 99.99%, Shut-in Producers (2,305) of which 2,300 are complete or 99.78%, Abandoned Previous Producer (17,513) of which 17,332 are complete or 98.96%, Abandoned Dry (9,029) of which 8,883 are complete or 98.38%, Permit Expired (7,083) of which 7,040 are complete or 99.39%, and Miscellaneous Wells (1,573) of which 1,560 are complete or 99.17%. The databases will be available in both digital and hard copy format. The completed database will help Louisiana implement risk-based regulatory policies and streamline existing policies, and provide industry and the public with access to information for all phases of the oil and gas business.

ABSTRACT: Occurrence and Structural Control of Hydrocarbon Production Associated with the Baton Rouge Fault Zone, Louisiana

The Baton Rouge fault forms part of a regional east-west trending, down-to-the-basin contemporaneous fault zone known as the Baton Rouge - Tepetate Fault System. The Baton Rouge fault zone traverses the eastern to central portions of south Louisiana; the Tepetate fault zone traverses the western portion of south Louisiana. Together, these fault zones form a continuous fault system across the state that exhibits syndepositional growth in late Eocene to Oligocene time. Pronounced surface expression of the Baton Rouge fault indicates recent renewed structural fault movement. Several hydrocarbon productive fields occur along the Baton Rouge fault trend. Most of the fields are small rollover structures downthrown to the fault, however, some large rollover features and anticlinal structures have produced significant amounts of hydrocarbons. Stratigraphically trapped accumulations of hydrocarbons near, but downdip, of the Baton Rouge fault indicates some hydrocarbons migrated updip along sedimentary layers into structures along the Baton Rouge fault. However, the hydrocarbon bearing rollover and anticlinal structures could have been charged by hydrocarbon migration updip toward the fault, hydrocarbon migration along the fault as a conduit, or both. Recent studies of freshwater aquifers adjacent to the Baton Rouge fault indicate the fault is a barrier to freshwater flow, but that increased freshwater pumpage has moderated its behavior as a barrier. The fault is also recently inferred to act as a conduit for saltwater intrusion; it may play a similar dual role in hydrocarbon migration.

Abstract: Newly Defined Plio-Pleistocene Plays, Northern Gulf of Mexico: Field Characteristics and Production Statistics

ABSTRACT The offshore northern Gulf of Mexico (GOM) has recently accounted for ~13% of the oil and ~26% of the gas produced annually in the nation (Seni, et al., 1997). In 1997 and early 1998, leasing activity reached record levels in the GOM, emphasizing the increasingly important role of the region in supplying domestic energy. Of all the reservoirs in the GOM, Plio-Pleistocene reservoirs: 1) contain 55% of the total original proved reserves (sum of cumulative production and remaining proved reserves), 2) have produced 62% of the cumulative oil and condensate and 53% of the cumulative gas, and, 3) account for 67% of the remaining proved oil and condensate reserves and 45% of the remaining proved gas reserves. Of the Plio-Pleistocene strata alone, Pleistocene reservoirs contain most (66%) of the total original proved reserves. For the first time, geologic and engineering data on all 5,622 sandstone-body reservoirs in the 567 Plio-Pleistocene fields in the northern Gulf of Mexico have been synthesized into a play framework based primarily on depositional style and geologic age (Hentz, et al., 1997). Definition of 19 Plio-Pleistocene plays comprising 5 chronozones (lower and upper Pliocene; lower, middle, and upper Pleistocene) (Seni, et al., 1995) and 4 depositional styles (aggradational, progradational, submarine fan, and caprock) (Hunt and Burgess, 1995) allows comprehensive compilation and comparison of production and reserves statistics among chronozones and depositional styles in the northern GOM. Production and reserves data are derived from annually compiled records of the Minerals Management Service (Gulf of Mexico OCS Region) and the Louisiana Office of Conservation. Through 1994, Federal Outer Continental Shelf (OCS) Plio-Pleistocene reservoirs produced 63.439 trillion cubic feet (Tcf) of gas (98.8%) and 6.016 billion barrels (Bbbl) of oil and condensate (97.0%), as compared with 796.470 billion cubic feet (Bcf) of gas (1.2%) and 182.890 million barrels (MMbbl) of oil and condensate (3.0%) from fields in Louisiana Offshore State waters. Plio-Pleistocene reservoirs in Federal OCS fields have total remaining proved reserves of 15.412 Tcf of gas and 1.713 Bbbl of oil and condensate (Fig. 1). Remaining-proved-reserves data are unavailable on reservoirs in Louisiana Offshore State waters. Pleistocene reservoirs account for ~72% of the total Plio-Pleistocene gas production and ~53% of the total oil and condensate production of the offshore northern GOM. Lower Pleistocene reservoirs have the most gas (35.6%) and the greatest cumulative oil and condensate (35.8%) production. Nearly 72% of remaining proved gas reserves and ~62% of remaining proved oil and condensate reserves reside in Pleistocene strata. The lower Pleistocene leads all chronozones in gas (36.0%) and oil and condensate (31.1%) remaining proved reserves, nearly equaling the total gas (28.3%) and liquid (38.3%) reserves of the entire Pliocene succession (Fig. 2). Plio-Pleistocene gas reservoirs produce predominantly from progradational facies (72.0%), followed distantly by submarine-fan (18.2%), aggradational (9.8%), and caprock (negligible) reservoirs (Fig. 3). Remaining proved gas reserves are also highest in progradational reservoirs (54.7%), however, submarine-fan plays also have abundant gas reserves (36.8%). The apportionment of oil and condensate production by depositional style mirrors that of gas production. Progradational reservoirs have the highest cumulative liquid production (62.8%). The next-highest liquid-producing depositional style is submarine fan (19.7%). Remaining proved oil and condensate reserves are nearly equally divided between progradational (47.3%) and submarine-fan (46.1%) sandstone facies. Among the top five Plio-Pleistocene plays in terms of total original proved reserves, four are progradational and one (ranked second) is submarine fan. Discovery potential is highest in Plio-Pleistocene submarine-fan facies downdip of proved fields in the mostly unexplored deep-water (>1,000 ft) areas and at drillable depths in and between proved fields where drilling has not penetrated deeply enough to reach correlative facies. Progradational play areas are generally well explored, characterized by declining trends in yearly reservoir discoveries. Discovery potential in sandstone-dominated aggradational facies is limited primarily by the general scarcity of sealing shales. The abundance of aggradational sandstones having thin Figure 1. Histogram ranking the total of cumulative production and remaining proved reserves in billion barrels of oil equivalent (Bboe) in Plio-Pleistocene reservoirs according to jurisdiction: Federal Outer Continental Shelf (OCS) and Louisiana Offshore State waters. End_Page 543------------------------ shale intervals increases the likelihood of sandstone-against-sandstone communication across faults, thus greatly diminishing the effectiveness of faults as trapping mechanisms.