Browsing by Subject "Petroleum -- Geology -- Texas"

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Depositional systems in the Paluxy formation (Lower Cretaceous), northeast Texas-oil, gas and groundwater resources
(University of Texas at Austin. Bureau of Economic Geology, 1977) Caughey, Charles A.
The Paluxy Formation is a stratigraphic unit which is composed of sandstone and shale and extends across the northern part of the East Texas embayment. Paluxy deposits were derived from sedimentary rocks to the north, and they accumulated in shoreface and coastal plain environments associated with an irregular southward regression of the shoreline. Preserved in the sedimentary mass are three major depositional systems: a centrally located delta system, a fluvial system in the north, and a strandplain system in the west. The delta system is wave dominated, composed largely of marine-influenced sediments aligned along depositional strike. Sand isolith maxima, associated with stacked coastal barrier deposits, outline the cuspate shape of the delta system. Two principal delta lobes are recognizable; these are centered in Hunt and in Wood Counties. The fluvial system consists of a broad, sandy meanderbelt facies which thins northward into discrete channel complexes separated by floodbasin deposits. The strandplain system blankets the western embayment margin with coalescent beach ridge and associated shoreface and coastal lake deposits. Strandplain sands provide small to moderate quantities of groundwater that are generally suitable for uses other than irrigation. Fluvial system deposits furnish local areas with water for irrigation and for domestic and municipal supply. Major oil and gas accumulations occur in deltaic coastal barrier and fluvial meanderbelt facies.
Depositional systems in the Wilcox Group of Texas and their relationship to occurrence of oil and gas
(University of Texas at Austin. Bureau of Economic Geology, 1967) Fisher, W. L. (William Lawrence), 1932-; McGowen, J. H.
Regional investigation of the lower part of the Wilcox Group in Texas in outcrop and subsurface indicates seven principal depositional systems. These include: (1) Mt. Pleasant Fluvial System developed updip and in outcrop north of the Colorado River;(2) Rockdale Delta System, present primarily in subsurface, chiefly between the Guadalupe and Sabine Rivers; (3) Pendleton Lagoon-Bay System in outcrop and subsurface largely on the southern flank of the Sabine Uplift; (4) San Marcos Strandplain-Bay System, occurring in outcrop and subsurface mainly on the San Marcos Arch; (5) Cotulla Barrier Bar System in subsurface of South Texas; (6) Indio Bay-Lagoon System developed updip and in outcrop of South Texas; and (7) South Texas Shelf System, an extensive system entirely within subsurface of South Texas. The Rockdale Delta System, consisting of large lobate wedges of muds, sands, and carbonaceous deposits, is the thickest and most extensive of the lower Wilcox depositional systems. It grades updip to the thinner terrigenous facies of the Mt. Pleasant Fluvial System. Deposits of the Rockdale Delta System were the source of sediments redistributed by marine processes and deposited in laterally adjacent marine systems. Delineation of depositional systems and, more specifically, delineation of component facies of the various systems, permits establishment of regional oil and gas trends which show relationship of producing fields and distribution of potentially producing trends.
Genesis and emplacement of oil in the San Andres formation: northern shelf of the Midland Basin, Texas
(University of Texas at Austin. Bureau of Economic Geology, 1982) Ramondetta, Paul J.
San Andres oil constitutes more than 80 percent of the total production from the Northern Shelf of the Midland Basin, Texas. The San Andres and Clear Fork carbonate rocks of the Northern Shelf contain sufficient amounts of lipid-rich organic material to rank them as potential petroleum source beds. Organic maturation of these rocks, as revealed from vitrinite reflectance and kerogen color, however, is not sufficient to have initiated catagenesis. Therefore, oil within Northern Shelf reservoirs was derived mostly from other sources. San Andres oils have a common source, as evidenced by their remarkably uniform composition, which is revealed in liquid and gas chromatography, and Bartlesville Energy Technology Center (BETC) distillate analyses. Wolfcampian basinal clastics and dark argillaceous limestones of the northern Midland Basin are the most likely source rocks for this oil. Vertical expulsion of basinal oil through fractures into overlying shelf and shelf-margin carbonates has occurred along the Lower Permian Abo Reef trend. This reef hingeline is a narrow belt of shelf-margin buttresses ranging in age from Strawn to Clear Fork. The trapping mechanism in the Northern Shelf is a combination of structural and facies control. Good reservoir conditions exist in San Andres strata that are draped and subsequently fractured over the subjacent shelf-margin buttress. Such fracturing should have enhanced conditions for development of secondary porosity during periods of subaerial exposure. Above the Abo Reef trend, a thick porous zone exists in the lower San Andres and upper Clear Fork Formations; shelfward, this porous zone grades into discrete porous layers resulting from cyclic sedimentation in shallow inner-shelf and sabkha environments. These Upper Permian carbonates tend to lose porosity in a northward (updip) direction, where conditions were more evaporitic. This updip change from porous to nonporous facies provides the porosity pinch-out in the vast Levelland - Slaughter - Cato trend of Texas and eastern New Mexico. Late Cretaceous uplift in New Mexico exposed Permian strata, initiating a west-to-east flow of relatively fresh ground water. Passage of this meteoric water through San Andres and Clear Fork reservoirs caused downdip degradation and flushing of the oil. As a result of this ground-water movement, oil/water contacts tilt downdip 0.3 to 0.5, and oil production is slightly offset downdip from local structural highs. The San Andres and Clear Fork oil was degraded by anaerobic sulfate reducing bacteria, which resulted in an enrichment of sulfur and light aromatics and a slight depletion of saturated hydrocarbons. This biodegradation progressively increases updip, as evidenced by higher sulfur contents and lower API gravity.
Stuart City trend, Lower Cretaceous, south Texas : a carbonate shelf-margin model for hydrocarbon exploration
(University of Texas at Austin. Bureau of Economic Geology, 1974) Bebout, Don G.
Lower Cretaceous shallow-water carbonates accumulated on a broad shelf which completely encircled the Gulf of Mexico. Biogenic growth climaxed along the basinward edge, or shelf margin, where a complex of reefs, banks, bars, and islands developed. The sediments reached a total thickness of 2,000 to 2,500 feet; numerous deep wells ranging in total depth from 11,000 to 20,000 feet have resulted in the discovery of a few marginally productive gas fields. The objectives of this study are: (1) to describe the depositional facies and environments present along this trend in order to provide a model for further hydrocarbon exploration along the Stuart City Trend and also in the deeper Sligo Trend, and (2) to identify diagenetic processes which relate to porosity distribution and might lead to the discovery of zones of higher porosity elsewhere along the trend.
The Ellenburger group of central Texas
(University of Texas at Austin, 1948) Cloud, Preston, 1912-1991