Western Gulf Basin Research Articles

A reconnaissance analysis of groundwater quality in the Eagle Ford shale region reveals two distinct bromide/chloride populations

The extraction of oil and natural gas from unconventional shale formations has prompted a series of investigations to examine the quality of the groundwater in the overlying aquifers. Here we present a reconnaissance analysis of groundwater quality in the Eagle Ford region of southern Texas. These data reveal two distinct sample populations that are differentiable by bromide/chloride ratios. Elevated levels of fluoride, nitrate, sulfate, various metal ions, and the detection of exotic volatile organic compounds highlight a high bromide group of samples, which is geographically clustered, while encompassing multiple hydrogeological strata. Samples with bromide/chloride ratios representative of connate water displayed elevated levels of total organic carbon, while revealing the detection of alcohols and chlorinated compounds. These findings suggest that groundwater quality in the Western Gulf Basin is, for the most part, controlled by a series of natural processes; however, there is also evidence of episodic contamination events potentially attributed to unconventional oil and gas development or other anthropogenic activities. Collectively, this characterization of natural groundwater constituents and exogenous compounds will guide targeted remediation efforts and provides insight for agricultural entities, industrial operators, and rural communities that rely on groundwater in southern Texas.

Tight Resources, Promising Economics: The Permian Basin Continues Yielding Liquid Riches

Permian Basin There is no doubt that the 86,000-sq-mile Permian Basin, encompassing 52 counties in west Texas and eastern New Mexico, is experiencing a renaissance in drilling activity. According to the Railroad Commission of Texas (RRC), the Texas Permian Basin rig count climbed from 129 in 2005 to 355 in 2011, sustaining a dip to 103 in 2009 with no drop in crude oil production. Total Permian Basin rig count climbed to 500 in May 2012, according to a US Energy Information Administration (EIA) report, and as of late December 2012, stood at 454. The number of drilling permits issued by the RRC has exhibited a similar rise, from 4,459 in 2005, with a downdip to 3,369 in 2009 and then a steep climb to 9,347 in 2011. The price of natural gas remains depressed in the US, largely because of a glut due to a rush to exploit very tight gas resources in shale plays such as the Marcellus, Eagle Ford, Barnett, Haynesville-Bossier, Fayetteville, Woodford, and Bakken. A trend over the past few years has therefore been building towards a focus on liquids-rich plays. As a result, US production of crude oil is reaching levels not seen in 15 years, at approximately 2.1 billion bbl/year as of September 2012, according to the US Department of Energy’s (DOE) EIA. The US now produces an average of 6.41 million BOPD, a 14% increase from 2011, according to a December 2012 DOE report—around 50% of the crude oil it consumes. The two US states emerging as yielding the greatest amount of liquids are North Dakota (the Bakken) and Texas (Permian Basin and Eagle Ford). From September 2011 through September 2012, Texas onshore crude oil production increased by more than 500,000 BOPD, due to increases in Eagle Ford and Permian Basin production. The Permian Basin now accounts for more than 18% of domestic US crude oil supply. It has more than 400 active drilling rigs, by far the most of any US basin, that are drilling a large number of wells very quickly. The EIA estimates (Fig. 1) that crude oil production from the Permian Basin surpassed 1.25 million B/D in November 2012, 33% greater than the estimated 0.93 million B/D in the Western Gulf basin and 45% greater than the 0.86 million B/D in the Williston basin.

Deep-Current Variability near the Sigsbee Escarpment in the Gulf of Mexico

Abstract Observations of deep currents, from a closely spaced array deployed at the base of the Sigsbee Escarpment, south of the Mississippi Delta, are dominated by energetic, short-period (∼10 days) topographic Rossby waves. Over a 2-yr interval, distinct trains of waves occurred, with differing characteristic periods, wavelengths, and horizontal energy distribution, usually initiated with a burst of large-amplitude current fluctuations that slowly decay over the next 2–3 months. Two of the wave trains were associated with the shedding and westward passage of major Loop Current anticyclones; however, one event occurred when upper-layer currents were quiescent. This latter wave train showed that bottom-trapped topographic wave motions can be traced to within 300 m of the surface in a 2000-m water column. Ray tracing showed that a likely source region of the short-period waves was the west side of an extended Loop Current. The data and ray paths suggest that, through refraction and reflection, the steep escarpment keeps the energetic waves confined to the deep water. These mechanisms help to explain why short-period fluctuations are not observed farther west in the central and western gulf basin.

Deltaic Sedimentation, Salt Mobilization, and Growth Faulting in Gulf Coast Basin: ABSTRACT

Regional facies mapping and analysis of thick, terrigenous wedges, and mapping of principal structural features (salt intrusion and growth faulting) indicate a direct relation between sedimentation and tectonics in the western Gulf basin. Proximal parts of clastic wedges infilling the basin consist of paralic, mainly deltaic, depositional systems; distal parts are made up largely of deep-water, continental-slope deposits. Two kinds of delta systems are characteristic: (1) high-constructive deltas marked by rapid, large-volume deposition; and (2) high-destructive deltas with large sand content and slower rates of accumulation. Distribution of 4 major high-constructive delta systems and associated continental-slope systems is coincident with 4 major salt-diapir fields (including about 90% of the domal salt structures of the basin). Mobilization of deep seated, bedded salt occurred by lateral migration to interdeltaic areas and by distal migration, establishing diapir fields fronting major delta systems and coincident with slope systems. Salt mobilization related to strike-depositional (barrier bar and strandplain) systems was generally as broad salt ridges rather than domes. In high-constructive deltas, growth faulting is facies coincident, forming at the boundary of delta-front sands and thick prodelta muds. As with salt mobilization, the principal tectonic grain of growth faulting developed in connection with the 4 major episodes of high-constructive wedges in the offlap filling of the basin, rejuvenating growth faulting and salt mobilization initiated by the high constructive deltas. Accordingly, direct facies correlation in distribution of growth faulting and salt mobilization occurred. End_of_Article - Last_Page 779------------

Possible Future Petroleum Provinces of United States Western Gulf Basin--Pre-Jurassic: ABSTRACT

In the western Gulf basin, the pre-Jurassic section can be subdivided into (1) foreland Paleozoic strata (Black Warrior basin), (2) orogenic geosynclinal facies (Ouachita tectonic belt), (3) late-orogenic, late Paleozoic rocks, and (4) post-orogenic, Late Triassic strata. A good potential for future petroleum provinces of economic interest can be recognized in the Black Warrior basin, and on the Gulf of Mexico side of the Ouachita tectonic belt, in late-orogenic, late Paleozoic strata. A remote possibility is recognized for the presence of commercial accumulations of hydrocarbon in sub-thrust lower Paleozoic foreland carbonates beneath the interior part of the Ouachita fold belt. The hydrocarbon potential of geosynclinal sediments of the Ouachita tectonic belt, and of the post-orogenic Triassic section, is considered to be negligible. The Black Warrior basin of Mississippi and Alabama contains a thick section of Paleozoic foreland rock. Although production dates back to 1909 and hydrocarbon shows have been numerous, the proved reserves are insignificant. The deep structural configuration has been difficult to map, and this has deterred deep drilling. The basin tectonics should be comparable to those of other foreland basins, in which large, buried, normal faults are characteristic. Improved seismic techniques should reveal similar anomalies in the Black Warrior basin. Large hydrocarbon accumulations may ultimately be found in deep fault traps in lower Paleozoic carbonates, and such prospects are sparsely tested. There is no production from pre-Jurassic rocks gulfward from the Ouachita front. However, exploration of this section has been quite limited, mainly because of the absence of attractive objectives. Most wells drilled below the Jurassic have found either tight, highly deformed, geosynclinal facies of the Paleozoic Ouachita system, or redbeds and igneous rocks of the Late Triassic Eagle Mills Formation. Since 1960 a few highly significant, but unpublicized, wildcats have penetrated relatively undeformed, very fossiliferous, shallow-water shelf carbonates and clastics of Pennsylvanian age beneath the coastal plain. These strata, identified from fusulinids as Desmoinesian, are present on the Gulf of Mexico side of the Ouachita fold belt in wells drilled in northeast Texas and southwest Arkansas. Commercial porosities have been found in both sandstones and carbonates. Only fragmentary data are available, but the mere presence of these strata suggests that a potentially large, virtually unexplored, petroleum province may be present in late Paleozoic rocks of the Gulf coastal plain. End_Page 1792------------------------------ A recent 20,000-ft test in Texas penetrated thick lower Paleozoic shelf carbonates on a large seismic anomaly beneath the interior zone of the Ouachita system. Although the objective carbonates were metamorphosed there, the possibility of finding favorable reservoir rock elsewhere in this trend is not necessarily eliminated. End_of_Article - Last_Page 1793------------

Possible Future Petroleum Provinces of United States Western Gulf Basin--Pleistocene: ABSTRACT

Hydrocarbons in sediments of Pleistocene age have been found in 56 fields located mainly offshore from Louisiana. The Pleistocene section of the western Gulf basin has potential for significant additional reserves of hydrocarbons. The sequence consists of 3 gross depositional facies, in ascending order, (1) deep-water bathyal sediments, (2) neritic sediments, and (3) continental deposits. The maximum thickness of the Pleistocene exceeds 10,000 ft near the outer edge of the continental shelf in the western Gulf basin. The lithologic characteristics, facies, and types of traps in which the accumulations are present are similar to those of the underlying Pliocene and Miocene beds, which contain major reserves. The greatest potential is in an area of 15,000 sq mi on the outer continental shelf offshore from Louisiana and Texas. In this area, the overall objective section, the neritic interbedded sandstone and shale facies, is from 3,000 ft to more than 8,000 ft thick. Approximately 1/3 (4,300 sq mi) of this area is in an early stage of development, and 2/3 (10,700 sq mi) is unexplored. Most of the reserves found to date are in the continental and neritic facies of the lower Pleistocene. The area of greatest potential is indicated by several factors. Potential source and reservoir rocks of the Pleistocene neritic facies are similar to those of the older, highly productive Tertiary section. Structural and stratigraphic conditions favoring the entrapment of oil occur as commonly in the most favorable Pleistocene area as in nearby areas of prolific Tertiary fields. The area of favorable stratigraphy on the outer continental shelf is underlain by many diapiric structures. Significant discoveries from marine Pleistocene sediments in recent years afford direct evidence that the section is a major objective for future exploration. In the past, this section as a potential source of hydrocarbons has been downgraded by some workers because of its relatively young age. Drilling and producing capabilities are now sufficiently advanced to permit economical operations over most of the continental shelf. However, major hydrocarbon reserves are required to justify the extremely high operating expenses in the deep-water area. The continental slope of the Gulf of Mexico offshore from Texas and Louisiana is also underlain by a large volume of Pleistocene sediments, but its potential cannot be assessed at our current state of knowledge. End_of_Article - Last_Page 1789------------

Possible Future Petroleum Provinces of Western Gulf Basin: ABSTRACT

A task force of industry geologists working in Region 6, Western Gulf basin, for the National Petroleum Council study, Possible Future Petroleum Provinces of the United States, has attempted to answer whether additional significant crude oil reserves will be added in the Western Gulf basin. The potential of non-producing areas is stressed, however, possible extensions to producing trends also are analyzed from a geologic and production-controls standpoint. The thoughts and ideas from eight industry papers covering the Western Gulf basin are summarized. End_of_Article - Last_Page 2040------------