East Texas Basin

Dutton S. P. and Diggs T. N. (1992) Evolution of porosity and permeability in the Lower Cretaceous Travis Peak Formation, East Texas Basin. Am. Assoc. Petrol. Geologists Bull. 76, 252-269. 

To address these problems, this paper presents a mass balance technique specifically developed for evaluating the resource-in-place potential of basin-centred gas prospects. This paper begins with a general overview of basin-centred gas systems (BCGS), including a summary of common attributes identified from a literature survey. A derivation of the mass balance technique and an explanation of its elements foUow this summary. Application of the technique is illustrated with an example from the Bossier tight gas sand play in the East Texas Basin located in eastern Texas, USA. Uncertainty in resource-in-place estimates are quantified by incorporating a Monte Carlo simulation technique with the mass balance computations. 

Fig. 2. Stratigraphic column for the Bossier Sands, East Texas Basin (Montgomery 2000).

The Bossier shale is not only the basal formation for much of the Cotton VaUey Group, but is also interbedded with isolated sands throughout most of eastern Texas and northwestern Louisiana. These shales are typically black, organic-rich, calcareous, fossiliferous, marine deposits which are the primary source rock for much of the entire Upper Jurassic and Lower Cretaceous vertical section. Thinner shale intervals in the western part of the basin thicken to the east correlative to general depositional patterns in the East Texas Basin. Source rock quality is generally poorer in the western and northwestern parts of the basin, but improves significantly easterly towards the basin centre. From west to east, the near-shore sand and low-stand fan deposits are usually completely encased in the marine Bossier shale. 

Fig. 4. Vertical distribution of present-day Bossier shale TOC values taken from wells located in the northwestern, central and southeastern areas of the East Texas Basin. Note the TOC distribution mimics the fluvial-deltaic progradation of sediments NW-SE.

Fig. 5. Present-day kerogen type and quality of Bossier shales in the East Texas Basin range from type II to type III.

Fig. 8. Variation of vitrinite reflectance with depth in the East Texas Basin.

Bossier sands in this area and throughout the East Texas Basin also exhibit abnormally high temperature gradients. Bottom-hole temperatures range from 280 to 325 °F at depths ranging from 12 500 to 13 500 ft. This corresponds to temperature gradients of 2.2 to 2.4 °F per 100 ft of depth. 

This section illustrates application of the mass balance technique for two exploration prospects in the East Texas Basin. Gas volumes were computed using both the conventional reservoir engineering and mass balance approaches. Furthermore, uncertainty was incorporated into the calculations with a Monte Carlo simulation technique that generates probabilistic distributions of gas volumes. 

Evaluations of two Bossier sand exploration prospects are presented to illustrate the calculation techniques. Although these two prospects were both located in the deeper parts of the basin, several hundred miles separate them. Exploration prospect number one is situated closer to the shelf area, while exploration prospect number two is located closer to the centre of the East Texas Basin. Histograms of Pjo, P50 and P90 values for gas volumes computed using both mass balance and conventional reservoir engineering approaches are shown for comparison. 

Montgomery, S. 2000. East Texas Basin Bossier gas play. In Anderson, J. (ed.) Petroleum Frontiers. IHS Energy Group, Englewood, Colorado, 1-60. 

Westcott, W. a. Hood, W. C. 1994. Hydrocarbon generation and migration routes in East Texas Basin. American Association of Petroleum Geologists Bulletin, 78(2), 287-307. 

Resources. Near-surface lignite is defined as that under less than 60 m. of cover and deep-basin, under more than 60 m. of cover. Near-surface resources are set at 21.2 billion metric tons (O. These resources occur primarily in the Wilcox (71%) and secondarily in the Jackson (22%) and Yegua (7%). Geographically over 90% of the resources are found north of the Colorado River or in east Texas (Figure 2). 

Mineral matter. Guven and Lee (11) have performed a characterization of the mineral matter found in several deep-basin lignite seams. Using core samples from Shelby, Nacogdoches, Panola, and Rusk Counties in east Texas (Wilcox Group), mineral matter has been processed using low temperature ashing (LTA) procedures. 

Tewalt and others have extensively analyzed 85 east Texas, deep-basin lignite samples collected from 18 different seams and five stratigraphic horizons in the Wilcox Group (14). In the Sabine Uplift area, among the trace elements of greatest environmental and health concern in coal (As, Pb, Se, B, Hg, Cd, and Mo), only the mean of Se (10.2 ppm) exceeds that of the average for U.S. lignite (5.3 ppm), whereas As is less (3.4 vs. 

Hydrogeologic studies prove that natural dissolution of bedded salt occurs at shallow depths in many parts of the Permian Basin of the southwestern U.S.A. This is especially well-documented on the east side of the basin in study areas on the Cimarron River and Elm Fork in western Oklahoma, and on the Red River in the southeastern part of the Texas Panhandle. Four requirements for salt dissolution are (1) a deposit of salt (2) a supply of water unsaturated with respect to NaCl (3) an outlet for removal of brine and... 

By 1970, in the wake of efforts to capitalize on the newly realized medicinal value of podophyllotoxin for Western medicine, more than 130 tons of Podophyllum rhizomes were needed in the US annually to satisfy the demand for the compound [6]. This plant material was wild-harvested from the understory of oak and hickory forests of the eastern and central US. In 1974, mayapple was considered a common plant with a natural habitat extending from South Carolina to Maine along the Atlantic coast in the East, to eastern Texas, Oklahoma, and Kansas beyond the Mississippi basin in the West, and as far North as Lake Michigan [6]. Today, mayapple is commonly seen along roadsides and can still be abundantly found in other readily accessible areas within its natural range. Several... 

Dutton, S. P., Flanders, W. A. Barton, M. D. 2003. Reservoir characterization of a Permian deepwater sandstone. East Ford field, Delaware Basin, Texas. American Association of Petroleum Geologists Bulletin, 87, 609-627. 

Environmental Science Program, College of Arts and Science, The University of Texas of the Permian Basin, 4901 East University, Odessa, TX 79762, USA... 

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