Preliminary Geologic Description S.A. Holditch & Associates SFE No. 2

Four intervals of the Travis Peak Formation were cored in the S. A. Holditch & Associates SFE No. 2 well, North Appleby field, Nacogdoches County, Texas. Core was recovered from 8,230.0 to 8,319.7 ft, 8,678.2 to 8,738.0 ft, 9,480.0 to 9,572.1 ft, and 9,806.7 to 9,942.1 ft. The top of the Travis Peak is at 8,000 ft (log depth), so the core samples are from 230 ft to 1,942 ft below the top of the formation.Bureau of Economic Geolog

The nature of iron-oxygen vacancy defect centers in PbTiO3

The iron(III) center in ferroelectric PbTiO3 together with an oxygen vacancy forms a charged defect associate, oriented along the crystallographic c-axis. Its microscopic structure has been analyzed in detail comparing results from a semi-empirical Newman superposition model analysis based on finestructure data and from calculations using density functional theory. Both methods give evidence for a substitution of Fe3+ for Ti4+ as an acceptor center. The position of the iron ion in the ferroelectric phase is found to be similar to the B-site in the paraelectric phase. Partial charge compensation is locally provided by a directly coordinated oxygen vacancy. Using high-resolution synchrotron powder diffraction, it was verified that lead titanate remains tetragonal down to 12 K, exhibiting a c/a-ratio of 1.0721.Comment: 11 pages, 5 figures, accepted in Phys. Rev.

Site Selection for Gri Cooperative Tight Gas Field Resesarch Volume 2: Geologic Characteristics of Selected Low-Permeability Gas Sandstones

Geological, engineering, and economic data on selected formations were compiled to provide a basis for siting the fourth Staged Field Experiment (SFE) for the Tight Gas Sands research program. The geologic units chosen are the Abo, Cleveland, and Frontier Formations, and the Mesaverde Group. Extrapolation potential is good for all formations except the Cleveland, whose thin deltaic package has no good analogy in other low-permeability sandstones. The Abo has the best potential for extrapolation to other low-permeability formations. The average thickness of reservoirs is about 250 ft in the Mesaverde and Abo, 160 ft in the Frontier, and 120 ft in the Cleveland. The deepest production depth varies from 4,750 ft (Abo) to 12,198 ft (Second Frontier sandstone). The estimated resource base ranges from 3 TCF (Abo) to 86 TCF (Mesaverde). Pre-stimulation production ranges from too small to measure (Cleveland, Frontier, Mesaverde) to 314 MCFD (Frontier). Post-stimulation production ranges from 3 MCFD (Mesaverde) to 12,250 MCFD (Cleveland). Permeability ranges from less than 0.0001 md (Frontier) to 1.3 md (Frontier). Natural fractures have been shown to be significant locally in the Mesaverde, but their contribution to reservoir permeability in the other formations is not well-documented.Bureau of Economic Geolog

Geology of the Lower Cretaceous Travis Peak Formation, East Texas: Characterization of a Tight Gas SandStone

Since 1982, the Gas Research Institute (GRI) Tight Gas Sands Project has supported geological investigations designed to develop knowledge necessary to efficiently produce low-permeability, gas-bearing sandstones. As part of that program, the Bureau of Economic Geology has conducted research on low-permeability sandstone in the Lower Cretaceous Travis Peak (Hosston) Formation in East Texas. The first phase of the study, which lasted from 1983 until 1986, involved extensive collection of core and production data in seven cooperative wells. Information gained from the cooperative wells, combined with geologic characterization of the Travis Peak throughout the study area, led to the drilling by GRI of three Staged Field Experiment (SFE) wells between 1986 and 1988. The SFE wells were drilled and completed by GRI specifically for the purpose of research on low-permeability gas reservoirs. This report summarizes the results of the geologic studies of the Travis Peak Formation, and it focuses on the contribution of geology to evaluation and completion of tight gas sandstone wells.Bureau of Economic Geolog

Geology of the Lower Cretaceous Travis Peak Formation, East Texas: Depositional History, Diagenesis Structure and Reservoir Engineering Implications

This report summarizes stratigraphic, petrographic, and structural studies of the Lower Cretaceous Travis Peak Formation, a low-permeability gas sandstone in East Texas, and presents reservoir engineering implications. Depositional systems in this region were interpreted from logs and cores and include (1) a braided- to meandering-fluvial system that forms the majority of the Travis Peak section; (2) deltaic deposits interbedded with the distal part of the fluvial system; (3) paralic deposits that overlie and interfinger with the deltaic and fluvial deposits near the top of the Travis Peak; and (4) shelf deposits present at the downdip extent of the formation. Petrographic studies indicate the sandstones are quartzarenites and subarkoses. Cementation by quartz, dolomite, ankerite, illite, chlorite, and reservoir bitumen have reduced porosity to less than 8 percent and permeability to less than 0.1 md throughout most of the formation. Structurally deeper sandstones are more intensely quartz cemented than are shallower sandstones and contain abundant, open natural fractures. Borehole breakouts and drilling-induced fractures in core can be used to predict horizontal stress directions and the direction of hydraulic fracture propagation. Hydraulic fractures propagate in directions subparallel to the east-northeast strike of the natural fractures; thus, hydraulically induced fractures may not intersect many natural fractures.Bureau of Economic Geolog

Mapping Kenyan grassland heights across large spatial scales with combined optical and radar satellite imagery

Grassland monitoring can be challenging because it is time-consuming and expensive to measure grass condition at large spatial scales. Remote sensing offers a time- and cost-effective method for mapping and monitoring grassland condition at both large spatial extents and fine temporal resolutions. Combinations of remotely sensed optical and radar imagery are particularly promising because together they can measure differences in moisture, structure, and reflectance among land cover types. We combined multi-date radar (PALSAR-2 and Sentinel-1) and optical (Sentinel-2) imagery with field data and visual interpretation of aerial imagery to classify land cover in the Masai Mara National Reserve, Kenya using machine learning (Random Forests). This study area comprises a diverse array of land cover types and changes over time due to seasonal changes in precipitation, seasonal movements of large herds of resident and migratory ungulates, fires, and livestock grazing. We classified twelve land cover types with user’s and producer’s accuracies ranging from 66%–100% and an overall accuracy of 86%. These methods were able to distinguish among short, medium, and tall grass cover at user’s accuracies of 83%, 82%, and 85%, respectively. By yielding a highly accurate, fine-resolution map that distinguishes among grasses of different heights, this work not only outlines a viable method for future grassland mapping efforts but also will help inform local management decisions and research in the Masai Mara National Reserve

Geology of a Stratigraphically Complex Natural Gas Play: Canyon Sandstones, Val Verde Basin, Southwest Texas

This report examines the influence of stratigraphy, diagenesis, natural fractures, and in situ stress on low-permeability, gas-bearing sandstone reservoirs of the Paleozoic Ozona and Sonora Canyon Sandstones of the Val Verde Basin, Texas. The main stratigraphic controls on the distribution and quality of Canyon Sandstone reservoirs are submarine fan depositional patterns. These patterns are revealed in regional facies and maximum sandstone maps. Siderite cement is key to good within-sandstone reservoir quality. Natural fractures are widespread in both Ozona and Sonora Canyon sandstones. They could be future targets for advanced drilling methods, and they need to be taken into account in hydraulic fracture treatment design and reservoir management.Bureau of Economic Geolog

Spatial distribution of micrometre‐scale porosity and permeability across the damage zone of a reverse‐reactivated normal fault in a tight sandstone : Insights from the Otway Basin, SE Australia

This research forms part of a PhD project supported by the Australian Research Council [Discovery Project DP160101158] and through an Australian Government Research Training Program Scholarship. Dave Healy acknowledges the support of the Natural Environment Research Council (NERC, UK) through the award NE/N003063/1 ‘Quantifying the Anisotropy of Permeability in Stressed Rock’. This study was also funded by scholarships from the Petroleum Exploration Society of Australia and the Australian Petroleum Production and Exploration Association. We thank Gordon Holm for preparing thin sections and Colin Taylor for carrying out particle size measurements and mercury injection capillary pressure analyses. Aoife McFadden and David Kelsey from Adelaide Microscopy, Braden Morgan, and Sophie Harland are acknowledged for their assistance with laboratory work. Field assistants James Hall, Rowan Hansberry, and Lachlan Furness are also gratefully acknowledged for their assistance with sample collection. Discussions with Ian Duddy on the mineralogy of the Eumeralla Formation are also greatly appreciated. This forms TRaX record 416.Peer reviewedPublisher PD

Naturally propped fractures caused by quartz cementation preserve oil reservoirs in basement rocks

MB is in receipt of a postgraduate studentship from PTDF (Nigeria). Skilled technical support was provided by M. Baron and J. Still. Two reviewers made valuable criticisms that improved the paper.Peer reviewedPostprin

Elevated blood pressures in mice lacking endothelial nitric oxide synthase

Nitric oxide produced in endothelial cells affects vascular tone. To investigate the role of endothelial nitric oxide synthase (eNOS) in blood pressure regulation, we have generated mice heterozygous (+/−) or homozygous (−/−) for disruption of the eNOS gene. Immunohistochemical staining with anti-eNOS antibodies showed reduced amounts of eNOS protein in +/− mice and absence of eNOS protein in −/− mutant mice. Male or female mice of all three eNOS genotypes were indistinguishable in general appearance and histology, except that −/− mice had lower body weights than +/+ or +/− mice. Blood pressures tended to be increased (by approximately 4 mmHg) in +/− mice compared with +/+, while −/− mice had a significant increase in pressure compared with +/+ mice (≈18 mmHg) or +/− mice (≈14 mmHg). Plasma renin concentration in the −/− mice was nearly twice that of +/+ mice, although kidney renin mRNA was modestly decreased in the −/− mice. Heart rates in the −/− mice were significantly lower than in +/− or +/+ mice. Appropriate genetic controls show that these phenotypes in F2 mice are due to the eNOS mutation and are not due to sequences that might differ between the two parental strains (129 and C57BL/6J) and are linked either to the eNOS locus or to an unlinked chromosomal region containing the renin locus. Thus eNOS is essential for maintenance of normal blood pressures and heart rates. Comparisons between the current eNOS mutant mice and previously generated inducible nitric oxide synthase mutants showed that homozygous mutants for the latter differ in having unaltered blood pressures and heart rates; both are susceptible to lipopolysaccharide-induced death