Academic literature on the topic 'Environmental geology – Texas – Burnet County'

The Delaware Basin of W Texas and SE New Mexico is the western subdivision of the Permian Basin and a northern extension of the Chihuahuan Desert. The major evaporite unit within the Delaware Basin is the Castile Formation, which consists of gypsum/anhydrite and is highly susceptible to dissolution and karstification. Manifestations of karst within the Castile outcrop are abundant and include sinkholes, subsidence features and caves, both epigene and hypogene in origin. Land reconnaissance surveys conducted during 2015 and 2016 documented abundant karst landforms near major thoroughfares in Culberson County, Texas. Two dimensional (2D) electrical resistivity surveys were conducted at four sites to characterize and delineate karst related hazards, both laterally and vertically, associated with the road. The electrical resistivity data were collected with a multi-electrode earth resistivity meter using a dipole-dipole array configuration. The resistivity data were then processed using EarthImager2D to produce inverted profile sections of each site. Two-dimensional electrical resistivity tomography was shown to be an effective non-invasive method in detecting solution conduits, soil filled voids, and fractured bedrock in the shallow subsurface in addition to those directly observed on the surface.

Soil properties within the Rio Grande valley near El Paso are strongly linked to the types of fluvial deposits that serve as parent material. We used four geophysical techniques (DC resistivity, ground conductivity, capacitively coupled resistivity and magnetics) to distinguish between soil units in an alfalfa field. We combined these observations with geochemical characterization and particle size analysis in order to determine how these soils and irrigation practices influence salt buildup and water availability, and thus crop growth. Soils mapped at the site were derived from crevasse splay and flood plain deposits. Results of our investigation showed that the alfalfa grew better in soils with a 1.25 m thick unit of 40-70% sand that fined into a silty-clay (<20% sand) at greater depths. Poorer growth occurred in soils where a 0.8 m thick silty-clay (<20% sand) was underlain by a less than 2 m thick sand unit (>90% sand) we interpret as an abandoned river channel. The DC resistivity, capacitively coupled resistivity and conductivity surveys were all responsive to the major grain size changes in the upper 3 meters of soil and were able to distinguish the buried river channel. The magnetics survey was not as successful at detecting the channel, but was able to characterize near-surface grain size variability and hence distinguish between the major soil units found at the site. We believe that similar geophysical techniques could be used to rapidly evaluate soil characteristics in other regions where soils are derived from fluvial parent material.

Ammonium perchlorate, a risk to human health, was used formerly to manufacture rocket fuel at the Naval Weapons Industrial Reserve Plant (NWIRP) McGregor, McLennon County, Texas. Perchlorate exists in several groundwater contaminant plumes, whose geometries were suspected to be influenced by transmissive bedrock structures. To identify these possible contaminant-transport pathways, a towed-array ground-penetrating radar (GPR) system was used to acquire 118 line-km of data across [Formula: see text] of the property. The shallow geology consists of bedrock limestone overlain by [Formula: see text] of clay soil. For the [Formula: see text] antennas used, the conductive clay limits depth penetration to less than [Formula: see text] and yields a [Formula: see text] wavelength, reducing lateral and vertical resolution. Nevertheless, GPR data resolved the top of bedrock in many areas. Linear discontinuities in bedrock were interpreted as weathered fracture zones, and linear areas of signal loss were attributed to deeper clay weathering along fracture zones. GPR-interpreted fractures have orientations corresponding to known lineament and fault trends, appear to control plume geometries, and tend to have higher hydraulic transmissivities. GPR results led to a more complete contaminant-transport model and were used to optimize the positions of monitoring wells needed to define the extent of contamination. This reduced the cost and time required for an environmental investigation at the site. GPR was helpful also in positioning remedial trenches across contaminated structures, resulting in plume containment at the property boundaries.

Summary This article presents the results of a multidisciplinary, four-dimensional (4D) (time-lapse), three-component (3C) (multicomponent) seismic study of a CO2 injection project in vacuum field, New Mexico. The ability to sense bulk rock/fluid properties with 4D, 3C seismology enables characterization of the most important transport property of a reservoir, namely, permeability. Because of the high volume resolution of the 4D, 3C seismology, we can monitor the sweep efficiency of a production process to see if reserves are bypassed by channeling around lower permeability parts of the reservoir and the rate at which the channeling occurs. In doing so, we can change production processes to sweep the reservoir more efficiently. Introduction Improving reservoir performance and enhancing hydrocarbon recovery while reducing environmental impact are critical to the future of the petroleum industry. To do this, it must be possible to characterize reservoir parameters including fluid properties and their changes with time, i.e., dynamic reservoir characterization. The objectives of our research arerepeated acquisition of a three-dimensional (3D), three-component (3C) seismic survey;demonstrate the ability of 3D, 3C, and four-dimensional (4D), 3C seismology to detect and monitor rock/fluid property change associated with a production process;incorporate geological, petrophysical, petroleum engineering, and other geophysical studies;refine the reservoir model and recommend procedures for scaling up from a pilot injection program to partial field flood to achieve maximum sweep efficiency and minimize bypassed reservoir zones;link bulk rock/fluid property variation monitored by time-lapse multicomponent (4D, 3C) seismic surveying to dynamic attributes of the reservoir including permeability, fluids, and flow characterization. Three-dimensional, 3C seismology involves seismic data acquisition in three orientations at each receiver location—two orthogonal horizontal and one vertical. When three source components are used, nine times the amount of data of a conventional P-wave 3D survey can be recorded. Horizontal components of source and receiver displacements enable shear- (S-) wave recording; this is a powerful complement to vertical P-wave recording. Three-dimensional, 3C seismic surveys provide significantly more information about the rock/fluid properties of a reservoir than can be achieved from conventional P-wave seismic surveys alone. By combining P- and S-wave recording, the seismic ability to determine rock/fluid property changes in the subsurface is increased. Seismic wave propagation includes travel time, reflectivity, and the effects of anisotropy and attenuation. In-situ stress orientation and relative magnitudes can be derived from seismic anisotropy. Rock/fluid properties, including lithology and porosity, may be obtained from comparative travel times or velocities of P and S waves. Other rock/fluid properties, including permeability, may be determined from comparative P and S anisotropy, travel time, reflectivity, and attenuation measurements. By combining P- and S-wave recording, seismic wave propagation characteristics can be transformed into reservoir parameters. Introducing time as the "fourth dimension," new time-lapse (4D), 3C seismology is a tool to monitor production processes and to determine reservoir property variations under changing conditions. Using 4D, 3C seismic monitoring as an integral part of dynamic reservoir characterization, refinements can be made to production processes to improve reservoir hydrocarbon recovery. VP/VS ratios for both the fast S1 shear component and slow S2 shear component may provide a tool for separating bulk rock changes due to fluid property variations from bulk rock changes due to effective stress variations. Changes in shear wave anisotropy may reflect varying concentrations of open fractures and low aspect ratio pore structure in both a spatial and temporal sense across the reservoir. The permeability of a formation, or the connectivity of the pore space, will be the target in 4D, 3C seismology. Refinements made to reservoir characterization techniques and their applications, now extending into the fourth dimension, are an important new area of research. Benefits of this research will include improved reservoir characterization and correlative increased hydrocarbon recovery and reduction in operating costs through improved reservoir management. Geologic Setting Since early Permian time, the general evolution of the portion of the Permian Basin which includes vacuum field is that of a progressively shallowing-upward carbonate platform. Aggrading and prograding cycles represent, respectively, the results of high stand and still stand sea levels. At the shelf edge these platform carbonates typically grade into reef-type deposits such as the Abo, Goat Seep, and Capitan formations. The San Andres is an exception; no reef-like rocks have been detected. Beyond the shelf edge, in the Delaware basin, clastic rocks, especially siliciclastics, were deposited during a lowstand sea level. Vacuum field is located on a large anticlinal structure that plunges slightly to the east-northeast. The San Andres and Grayburg formations correspond to the rim of a broad carbonate shelf province to the north and northwest, northwest shelf, and of a deeper intracratonic basin, Delaware basin, on the southeast and east.1 The overall area including the Midland basin, northern and eastern shelves, and central basin platform are part of a major restricted intracratonic basin which existed during Permian time. West Texas and southeast New Mexico were in the low latitudes throughout the late Paleozoic period, making them an ideal location for carbonate sedimentation. As a consequence of this tropical environment, broad carbonate shelves were established on the margins of the Delaware and Midland basins.2

The Eagle Ford Shale in southern Texas remains one of the most productive oil and gas regions in the US. Like the Permian Basin and Bakken Shale, ubiquitous natural gas flaring serves as an uncertain source of trace gas emissions within the Eagle Ford. A lack of ambient air quality data, especially in the western shale, impedes a thorough understanding of trace gas emissions within the shale and the subsequent local/regional air quality impacts. Meteorological and trace gas instrumentation was deployed to Shape Ranch in southwestern Dimmit County, near the US/Mexico border, from April to November of 2015. Mixing ratios of CO, NOx, O3, and VOCs did not exceed ambient air quality standards and were generally lower than mixing ratios measured in US cities, with the exception of alkanes. A non-negative matrix factorization demonstrated the dominance of oil and gas-sector emission sources in local trace gas variability, with combustion processes and transport of continental air also present. An analysis of NOx/CO and NOx/CO2 ratios during periods of O3 titration, identified by the ambient NOx/O3 ratio, suggested that combustion and biospheric sources contributed to emissions of NOx, CO, and CO2. In-plume NOx/CO2 ratios indicated relatively low-temperature combustion sources, with median NOx/CO2 ratios close to that expected for natural gas flaring (0.54 ppb/ppm), and much lower than emission ratios for internal combustion engines (>10 ppb/ppm). However, the NOx/CO2 ratio within these plumes exhibited a large variability, spanning more than an order of magnitude. Future research should focus on improving flaring emission factors and flaring volume estimates such that their air quality impacts can be better understood.

Eighty-nine caves and sinkholes were investigated in the Edwards Aquifer recharge zone in Bexar County, Texas. The study examined their hydrogeologic and topographic origins and distribution, relationships to major fracture traces, quantity of recharge into the aquifer and degree of sensitivity towards degradation of the aquifer’s water quality. Groundwater traces were attempted to determine aquifer flow routes, time of groundwater travel, groundwater volume within conduits, and the aquifer’s capacity for dilution and dispersion of recharged contaminants. Trends in water quality were examined to quantify the volume and variety of contaminants recharged into the aquifer and to determine the effects of urbanization upon the Edwards Aquifer. The Edwards recharge zone was hydrogeologically assessed to rate the sensitivity of its areas. Socio-political impacts on recharge zone development were also examined. Based on the results of the above outlined research method, the conclusions of this investigation are that caves and sinkholes contribute substantial recharge into the Edwards Aquifer, rapidly transmit that recharge to the aquifer and are sensitive sites for potential contamination. The entire recharge zone was determined to be very sensitive to contamination. No significant differences were found between areas within the recharge zone to scale their degree of sensitivity. Major conduit flow networks were found to exist within the aquifer and their groundwater flow paths could be traced. Urban development of the Edwards recharge zone was shown to decrease the volume of recharge and degrade the aquifer’s water quality. No significant detrimental effects on the aquifer were observed. The volume of diminished recharge and the concentration of recharged contaminants that were necessary to produce significant adverse effects on the aquifer were not determined due to lack of precipitation during the study period and inconclusive groundwater tracings. It was recommended that further development of the recharge zone be suspended until the effects of urbanization are quantified.