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Structural geology of the Priddy fault block adjacent to the Muenster Arch in Cooke County, Texas
No full textThe Barnett Shale and overlying units adjacent to the Muenster Arch in Cooke County, Texas, are significantly deformed. Well log and dipmeter data indicate that a west-directed reverse fault system folded and faulted the Barnett Shale and possibly Marble Falls units, and brought in rock of unknown origin. Observations indicate an additional, south-directed faulting event led to offset between wells. These features are likely related to the Late Mississippian through Late Pennsylvanian reactivation of the basement-cored faults of the Muenster Arch
Fracture analysis and mapping of the Cretaceous Boquillas Formation, Black Gap Wildlife Management Area, Brewster County, TX
No full textThe Eagle Ford Shale in south Texas is one of the most prolific unconventional hydrocarbon plays in the world (Breyer, 2016). In 2015, natural gas and oil from this field hit peak production numbers at 5,539 MMcf (million cubic feet) and 1,118,648 Bbl (barrels) per day, respectively (Texas RRC, 2016). The aim of this study is to identify any geomechanical and geochemical properties that optimize fracture connectivity within the Boquillas Formation, the West Texas Eagle Ford Shale equivalent. Here, I present a geologic map completed at 1:6000 scale of the area in and around Heath Canyon as well as data taken from four outcrop stations within Heath Canyon. Mapping was completed to understand local deformation. Fracture spacing, frequency, and vertical persistence measurements were taken in the field as well as rock strength and hardness measurements. Energy-dispersive x-ray fluorescence (ED-XRF) was used to determine the bulk elemental composition of the material and semi-quantitatively assess chemical variations throughout the outcrop. Geochemical and geomechanical data from this study suggests that fracture frequency and length/height are affected by the clay and calcite content, and, by inference, the strength of the rock.--Abstract
Chemostratigraphy, mechanical stratigraphy, and sample size: influence on micro-mechanical tests for two Barnett Shale cores, Fort Worth Basin, Texas
No full textThe Barnett Shale is one of many unconventional resources that brings a specific set of challenges and limitations, owing to the fine-grained nature of the formation. Traditional methods of describing lithologic variations and facies are limited within mudstones because subtle changes are often hard to characterize or identify without instrumentation. This study compiled a dataset of ED-XRF and unconfined compressive strength (UCS) data at three inch (7.5 cm) intervals from two Barnett Shale cores. The EOG #1 core taken from Hill County, Texas and EOG #2 core taken from Montague County, Texas. The focus of this study is to evaluate 1) chemostratigraphy and mechanical stratigraphy, 2) Bambino-measured UCS versus sample size, and 3) trends between the Dimpler and Bambino derived values related to sample composition. Results suggest these tools provide key information about composition, rock strength, and facies that cannot be measured by other traditional methods
Regional chemostratigraphy and mechanical stratigraphy of the Barnett Shale, Fort Worth Basin, Texas
No full textAlthough multiple localized chemostratigraphic and strength studies have been completed on the organic-rich Barnett Shale in the Fort Worth basin (Montgomery et al., 2005; Pollastro et al., 2007; Jarvie et al., 2007; Rowe et al., 2008; Williams et al., 2016; Taylor, 2017; Alsleben, unpublished), basin-wide correlations have not been completed. Basin-wide correlation of chemostratigraphy and mechanical stratigraphy could enhance the understanding of regional variations in chemical composition and rock competence. Therefore, this study tested multiple hypotheses to identify regional trends and correlations within the Barnett Shale, based on variations in the formations chemical makeup and rock strength. Results show three chemostratigraphic zonations that do not readily correlate to UCS divisions across the entire basin, but do correlate somewhat in the central/southern part of the basin. UCS is being controlled predominantly by clay content and secondarily by carbonate content
Unconfined compressive strength and angle of internal friction of the Wolfcamp Formation, Delaware Basin, New Mexico
No full textUnconfined Compressive Strength (UCS) in the Wolfcamp Formation of the Delaware Basin is poorly constrained. This study establishes a fine-scale hardness profile using the Bambino (L`) on a core from Lea County, NM. These data are used to create an empirical relationship of L` to triaxial UCS measurements and a fine-scale UCS curve, which is 2-3 times more detailed than log-based calculations. Pre-existing empirical relationships of log-based UCS curves are tested and found to be inaccurate resulting in the creation of new equations for log-based UCS estimates in the Wolfcamp Formation. The most accurate log curve to estimate UCS is the Gamma Ray log. Additionally, pre-existing log based AIF estimates are verified and found to be accurate enough for rock strength evaluation. This study is limited to the Wolfcamp Formation in the Delaware Basin and may not be viable for over- or underlying formations
A method for evaluating the effects of stresses and rock strength on fluid flow along the surfaces of mechanical discontinuities in low permeability rocks
No full textIntegrated geochemical, mechanical, and lithological characterization of the Marcellus Shale, Pennsylvania
No full textThe middle Devonian (392-387 Ma) Marcellus Shale is one of the primary targets for unconventional drilling in the Appalachian basin. Despite its often homogenous and fine-grained appearance, the Marcellus Shale was deposited under varying environmental conditions, which can lead to subtle differences in fabric and texture not readily identifiable by conventional low resolution sampling and analysis. This study incorporates high resolution geochemical, mechanical, and lithological characterization from two vertical cores to assess vertical and lateral heterogeneity of the Marcellus Shale in northern Appalachian basin. Detailed analysis were also performed to understand the sediment flux, paleoproductivity and paleoredox conditions during Marcellus deposition. Interpretation of the various analytical results suggests that the Marcellus Shale is vertically and laterally heterogeneous. Redox-sensitive trace elements also suggest that the Marcellus Shale was most likely deposited in predominantly anoxic deep-water conditions
Deformation in the lower Barnett Shale in the Dangelmayr-Fitzgerald fault block, Fort Worth Basin, Cook and Montague Counties, Texas
No full textThe Barnett Shale and overlying, sub-Atokan units of the Marble Falls are significantly deformed in eastern Montague and western Cooke Counties, Texas, where they meet the Muenster Arch. Well log, core, and dipmeter data indicate that at least two regional, WSW-verging, asymmetric anticlines, informally named the Sub-Mississippian Anticline and the Barnett Anticline, exist on the Cooke-Montague county border. Faults observed in this study are not equivalent to the basement-seated faults that comprise the Muenster Arch. They are, instead, likely connected to basement-seated faults through a detachment that exists within the Lower Barnett Shale. Dipmeter data indicate that movement along the basement-cored faults of the Muenster Arch occurred as late as after the deposition of the sub-Atokan Marble Falls units (Morrowan). Pennsylvanian deformation related to movement along the Muenster Arch resulted in a basinward migration of the deformation front with time
Stratigraphy Of The Ernst Member Of The Upper Cretaceous Boquillas Formation, Black Gap Wildlife Management Area, Brewster County, Texas
No full textThe time-equivalent Boquillas Formation and Eagle Ford Shale (EFS) were deposited on the South Texas Shelf in the Late Cretaceous (Cenomanian-Turonian) during a time of widespread marine transgression. The two formations consist of organic-rich shales and marls interbedded with calcareous limestones that vary laterally and vertically in thickness. The organic-rich shales and marls in the lower part of the EFS have been major targets for unconventional production in south Texas and the East Texas Basin since 2008. The goal of this study was to characterize the depositional environment of the Ernst Member in the Black Gap area of Brewster County and potentially correlate the lithological, geochemical, and mechanical data gathered with the proximal and distal Ernst Member and Eagle Ford studies. The Ernst Member of the Boquillas consists of alternating layers of low angle cross stratified to laminated grainstones, laminated argillaceous wackestones, and bentonites. The rocks were deposited below storm-wave base in a commonly anoxic/euxinic environment that contained rarely oxygenated bottom waters. Intermediate and surface-waters were commonly oxygenated and sustained life, which eventually settled as calcite and was deposited along with detrital clay material and lime-mud. Additionally, the system was influenced by bottom water currents that constantly reworked and deposited pelagic carbonate and clay material. The Ernst Member in the Black Gap area is composed of four separate chemofacies. The section can further be divided into five zones based on lithostratigraphic data paired with major and trace elemental trends. Zones A and B in this study are correlated to the organic-rich zones being produced in south Texas. Detailed correlations can be made between the Ernst Member and other Boquillas/Eagle Ford sections over moderate distances, such as 30 to 50 miles (48.3 to 80.5 km), and units in Ernst Tinaja and Hot Springs in BBNP can be correlated northeastward to the Black Gap Wildlife Management area. A large sampling interval of every six inches to a foot (15-30 cm) for obtaining XRF, spectral gamma ray (SGR), and mechanical data appears to be adequate to correlate between sections with moderate to large distances between them. Additionally, broad geochemical correlations can be made from Black Gap Wildlife Management area to the Langtry area in Val Verde County and to the northwest portion of the Maverick Basin in Maverick County
Geologic mapping and ground-penetrating radar surveys of the Valle Santo Tomas segment of the Agua Blanca fault, Baja California, Mexico
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