Lithofacies and stratigraphy of a complete Woodford Shale outcrop section in South Central Oklahoma: Geologic considerations for the evaluation of unconventional shale reservoirs

2018 ◽  
Vol 6 (1) ◽  
pp. SC15-SC27 ◽  
Author(s):  
Henry Galvis ◽  
Daniela Becerra ◽  
Roger Slatt
Keyword(s):  
High Frequency ◽  
Local Source ◽  
Woodford Shale ◽  
Quartz Content ◽  
Potential Target ◽  
South Central ◽  
Lower Member ◽  
Bed Thickness ◽  
Shale Reservoirs ◽  
Multiple Scenarios

We have developed a detailed rock-based documentation of a previously undescribed Woodford Shale outcrop in South Central Oklahoma. The complete exposed section provided the opportunity to investigate lithologic attributes across the complete Woodford Shale thickness, as well as on its under- and overlying formational contacts. Within the Woodford Shale strata, seven lithofacies were recognized honoring textural and compositional attributes, and they were grouped based on their weathering response into soft (incompetent) and hard (competent) beds. Internally, across the Woodford interval, there is an overall upward increase in quartz content, represented by higher proportions of siliceous shales and chert around the middle and upper members, whereas the lower member is mostly dominated by organic and clay-rich shales interbedded with minor proportions of cherty beds. However, most notable was the rhythmic cyclicity between hard (brittle) and soft (ductile) lithofacies throughout the Woodford, from which systematic measurements of bed thickness and soft-to-hard ratios are examined to illustrate multiple scenarios of stratigraphic anisotropy. The geologic assessment of reservoir quality was assessed using the vertical arrangement of lithofacies, from which we hypothesized that potential target zones are interpreted to be composed by high-frequency interbeddings of organic-rich “soft” beds (acting as a local source) and “hard” brittle beds (acting as more frackable or fractured rocks). According to this model and the vertical stratigraphy, a potential target zone is interpreted to lie in between the upper half of the middle Woodford and lower half of the upper Woodford member, where the soft-to-hard ratio is approximately 50/50 and the beds are thinner.

High-resolution stratigraphic characterization of natural fracture attributes in the Woodford Shale, Arbuckle Wilderness and US-77D Outcrops, Murray County, Oklahoma

2018 ◽  
Vol 6 (1) ◽  
pp. SC29-SC41 ◽  
Author(s):  
Sayantan Ghosh ◽  
John N. Hooker ◽  
Caleb P. Bontempi ◽  
Roger M. Slatt
Keyword(s):  
Natural Fracture ◽  
Fracture Aperture ◽  
Aperture Size ◽  
Fracture Density ◽  
Area Formula ◽  
Woodford Shale ◽  
Fracture Spacing ◽  
Spacing Ratio ◽  
Fracture Intensity ◽  
Bed Thickness

Natural fracture aperture-size, spacing, and stratigraphic variation in fracture density are factors determining the fluid-flow capacity of low-permeability formations. In this study, several facies were identified in a Woodford Shale complete section. The section was divided into four broad stratigraphic zones based on interbedding of similar facies. Average thicknesses and percentages of brittle and ductile beds in each stratigraphic foot were recorded. Also, five fracture sets were identified. These sets were split into two groups based on their trace exposures. Fracture linear intensity (number of fractures normalized to the scanline length [[Formula: see text]]) values were quantified for brittle and ductile beds. Individual fracture intensity-bed thickness linear equations were derived. These equations, along with the average bed thickness and percentage of brittle and ductile lithologies in each stratigraphic foot, were used to construct a fracture areal density (number of fracture traces normalized to the trace exposure area [[Formula: see text]]) profile. Finally, the fracture opening-displacement size variations, clustering tendencies, and fracture saturation were quantified. Fracture intensity-bed thickness equations predict approximately 1.5–3 times more fractures in the brittle beds compared with ductile beds at any given bed thickness. Parts of zone 2 and almost entire zone 3, located in the upper and middle Woodford, respectively, have high fracture densities and are situated within relatively organic-rich (high-GR) intervals. These intervals may be suitable horizontal well landing targets. All observed fracture cement exhibit a lack of crack-seal texture. Characteristic aperture-size distributions exist, with most apertures in the 0.05–1 mm (0.00016–0.0032 ft) range. In the chert beds, fracture cement is primarily bitumen or silica or both. Fractures in dolomite beds primarily have calcite cement. The average fracture spacing indices (i.e., bed thickness-fracture spacing ratio) in brittle and ductile beds were determined to be 2 and 1.2, respectively. Uniform fracture spacing was observed along all scanlines in the studied beds.

A high frequency of structural chromosome abnormalities in a south central texas cytogenetics laboratory

1984 ◽  
Vol 19 (2) ◽  
pp. 347-358 ◽  
Author(s):  
Robert S. Young ◽  
Kathryn L. Hansen ◽  
Steven D. Shapiro ◽  
Ronald J. Jorgenson
Keyword(s):  
High Frequency ◽  
Chromosome Abnormalities ◽  
South Central ◽  
Structural Chromosome ◽  
Central Texas

scholarly journals The effect of a local source on the composition of precipitation in south-central Maine

1976 ◽  
Vol 6 (2-4) ◽  
pp. 375-384 ◽  
Author(s):  
Scott D. Boyce ◽  
Samuel S. Butchert
Keyword(s):  
Local Source ◽  
South Central

Conodonts and the Devonian–Carboniferous boundary in the upper Woodford Shale, Arbuckle Mountains, south-central Oklahoma

1992 ◽  
Vol 66 (2) ◽  
pp. 293-311 ◽  
Author(s):  
D. Jeffrey Over
Keyword(s):  
Early Carboniferous ◽  
Black Shales ◽  
Energy Conditions ◽  
Woodford Shale ◽  
Lower Paleozoic ◽  
Lower Carboniferous ◽  
South Central ◽  
Water Oxygen ◽  
First Occurrence ◽  
Arbuckle Mountains

The Woodford Shale of south-central Oklahoma was deposited in an offshore, quiet-water, oxygen-poor setting on the southern margin of North America in assocation with other dark organic-rich shales of the Upper Devonian–Lower Carboniferous black-shale facies. The basal Woodford was deposited unconformably over lower Paleozoic carbonate strata as a south-to-north transgressive unit during the Frasnian and early Famennian. Black shales and cherts lie directly above the basal beds.Phosphatic shales in the upper Woodford contain a conodont succession characterized by three distinct environmentally controlled faunas. The lower fauna is characterized by Palmatolepis gracilis ssp., Branmehla inornata, Bispathodus stabilis, and Pseudopolygnathus marburgensis trigonicus, indicative of the Late Devonian Lower expansa Zone to Upper praesulcata Zone. The middle fauna, which spans the Devonian–Carboniferous (D/C) boundary, is characterized by Polygnathus communis communis and species of Protognathodus. On the Lawrence uplift the D/C boundary is disconformable, as indicated by the absence of Protognathodus kockeli before the first occurrence of Siphonodella sulcata. Light-colored phosphate laminae and beds, indicative of erosion and nondeposition, and a change in biofacies from an offshore palmatolepid–bispathodid fauna to a more nearshore, palmatolepid–polygnathid–protognathodid fauna indicate higher energy conditions and a lowering of sea level associated with the boundary interval. In the eastern Arbuckle Mountains the D/C boundary is apparently conformable, marked by a green shale interval containing a Protognathodus fauna. Species of Siphonodella, indicative of an offshore setting, characterize the third and youngest fauna. The Early Carboniferous sulcata, Lower duplicata, and Upper duplicata Zones are recognized in the upper Woodford. The Woodford Shale is conformably overlain by the “pre-Welden Shale’ and its equivalents, or unconformably overlain by the lower Caney Shale (Osagean?–Meramecian) in the northern outcrop regions and the Sycamore Formation (late Osagean?–Meramecian) in the southern Arbuckle Mountains.

Correlation of chemostratigraphy, total organic carbon, sequence stratigraphy, and bioturbation in the Woodford Shale of south-central Oklahoma

2018 ◽  
Vol 6 (1) ◽  
pp. SC43-SC54
Author(s):  
Sabrina M. Coleman ◽  
Douglas W. Jordan
Keyword(s):  
Organic Carbon ◽  
Total Organic Carbon ◽  
Sequence Stratigraphy ◽  
Algal Blooms ◽  
Bottom Water ◽  
Woodford Shale ◽  
X Ray ◽  
South Central ◽  
Technological Advances ◽  
Water Conditions

Technological advances in handheld X-ray fluorescence (HHXRF) have been instrumental in demonstrating the utility of chemostratigraphic data to create higher order sequence stratigraphic interpretations. This study seeks to identify the correlation between chemostratigraphy, total organic carbon, sequence stratigraphy, and bioturbation in the Woodford Shale of south-central Oklahoma using HHXRF and X-ray diffraction technologies. The use of multiproxy correlations allows for higher confidence identifying lateral changes in the Woodford Shale. Elemental data collected through HHXRF can be used as proxies to better understand the depositional environment of a formation. Titanium, Zr, K, and Al are all proxies for transgression and regression. Silica is associated with so many different elements that Si alone does not provide useful information; however, the ratio of Si/Al coupled with detrital proxies can give information on the presence of possible algal blooms, continentally derived sediment, or hiatal surfaces. Furthermore, relationships between other elements can give further understanding to bottom-water conditions at the time of deposition. This study examines the relationships between Mo, V, Ni, and P along with other elements and laboratory-collected data to further understand the bottom-water conditions during deposition of the organic-rich muds that make up the Woodford Shale in south-central Oklahoma. To some extent, it is then possible to correlate these higher-resolution understandings to open-hole well logs to increase our understanding, where the core is unavailable.

Chemostratigraphic, palynostratigraphic, and sequence stratigraphic analysis of the Woodford Shale, Wyche Farm Quarry, Pontotoc County, Oklahoma

2015 ◽  
Vol 3 (1) ◽  
pp. SH1-SH9 ◽  
Author(s):  
Bryan W. Turner ◽  
Carlos E. Molinares-Blanco ◽  
Roger M. Slatt
Keyword(s):  
Gamma Ray ◽  
Data Sets ◽  
Well Log ◽  
Woodford Shale ◽  
Sequence Stratigraphic ◽  
Base Level ◽  
Area Of Interest ◽  
Significant Area ◽  
Shale Reservoirs ◽  
Well Log Analysis

Understanding mudrocks and shale reservoirs has become a significant area of interest within industry and academia in recent years. Of particular interest is understanding the pervasive variability present within these units. This variability became apparent when conventional approaches, such as lithostratigraphic analysis and well log correlation, were coupled with recent developments in palynostratigraphy and chemostratigraphy. A single shallow Woodford Shale research core in the western Arkoma Basin from Pontotoc County, Oklahoma, was used to identify three scales of stratigraphic cyclicity. By comparing the relative abundances of continental sourced pollen and spores to marine-derived acritarchs over a stratigraphic interval, it was possible to extrapolate the overall trends in shoreline trajectory. Conventional well log analysis, such as gamma ray logs, provided a balanced understanding of the interplay between localized changes in sedimentation and regional shifts in the stratigraphic base level, in addition to providing a means to tie these analyses to extensive subsurface data sets. Chemostratigraphic correlations resolved subtle, but stratigraphically significant, shifts in localized patterns in sedimentation. Using these approaches, the Lower and Middle Woodford Shale can be divided into four chemostratigraphic parasequences within a transgressive systems tract defined by well log and core analysis. The Upper Woodford can be separated into an additional four chemostratigraphic parasequences within a highstand systems tract. Chemostratigraphic data also revealed the changing bottom water conditions present at the time of deposition, with a period of localized anoxic conditions recorded in the Lower and Upper Woodford in this part of the basin. These localized changes in sedimentation and environmental conditions can be nested into two longer term regional transgressions and regressions.

scholarly journals High-Frequency Variability of the Surface Ocean Properties Off Central Chile During the Upwelling Season

2021 ◽  
Vol 8 ◽  
Author(s):  
Catalina Aguirre ◽  
René Garreaud ◽  
Lucy Belmar ◽  
Laura Farías ◽  
Laura Ramajo ◽  
...  
Keyword(s):  
High Frequency ◽  
Coastal Upwelling ◽  
Quantitative Description ◽  
Mean Flow ◽  
Austral Spring ◽  
Subtropical Anticyclone ◽  
Near Surface ◽  
Central Chile ◽  
South Central ◽  
High Frequency Variability

The ocean off south-central Chile is subject to seasonal upwelling whose intensity is mainly controlled by the latitudinal migration of the southeast Pacific subtropical anticyclone. During austral spring and summer, the mean flow is equatorward favoring coastal upwelling, but periods of strong southerly winds are intermixed with periods of relaxed southerlies or weak northerly winds (downwelling favorable). This sub-seasonal, high-frequency variability of the coastal winds results in pronounced changes in oceanographic conditions and air-sea heat and gas exchanges, whose quantitative description has been limited by the lack of in-situ monitoring. In this study, high frequency fluctuations of meteorological, oceanographic and biogeochemical near surface variables were analyzed during two consecutive upwelling seasons (2016–17 and 2017–18) using observations from a coastal buoy located in the continental shelf off south-central Chile (36.4°S, 73°W), ∼10 km off the coast. The radiative-driven diel cycle is noticeable in meteorological variables but less pronounced for oceanographic and biogeochemical variables [ocean temperature, nitrate (NO3−), partial pressure of carbon dioxide (pCO2sea), pH, dissolved oxygen (DO)]. Fluorescence, as a proxy of chlorophyll-a, showed diel variations more controlled by biological processes. In the synoptic scale, 23 active upwelling events (strong southerlies, lasting between 2 and 15 days, 6 days in average) were identified, alternated with periods of relaxed southerlies of shorter duration (4.5 days in average). Upwelling events were related to the development of an atmospheric low-level coastal jet in response to an intense along-shore pressure gradient. Physical and biogeochemical surface seawater properties responded to upwelling favorable wind stress with approximately a 12-h lag. During upwelling events, SST, DO and pH decrease, while NO3−, pCO2sea, and air-sea fluxes increases. During the relaxed southerly wind periods, opposite tendencies were observed. The fluorescence response to wind variations is complex and diverse, but in many cases there was a reduction in the phytoplankton biomass during the upwelling events followed by higher values during wind relaxations. The sub-seasonal variability of the coastal ocean characterized here is important for biogeochemical and productivity studies.

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