Article
Geosciences, Multidisciplinary
Autumn L. Eakin, Julia S. Reece, Kitty L. Milliken, Robert Locklair, Andrew P. Rathbun
Summary: Mineralogical composition plays a crucial role in the mechanical strength of tight mudrock reservoirs and is important for hydraulic fracturing. Through XRF and XRD analyses, the chemical composition and its impact on mechanical properties of mudrock from the Permian Wolfcamp formation and Spraberry Formation in Texas were studied. A novel workflow was developed to classify mudrocks based on chemofacies and predict cement-prone facies, which can aid in predicting mechanical properties and brittle fractures in unconventional reservoirs.
Article
Geosciences, Multidisciplinary
Stacy C. Atchley, Brian T. Crass, Kieron C. Prince
Summary: The Permian Basin in the southwestern United States has historically produced a significant amount of oil, but recent success in unconventional shale reservoirs has increased its potential for oil recovery. The Cline shale, a key reservoir in the area, has high oil-in-place estimates and plays a crucial role in influencing reservoir quality.
Article
Geosciences, Multidisciplinary
Zhaodong Xi, Shuheng Tang, Gary G. Lash, Yapei Ye, Donglin Lin, Bing Zhang
Summary: This paper focuses on the diagenetic history, pore structure, and brittleness of the Ordovician-Silurian Wufeng Formation and Longmaxi Formation in South China, and considers the possible impacts of mineralogy and organic matter contents and assemblages. The study reveals that the Wufeng Formation is enriched in organic matter and authegenic quartz, which are the dominant types of porosity. The precipitation of authegenic quartz reduces the porosity and increases the brittleness of the shale. In contrast, the depositional porosity of the Longmaxi Formation is largely reduced due to physical compaction. The extensive authegenic quartz cementation and thermal maturation of organic matter in the Wufeng Formation enhance its reservoir capacity and fracturing ability compared to the overlying Longmaxi Formation.
JOURNAL OF ASIAN EARTH SCIENCES
(2022)
Article
Geosciences, Multidisciplinary
L. Taras Bryndzia, Ruarri J. Day-Stirrat, Amie M. Hows, Jean-Philippe Nicot, Anton Nikitin, Ozkan Huvaz
Summary: This study reveals that the produced waters in the Permian Delaware Basin are primarily in situ Wolfcamp shale formation water, influenced by evaporative brines. The osmosis-diffusion model predicts high osmotic pressures in the Wolfcamp shale, resulting in significant water and oil production.
Article
Geosciences, Multidisciplinary
B. S. Hart, J. Schieber, J. Kalinec
Summary: We studied the origins of overpressure in Tertiary and Upper Cretaceous shales and sandstones in the northwestern Onshore Gulf of Mexico using cuttings and wireline logs. Our results suggest that clay diagenesis is the major source of excess pore pressure, rather than organic maturation. SEM imaging revealed nanoscale to microscale textural and mineralogic changes related to diagenesis. The experiment with cuttings demonstrated their utility and limitations. Additionally, our results challenge some assumptions about shale diagenesis used in pore-pressure studies.
MARINE AND PETROLEUM GEOLOGY
(2023)
Article
Geology
Junwen Peng
Summary: This study investigates the deep-water fine-grained sedimentary rocks in the Upper Pennsylvanian Cline Shale, Midland Basin, USA, through sedimentological, petrographic and bulk geochemical analysis of three cored wells. The findings reveal a repeated pattern of lithofacies stacking to form composite cycle sets, controlled by high-amplitude glacioeustatic sea-level fluctuation. The presence of sediment density flow deposits challenges the conventional model of deep-water sedimentation as dominantly background sedimentation.
Article
Geosciences, Multidisciplinary
Tongwei Zhang, Qilong Fu, Xun Sun, Paul C. Hackley, Lucy Tingwei Ko, Deyong Shao
Summary: Analysis of meter-scale lithofacies cycles in the Wolfcamp A formation showed that both TOC-rich mudstones and TOC-lean carbonate beds have high oil saturation index (OSI), indicating the presence of migrated oil. Residual gas analysis revealed lower dryness values and higher oil indicator values in TOC-lean carbonate beds compared to TOC-rich mudstones, suggesting a cumulative oil and gas charging effect through source rock maturation. Oil and gas generated at different thermal maturity stages were expelled into adjacent carbonate beds from OM-rich siliceous/calcareous mudstones, which plays a key role in variations of oil saturation in the Wolfcamp A.
Article
Geology
Kenneth Chukwuma, Harilaos Tsikos, Nicola Wagner
Summary: Diagenesis plays a crucial role in the evolution of mineralogical systems in shales, affecting the development of rock properties for unconventional reservoir prospectivity. A study of the Whitehill Formation in South Africa revealed systematic variations in early diagenetic reactions and products, influenced by the primary grain assemblages in different intervals. This research improves the characterization of shale mineralogical systems and properties for sustainable unconventional exploration.
SEDIMENTARY GEOLOGY
(2021)
Article
Geosciences, Multidisciplinary
Junwen Peng, Toti E. Larson
Summary: A novel integrated approach for chemofacies characterization of organic-rich mudrocks was developed using principal components analysis and clustering, which identified three chemofacies and their implications for shale oil production.
Article
Paleontology
Andrej Ernst, Anna Lene Claussen, Barbara Seuss, Patrick N. Wyse Jackson
Summary: An exceptionally well-preserved bryozoan fauna from the Finis Shale Member in Texas, USA is described. Nineteen bryozoan species were identified, including two new species. The growth forms of bryozoans varied in different locations along the profiles, with erect forms dominating. The profiles indicate a gradual shallowing, and bryozoan richness and diversity increase towards the top. The paleobiogeographic relations of the bryozoans are primarily restricted to the American realm, with some connections to Pennsylvanian of Europe.
PALAEONTOLOGIA ELECTRONICA
(2022)