Sedimentary and Diagenetic Controls on Petroleum System Characteristics of the Upper Cretaceous Eagle Ford Group, South Texas


Book Description

Early diagenetic carbonate cements can affect brittleness and total organic content in shale reservoirs. Predicting these effects could potentially improve recovery efficiency and field development costs, and decrease the environmental impact of developing the field. In this study, an X-ray fluorescence spectroscopic technique was used to test for correlations between primary depositional features, diagenetic carbonate cements, and organic content and fracture distributions in core samples from the Eagle Ford Group in McMullen County, Texas. Organic content varies significantly between diagenetic facies, with the least organic matter present in coarsely mineralized shales. This result is consistent with the hypothesis that diagenetic carbonate cementation that was early relative to compaction diluted primary organic matter. In contrast, total fracture length varies significantly between depositional facies, with the lowest total fracture length per length of core present in massive shales. Carbonate diagenesis therefore likely did not exert a significant control on the formation of the bedding-parallel fractures observed in this study; instead, laminated fabrics provided planes of weakness along which stress release fractures or hydrocarbon generation-induced fractures could develop. The suggested target reservoir facies for similar Eagle Ford wells is a finely to moderately mineralized laminated shale because of the likelihood of finding high organic content and horizontal fractures that would increase the effective rock volume in communication with primary hydraulically induced fractures. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/152863




U-Pb Geochronology of the Late Cretaceous Eagle Ford Shale, Texas


Book Description

The Eagle Ford Shale and equivalent Boquillas Formation (Late Cretaceous) contain abundant volcanic ash beds of varying thickness. These ash beds represent a unique facies that displays a range of sedimentary structures, bed continuity, and diagenetic alteration. They are prominent not only in West Texas outcrops, but also in the subsurface of South Texas where hydrocarbon production is actively occurring. The ash beds have the potential to be used for stratigraphic correlation for understanding early diagenesis and -- most importantly -- for obtaining high-resolution geochronology, which can then be used for defining depositional rates and chronostratigraphy. Study of the ash beds was conducted at outcrops along U.S. 90, west of Comstock, Texas, the subsurface in Atascosa and Karnes County, and at a construction site in South Austin. Bed thicknesses range from 0.1-33 cm and were collected throughout the entirety of the Eagle Ford succession. Mineral separation yielded abundant non-detrital zircons for U-Pb dating. Dating was conducted using LA-ICP-MS at The University of Texas at Austin, to attain a base level understanding of the age range for the Eagle Ford. High-resolution ages for the base and top of the Eagle Ford were obtained, in addition to radioisotopically defining the Cenomanian-Turonian boundary within the section. U-Pb ages for the Eagle Ford Shale range from Early Cenomanian to Late-Coniacian near Comstock, Mid-Cenomanian to the Turonian-Coniacian boundary in the subsurface, and Early Cenomanian to Late Turonian in Austin area. These findings contrast with many of the regional biostratigraphic studies across the Eagle Ford and indicate a more prolonged period of Eagle Ford deposition than previously observed.




Geologic Controls on Production


Book Description

SEPM Field Trip Guidebook 16 is perhaps best thought of as an exercise in applied stratigraphy and structural geology. The technical goal is to make inter-disciplinary links, to demonstrate how stratigraphic and structural features affect exploration and development activities for unconventional hydrocarbon reservoirs.The outcrops described in this guidebook should help to stimulate discussion on a series of interrelated topics such as: lithology, stratigraphic controls on hydrocarbons, horizontal drilling target, and geosteering challenges.










Depositional Dynamics of the Upper Eagle Ford (Upper Cretaceous)


Book Description

The mixed siliciclastic/carbonate late Cretaceous Eagle Ford Formation is commonly divided into the lower Eagle Ford and the upper Eagle Ford. The lower Eagle Ford is arguably the most obvious organic rich interval highlighted with wireline log data; however, the upper Eagle Ford may have just as much potential for hydrocarbon production success as the lower Eagle Ford has had. A better understanding of the upper Eagle Ford will allow a more thorough and educated assessment into its full potential as an unconventional reservoir, and allow its sweet spots for oil or gas to be found and exploited. This study is based on the description and interpretation of four cores of the upper Eagle Ford located within Karnes and Gonzales counties, Texas, thin sections, and key XRF data in an effort to better understand its sediment sources and depositional regime. Seven lithofacies were identified in the upper Eagle Ford are as follows: 1) Bioturbated Wackestone/Packstone; 2) Deformed Wackestone/Packstone; 3) Wavy Laminated Wackestone/Packstone; 4) Massive Mudstone/Wackestone; 5) Coarsely to Finely Laminated Wackestone/Packstone; 6) Massive packstone/grainstone; 7) Volcanic Ash. The highest Total Organic Carbon (TOC) percent relative to each core always occurred within the base of the upper Eagle Ford. In fact, the highest TOC percentage recorded was 4.5% within the base of the upper Eagle Ford in the most distally located core. Thorium to Uranium ratios of the upper Eagle Ford were on average less than 1 indicating that the upper Eagle Ford contains very little terrigenous sourced material. Nickel, copper, vanadium, molybdenum, and uranium concentrations were also analyzed and correlated to relative organic matter influx and Paleoredox levels within the upper Eagle Ford in each core.




Shale


Book Description

Advances in theories, methods and applications for shale resource use Shale is the dominant rock in the sedimentary record. It is also the subject of increased interest because of the growing contribution of shale oil and gas to energy supplies, as well as the potential use of shale formations for carbon dioxide sequestration and nuclear waste storage. Shale: Subsurface Science and Engineering brings together geoscience and engineering to present the latest models, methods and applications for understanding and exploiting shale formations. Volume highlights include: Review of current knowledge on shale geology Latest shale engineering methods such as horizontal drilling Reservoir management practices for optimized oil and gas field development Examples of economically and environmentally viable methods of hydrocarbon extraction from shale Discussion of issues relating to hydraulic fracking, carbon sequestration, and nuclear waste storage Book Review: I. D. Sasowsky, University of Akron, Ohio, September 2020 issue of CHOICE, CHOICE connect, A publication of the Association of College and Research Libraries, A division of the American Library Association, Connecticut, USA Shale has a long history of use as construction fill and a ceramic precursor. In recent years, its potential as a petroleum reservoir has generated renewed interest and intense scientific investigation. Such work has been significantly aided by the development of instrumentation capable of examining and imaging these very fine-grained materials. This timely multliauthor volume brings together 15 studies covering many facets of the related science. The book is presented in two sections: an overview and a second section emphasizing unconventional oil and gas. Topics covered include shale chemistry, metals content, rock mechanics, borehole stability, modeling, and fluid flow, to name only a few. The introductory chapter (24 pages) is useful and extensively referenced. The lead chapter to the second half of the book, "Characterization of Unconventional Resource Shales," provides a notably detailed analysis supporting a comprehensive production workflow. The book is richly illustrated in full color, featuring high-quality images, graphs, and charts. The extensive index provides depth of access to the volume. This work will be of special interest to a diverse group of investigators moving forward with understanding this fascinating group of rocks. Summing Up: Recommended. Upper-division undergraduates through faculty and professionals.







Chemostratigraphy of the Upper Cretaceous from Central and South Texas with Focus on the Eagle Ford Group


Book Description

The fine-grained organic-rich rocks of the Eagle Ford (Cenomanian-Turonian) were deposited during the Upper Cretaceous in the shallow waters of the Western Interior Seaway. Five drill cores recovered from two counties, four from Travis County, Texas and one from Frio County, Texas, have been scanned from between two foot and half foot intervals with a hand-held energy-dispersive x-ray fluorescence (HH-ED-XRF) spectrometer to acquire major (e.g. Ca, Si, Al) and trace (e.g. Mo, V, Ni) element data for quantitative analysis. Additionally, gamma ray logs have been analyzed for two of the cores. Major element geochemistry indicates the Eagle Ford deposited in South Texas is different from the Eagle Ford deposited in Central Texas. South Texas Eagle Ford is much more Ca (carbonate) rich, with a noticeably lower Al (clay) content. South Texas and Central Texas Eagle Ford both have low Si (quartz) content relative to the Al and Ca content, indicating a negligible siliciclastic contribution during deposition. Trace element analysis reveals the redox conditions of the bottom waters during deposition. Mn -- an element which becomes mobile and may be removed from an open system in reducing conditions -- levels are much higher in the Austin Chalk and Buda with notably lower values in the Eagle Ford in both Central Texas and South Texas. Mo, an element which tends to bind with organic matter or sulfides during reducing conditions, is notably higher in the Eagle Ford of both South Texas and Central Texas. The correlation of decreased Mn levels and increased Mo levels suggests that the Eagle Ford was deposited in reducing conditions in an open system capable of removing mobilized Mn. Geochemical analysis of major and trace elements obtained from ED-XRF may be used in the petroleum industry in concert with XRD, electric logs, and standard core analysis to give a more complete picture of the depositional environment, clay type and volume, geophysical rock properties, and areal extent of a potential unconventional shale reservoir for hydrocarbon extraction. XRF data offers insight about the rocks, leading to improved understanding of the depositional environment and chemical makeup. Applying these technologies to the Eagle Ford helps unlock the potential of this significant hydrocarbon source and reservoir.