Fusselman/Devonian Study. of the Midland Basin, Texas

Fusselman/Devonian Study of the Midland Basin, Texas

Fusselman-Devonian Study of the Midland Basin, Texas Overview The Fusselman-Devonian study of the Midland Basin is designed to enhance both exploration and development efforts that are directed at the prolific hydrocarbon reserves in the Fusselman and overlying Siluro- Devonian reservoirs. Most of the early exploration and development for these reservoirs occurred along the Fusselman truncation edge and on large seismically defined structures in the deeper portions of the Midland Basin. Recent activity has concentrated on smaller scale structural anomalies downdip from the Fusselman pinchout using 3-D seismic. All these "structural" reservoirs show a strong stratigraphic control on reservoir development and distribution. GDI has created an extensive correlation framework that documents detailed depositional and unconformity-related thickness variations in ten stratigraphic intervals. The mapping of these intervals is essential in the exploration for Fusselman/Devonian-age reservoirs. The Fusselman/Devonian study represents several man-years of geologic research which affords explorationists significant time savings in assimilating data and developing exploration strategies. The study area covers a six-county area including Dawson, Borden, Martin, Howard, Midland, and Glasscock counties in Texas. Correlations of 1,317 wells were made by defining 11 regional markers from the Silurian and Devonian of the Midland Basin. This geodigital framework provides clients with a valuable resource for interpreting the complex factors affecting reservoir quality. Descriptions of more than 3200 feet of section from 52 cores, petrographic examination of more than 300 thinsections, and log analyses of over 200 wells were incorporated in this regional synthesis. Fusselman/Devonian depositional models and lithofacies reservoir potential are determined through the integration of core, thinsection, log analyses, and engineering data. Six representative field studies are incorporated with a focus on Fusselman reservoir characteristics, trap types, and deliverability. The study components include an extensive summary text and figures, maps and cross sections, a volume containing core and thinsection descriptions integrated with core-to-log comparisons, and stratigraphic data appendices. Also included as part of the study is an executive summary and interpretive atlas. These components provide the client with a presentation format that is concise and readily useable. Database 1317 Study Wells 11 Regional Stratigraphic Markers Correlated 52 Cores Described 300 Thinsections

Maps Regional Maps (1:250,000) 9 Isopach Maps 2 Structure Maps 1 Woodford Subcrop Map Borden-Howard County Maps (1 : 96,000) 4 Isopach Maps 1 Structure Map 1 Study Well Index Map 1 Penetration Map of Study Wells 1 Production/Field Index Map 10 Regional Stratigraphic Sections Cross Sections 3 Log-Derived Calculated Lithology Section Field Studies Southeast Luther, Breedlove, RK, Moore, Mid-Mar, and Branum Fields Report Contents TEXT AND FIGURES - An extensively illustrated report includes discussions, figures, and color plates on: Executive Summary, Depositional Setting, Lithofacies, Stratigraphy, Depositional History, Petrography, Field Studies, Synthesis, and Exploration Potential. CORE DESCRIPTIONS - This report contains descriptions of 3200 feet of section from 52 cores. INTERPRETIVE ATLAS - This section contains all significant maps and cross sections, along with depositional and explorative models. STRATIGRAPHIC DATA - This section contains the stratigraphic data (11 formation tops, stratigraphic markers, and net sandstone values) and isopach values, as well as information on well name, operator, location, API number, completion date, datum, and production status for the 1317 study wells. MAPS AND CROSS SECTIONS - This appendix contains fourteen regional maps at a scale of 1 : 250,000 and 6 county maps at a scale of 1 : 96,000. This includes isopach maps, structure maps, subcrop map, and study well maps.

Fusselman/Devonian Study of the Midland Basin T 24 N R 18 W R 10 W T 24 N Lamesa DAWSON BORDEN MARTIN HOWARD Big Spring Stanton Midland Odessa MIDLAND GLASSCOCK 0 N MILES 10 T 14 N R 19 W Study Boundary R 11 W T 14 N

Fusselman/Devonian Study of the Midland Basin Study Table of Contents

TABLE OF CONTENTS Preface... i Acknowledgements... ii Table of Contents... iv List of Maps and Cross Sections... viii Summary Approach... S-2 Depositional Setting... S-3 Stratigraphy... S-4 Lithofacies and Diagenesis... S-4 Field Studies... S-4 Exploration Recommendations... S-5 Chapter 1 Introduction General Stratigraphy... 1-4 Chapter 2 Depositional Setting Tectonic Setting of the Tobosa Basin... 2-3 Siluro-Devonian sea-level fluctuations... 2-3 Pre-Woodford Tectonic Setting... 2-5 Siluro-Devonian Deposition... 2-5 Post-Woodford Tectonics... 2-6 Tectonic Model for Deposition... 2-7 Chapter 3 Stratigraphy Stratigraphic Picks... 3-2 Woodford Shale... 3-3 Woodford Marker... 3-3 Pre-Woodford Unconformity... 3-3 Thirtyone Formation... 3-4 Wristen Formation... 3-4 Upper Wristen... 3-4 Lower Wristen... 3-5 Lower Wristen Marker... 3-5 Fusselman Formation... 3-5 iv

Upper Fusselman... 3-5 Lower Fusselman... 3-6 Sylvan Shale... 3-6 Montoya Group... 3-7 Simpson Group... 3-7 Ellenburger Group... 3-7 Chapter 4 Lithofacies Green Shale Lithofacies 4-3 Oolitic Grainstone Lithofacies (Lower Fusselman)... 4-4 Peloidal Packstone to Grainstone Lithofacies... 4-5 Pisolitic Wackestone to Grainstone Lithofacies... 4-6 Massive to Laminated Dolomite Mudstone Lithofacies... 4-7 Echinoderm Grainstone to Packstone Lithofacies... 4-8 Boundstone Lithofacies... 4-9 Skeletal Wackestone Lithofacies... 4-10 Nodular Skeletal-Pelletal Wackestone Lithofacies... 4-11 Nodular to Brecciated Dolomite Lithofacies... 4-12 Bedded Chert Lithofacies... 4-13 Breccia Lithofacies... 4-13 Black Shale Lithofacies... 4-14 Chapter 5 Depositional History Ordovician History of the Tobosa Basin... 5-2 Ellenburger Deposition... 5-3 Simpson Deposition... 5-4 Montoya DePosition... 5-4 Sylvan Shale Deposition... 5-4 Silurian History of the TobosaBasin... 5-5 Fusselman Deposition... 5-6 Characteristics of the Lower Fusselman.. 5-6 Characteristics of the Upper Fusselman... 5-8 Wristen Deposition... 5-9 Characteristics of the Lower Wristen... 5-10 Characteristics of the Upper Wristen... 5-11 Devonian History of the Tobosa Basin... 5-12 Thirtyone Deposition... 5-12 Pre-Woodford Unconformity... 5-12 Woodford Shale... 5-13 v

Chapter 6 Petrography Types of Porosity... 6-2 Intergranular Porosity... 6-3 Vuggy Porosity in Limestones... 6-3 Intercrystalline Porosity... 6-5 Dolomitic Vuggy Porosity... 6-5 Breccia and Fracture Porosity... 6-6 Diagenetic Fabrics and Cement Types... 6-7 Marine Phreatic Cements... 6-8 Freshwater Phreatic Cements... 6-8 Freshwater Vadose Cements... 6-9 Burial Diagenesis and Cementation... 6-10 Types of Dolomite... 6-11 Penecontemporaneous Peritidal Dolomite... 6-11 Stylolite-Related Dolomite... 6-12 Other Burial Dolomites... 6-12 Diagenetic Model for the Fusselman... 6-14 Depositional and Diagenic History, Midland County... 6-16 Conclusions... 6-16 Chapter 7 Field Studies General Play Types... 7-3 Fields Selected for Detailed Analysis... 7-4 Fusselman/Wristen Pinchout Trend... 7-4 Southeast Luther Field... 7-4 Structural Traps with Dolomite Reservoirs... 7-6 Breedlove Field... 7-6 RK Field... 7-8 Moore Deep Field... 7-9 Mid-Mar Field... 7-10 Limestone Reservoir Field... 7-11 Branum Field... 7-11 Application of Field Studies... 7-12 Chapter 8 Exploration Recommendations Production and Reservoir Facies, Lower Fusselman... 8-3 Lower Fusselman Exploration Trends... 8-4 Production and Reservoir Facies, Upper Fusselman... 8-5 Upper Fusselman Exploration Trends 8-6 Production and Reservoir Facies, WristenFormation... 8-7 Wristen Formation Exploration Trends... 8-8 Production and Reservoir Facies, Thirtyone Formation.. 8-9 vi

Thirtyone Formation Exploration Trends... 8-10 BIBLIOGRAPHY Bibliography... B.1 The GDI Fusselman/Devonian report contains several separate components. components are listed below: These Text and Figures (This document) Executive Summary and Interpretive Atlas Core and Thin Section Descriptions Maps and Cross Sections Stratigraphic Database vii

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Fusselman/Devonian Study of the Midland Basin Selected Figures from the Study

Figure 1.1. West Texas structural elements. GDI study area lies within the central portion of the Midland Basin. This basin and the other major features shown formed as a result of late Paleozoic tectonics. As such, they did not influence Siluro-Devonian patterns. Return to Text

Figure 4.1. Generalized Fusselman lithofacies models. A) Distribution of lithofacies is related to a tectonically influenced paleobathymetry. Finer grained carbonates are associated with deeper water environments and protected lagoonal settings. B) Detailed facies tract of higher energy shoal-water facies. Radial ooids formed in high-energy settings were flanked by irregularly coated grains deposited in lower energy environments. Pisolites formed in soils on exposed surfaces. Return to Text

A Figure 7.19A. Rock types in the Mid-Mar Field reservoir - Epley #7, 11,736.5 ft. This sample from the reservoir in Mid-Mar Field shows the typical dirty (inclusion-rich) dolomite that replaced the limestones of the Fusselman during the formation of porosity in the field. This rock was originally the basal oolitic grainstone of the lower Fusselman, but only ghosts of the grains remain visible. Vuggy and intercrystalline porosity in the dolomite forms the reservoir in the field. Coarse clean crystals of dolomite fill some of the vuggy porosity. B Figure 7.19B. Rock types in the Mid-Mar Field reservoir - Oldham #2, 11,718 ft. Vuggy porosity and stylolites in the replacement dolomite which forms the reservoir interval in this well. Pervasive dolomitization has destroyed virtually all textures in the host limestone. Fractures associated with the stylolite appear to enhance porosity slightly. Continued on Next Page

Figure 6.18. Diagenetic history of the Simms #2 well, central Midland County. See Table 6.1 for explanation of major events. Return to Text Page 6-15 Return to Text Page 6-16

Example of a Core Description