Siluro-Devonian Study

Transcription

1 Siluro-Devonian Study of the Northern Tobosa Basin Texas & New Mexico

2 Siluro-Devonian of the Northern Tobosa Basin Overview This regional stratigraphic study of the Silurian and Devonian strata in the northern Permian Basin focuses on the exploration and production potential of Wristen and Fusselman carbonate reservoirs that were deposited in the Tobosa Basin. This study represents approximately eight man-years of geological research. All or portions of 12 counties and approximately 13,000 square miles in western Texas and southeastern New Mexico are included in the study area. The database includes 3,169 wells with 11 regional markers and up to eight additional subregional markers or internal markers correlated. Ten regional cross sections were constructed across the study area, with formation-level contacts from the Ellenburger through the Woodford correlated. Mapping of internal picks within Siluro-Devonian carbonates permitted the interpretation of the development of this complex platform-dominated system. The scientific team described 88 cores comprising more than 8,500 total feet. The cores were systematically sampled for petrographic analyses where permitted. Analyses of 550 thinsections are integrated into the core descriptions. The described cores comprise a complex suite of lithofacies deposited in diverse depositional environments, ranging from distal lower ramp to restricted supratidal. Stromatoporoid and coralline buildups are pervasive. The presence of repeated shoaling-upwards cycles terminating at subaerial exposure surfaces indicates the presence of multiple regional to subregional disconformities. Original depositional textures are often obscured by intense dolomitization and/or brecciation associated with the development of karst profiles. The seven field studies contain development geology and engineering analyses including detailed geologic mapping and modeling, evaluations of drive mechanisms, reservoir characterization, reserve evaluations, and well performance reviews. Selected seismic lines provided by Permian Exploration Corp. illustrate structural styles and trap types of several of the fields. Database 3,169 Study Wells 11 Regional Stratigraphic Markers Correlated 8 Internal Markers Correlated 88 Cores Described 550 Thinsections Maps 19 Regional and Field Maps (structure, isopach, and facies maps)

3 Cross Sections 10 Regional Stratigraphic Sections (vertical scale 1 inch = 100 feet) 12 Field Stratigraphic sections (vertical scale 1 inch = 40 feet) Field Studies New Mexico Peterson, Roosevelt County Langley Deep Field, Lea County Texas Mound Lake Field, Terry County, Dollarhide Field, Andrews County Hutex Field, Andrews County, Brahaney Field, Yoakum County, Walker Field, Cochran County Report Contents TEXT AND FIGURES - This report includes discussions of the following topics: Regional Tectonic and Environmental Setting, Depositional History and Models, Lithofacies, Petrography and Diagenetic History, and Exploration Recommendations. Also included are detailed field studies. CORE DESCRIPTIONS - This report includes both graphic and detailed written descriptions of more than 8500 feet of section from 88 cores, core-to-log comparisons, and interpreted depositional environments. Analyses of 550 thinsections are integrated into these core descriptions. STRATIGRAPHIC DATA - These files contain: tops, net porosity, and interval thickness values for 3,169 study wells. A study well reference guide provides an index for locating well data. This data file includes header information and a total of 19 formation tops and stratigraphic markers for the study wells. MAPS AND CROSS SECTIONS - These components are used for regional correlation and mapping applications. This includes 19 maps at a scale of 1:190,000 showing the distribution of wells, structural elements, sedimentary and diagenetic facies, porosity, and production. This also includes 10 regional and detailed stratigraphic cross sections.

4 Siluro/Devonian of the Northern Tobosa Basin Clovis DE BACA Study Boundary ROOSEVELT PARMER CASTRO SWISHER BAILEY LAMB HALE CHAVEZ COCHRAN HOCKLEY LUBBOCK Lubbock Roswell LEA NEW MEXICO TEXAS YOAKUM GAINES TERRY LYNN Lamesa DAWSON EDDY Carlsbad ANDREWS MARTIN 0 N MILES 40 Midland

5 Siluro/Devonian of the Northern Tobosa Basin Study Table of Contents

6 SILURO-DEVONIAN OF THE NORTHERN TOBOSA BASIN TABLE OF CONTENTS Preface Table of Contents...i List of Figures. ix List of Maps and Cross Sections.... xxviii Authors and Contributors..xxx Acknowledgements... xxxi Executive Summary Executive Summary Scope of the Study...S-1 Depositional Setting... S-1 Stratigraphy...S-2 Lithofacies... S-3 Petrography: Porosity and Diagenesis...S-5 Subaerial Exposure...S-6 Depositional History... S-7 Exploration Recommendations... S-9 Field Studies... S-12 Chapter 1 Introduction Goals and Objectives Study Area Scope of Study Stratigraphic Database Cores Petrographic Database Chapter 2 Depositional Setting Introduction Plate Tectonics and Basin Development Paleolatitude and Climate. 2-4 i

7 Chapter 3 Stratigraphy Introduction Ellenburger Group Contacts Thickness and Distribution Simpson Group Contacts Thickness and Distribution Montoya Group Contacts Thickness and Distribution Sylvan Shale Contacts Thickness and Distribution Siluro-Devonian Carbonates Fusselman Formation Contacts Thickness and Distribution F900-Sylvan (SLVN) Interval F500-F900 Interval Fusselman-F500 Interval Fusselman Formation Summary Wristen Formation Contacts Thickness and Distribution W700-FSLM Interval W600-W700 Interval W500-W600 Interval W400-W500 Interval W300-W400 Interval WRSTN-W300 Interval Wristen Formation Summary Thirtyone Formation Contacts Thickness and Distribution T500-WRSTN Interval THON-T500 Interval Thirtyone Formation Summary Summary of Siluro-Devonian Carbonates Pre -Woodford Unconformity Woodford Shale Contacts Thickness and Distribution Woodford Intervals Stratigraphic Summary ii

8 Chapter 4 Lithofacies Introduction General Carbonate Facies Belts Facies Belt 1: Basin Facies Belt 2: Open Shelf Facies Belt 3: Deep Shelf Margin Facies Belt 4: Foreslope/Forereef Facies Belt 5: Reefs/Buildups Facies Belt 6: Winnowed Sands Facies Belt 7: Lagoon/Restricted Circulation Platform Facies Belt 8: Peritidal/Restricted Circulation Platform Facies Belt 9: Supratidal General Siliciclastic Lithofacies Black Laminated Shale Fine-Grained Sandstone Glauconitic and Dolomitic Sandstone and Sandy Dolomite Green Shale Shaly Sandstone/Siltstone Tripolitic Chert Lithofacies Tripolitic Chert Breccia Planar-Bedded Tripolitic Chert Chapter 5 Petrography: Porosity and Diagenesis Introduction Methods Porosity Types Interparticle Porosity Fusselman Formation Wristen Formation Thirtyone Formation Interparticle/Moldic Porosity Fusselman Formation Wristen Formation Thirtyone Formation Vuggy Porosity Fusselman Formation Wristen Formation Other Porosity Types Intercrystalline Porosity Fracture and Breccia Porosity Channel Porosity Diagenesis Introduction Early Shallow Marine Diagenesis Meteoric Diagenesis Dolomitization iii

9 Fusselman Formation Wristen Formation Thirtyone Formation Burial Diagenesis Silicification Dedolomitization Dolomite Dissolution Conclusions Chapter 6 Subaerial Exposure: Effects on Diagenesis and Porosity Development Introduction Depositional and Diagenetic Features Associated with Subaerial Exposure Stratigraphic and Geomorphic Features Macroscopic Features Molds and Vugs Solution Enlargement of Fractures and Joints Caves and Caverns In Situ Breccias Solution-Collapse Breccias Channel Pores Boxwork Textures Internal Sediment Microscopic Features Infiltrated Sediment Vadose Cements Altered Grains Freshwater Enlargement of Pores and Etching of Cements Conclusions Chapter 7 Depositional History and Models Introduction Ordovician Basin Evolution Ellenburger Group Simpson Group Montoya Group Sylvan Shale Silurian Basin Evolution Fusselman Formation Lower Fusselman (F900-SLVN Interval) Middle Fusselman (F500-F900 Interval) Upper Fusselman (FSLM-F500 Interval) Wristen Formation Lower Wristen (W700-FSLM Interval) iv

10 Middle Wristen (W600-W700, W500-W600, and W400-W500 Intervals) Wristen Reef Characteristics Upper Wristen (W300-W400 and WRSTN-W300 Int) 7-13 Devonian Basin Evolution Thirtyone Formation Eastern Andrews County Western Andrews County Lower Thirtyone (T500-WRSTN) Upper Thirtyone (THON-T500) Middle to Late Devonian Erosion Woodford Shale Summary Platform/Ramp Evolution Transgressive-Regressive Sequences Tectonics Chapter 8 Exploration Recommendations Introduction Montoya Group Review Exploration Strategy Lower Fusselman (F900-SYLVN) Review Paleotectonics Exploration Strategy Upper Fusselman (FSLM-F900) Review Paleotectonics Exploration Strategy Lower Wristen(W700-FSLM) Review Paleotectonics Exploration Strategy Middle Wristen(W400-W700) Review Paleotectonics Exploration Strategy Upper Wristen(WRSTN-W400) Review Paleotectonics Exploration Strategy Thirtyone Formation Review Exploration Strategy History of Siluro-Devonian Fields v

11 Chapter 9 Field Studies Preface. 9-1 General Introduction Approach to Reservoir Engineering Brahaney Field Introduction... 9-BF-1 Database...9-BF-1 Structure...9-BF-2 Present Structure...9-BF-2 Paleostructure... 9-BF-3 Stratigraphy...9-BF-3 Lithofacies and Karst Processes...9-BF-4 Oil Generation, Migration, and Entrapment...9-BF-5 Reservoir Characteristics... 9-BF-5 Petrology... 9-BF-5 Porosity and Permeability...9-BF-6 Porosity Transforms...9-BF-6 Relationship of Porosity and Permeability to Facies...9-BF-7 Geometry...9-BF-9 Petrophysical Properties...9-BF-9 W600-W700 Interval...9-BF-9 W700-FSLM Interval...9-BF-10 Reservoir Fluids... 9-BF-10 Reservoir Performance... 9-BF-11 Summary...9-BF-14 Hutex Field Introduction... 9-HF-1 Database...9-HF-2 Structure...9-HF-2 Present Structure... 9-HF-2 Paleostructure... 9-HF-3 Stratigraphy... 9-HF-3 Fusselman Formation...9-HF-3 Wristen Formation... 9-HF-3 Woodford Shale...9-HF-4 Lithofacies... 9-HF-5 Types...9-HF-5 Relationships... 9-HF-6 Reservoir Characteristics... 9-HF-6 Geometry...9-HF-7 Porosity and Permeability...9-HF-7 Reservoir Fluids... 9-HF-9 Reservoir Performance... 9-HF-10 Summary...9-HF-13 vi

12 Mound Lake Field Introduction... 9-MLF-1 Database...9-MLF-2 Stratigraphy...9-MLF-2 Lithofacies and Depositional Environment... 9-MLF-3 Structure...9-MLF-4 Present Structure...9-MLF-4 Paleostructure... 9-MLF-4 Petrophysics...9-MLF-6 Logging Suite...9-MLF-6 Facies Identification...9-MLF-6 Special Studies...9-MLF-7 Oil Generation, Migration, and Entrapment...9-MLF-7 Reservoir Characteristics... 9-MLF-8 Petrology... 9-MLF-8 Porosity and Permeability...9-MLF-8 Reservoir Fluids... 9-MLF-9 Reservoir Performance... 9-MLF-9 Field Economics...9-MLF-11 Summary...9-MLF-11 Walker Field Introduction... 9-WF-1 Database...9-WF-1 Structure...9-WF-2 Present Structure...9-WF-2 Paleostructure... 9-WF-2 Stratigraphy...9-WF-3 Lithofacies and Depositional Environment... 9-WF-3 Fusselman Formation...9-WF-3 Wristen Formation... 9-WF-4 Woodford Shale...9-WF-4 Petrophysics...9-WF-5 Facies Identification...9-WF-5 Special Studies...9-WF-6 Reservoir Characterization...9-WF-6 Porosity and Permeability...9-WF-6 Reservoir Performance...9-WF-7 Field Economics...9-WF-8 Summary...9-WF-8 Peterson South Field Introduction... 9-PSF-1 Database...9-PSF-1 Structure...9-PSF-2 Present Structure...9-PSF2- Paleostructure... 9-PSF-2 Stratigraphy...9-PSF-2 Lithofacies and Depositional Environment... 9-PSF-3 Petrophysics...9-PSF-4 Special Studies...9-PSF-4 vii

13 Reservoir Characterization...9-PSF-5 Porosity and Permeability...9-PSF-5 Reservoir Performance...9-PSF-6 Field Economics...9-PSF-7 Summary... 9-PSF-8 Langley Deep Field Introduction... 9-LDF-1 Discovery and Field Data... 9-LDF-1 Method of Study LDF-2 Geologic Setting and Structure... 9-LDF-2 Stratigraphy and Lithofacies Distribution...9-LDF-2 Wristen W300-W400 Interval...9-LDF-3 Wristen WRSTN-W300 Interval...9-LDF-4 Petrophysics...9-LDF-6 Reservoir Characteristics... 9-LDF-8 Porosity and Permeability...9-LDF-8 Reservoir Performance... 9-LDF-9 Field Economics...9-LDF-11 Summary...9-LDF-12 Dollarhide Field Introduction... 9-DHF-1 Discovery and Development... 9-DHF-1 Reservoir Lithology... 9-DHF-2 Tripolitic Chert Breccia... 9-DHF-2 Planar-Bedded Porous Tripolitic Chert...9-DHF-3 Nonporous Crinoid-Rich Packstone and Grainstone.. 9-DHF-4 Variably Porous and Siliceous Dolomite Packstone and Grainstone... 9-DHF-5 Dense Chert Breccia and Glauconitic Sandstone... 9-DHF-5 Play Concepts... 9-DHF-6 Conclusions Conclusions...9-CON-1 Bibliography Bibliography... B-1 viii

14 LIST OF FIGURES EXECUTIVE SUMMARY Figure S.1. Figure S.2. Figure S.3. Figure S.4. Figure S.5. Figure S.6. Figure S.7. Figure S.8. Figure S.9. Figure S.10. Figure S.11. Location map showing "Siluro-Devonian of the Northern Tobosa Basin" study area. The paleogeographic setting of the study area during Siluro-Devonian time. Tectonic elements of the Permian Basin area. Picks and markers used for the stratigraphic database for this study. Subcrop map for the Woodford Shale through the study area. Stratigraphic relationships of Siluro-Devonian strata in the Northern Tobosa Basin. Classification of the depositional facies of Siluro-Devonian carbonates of the study area. Reef and Reef-associated facies are common within the rocks of the Wristen Formation. A comparison of the hinge lines as defined by isopachs of the middle (F500- F900) and upper Fusselman (FSLM-F500). Wristen depositional patterns as reflected in the position of the hinge line during progressive stages of deposition. Location of fields studied in GDI's "Siluro-Devonian of the Northern Tobosa Basin." CHAPTER 1: INTRODUCTION Figure 1.1. Figure 1.2. Figure 1.3. Figure 1.4. Figure 1.5. Graph showing the relationship of the cumulative amount of oil discovered in Siluro-Devonian reservoirs in the Texas portion of the study area as a function of the fields' discovery dates. Map of RPI study area relative to the major structural components of the Permian Basin. Index map of the GDI "Siluro-Devonian of the Northern Tobosa Basin" study area. Locations of wells included in the GDI database. Regional grid of cross sections. ix

15 Figure 1.6. Figure 1.7. Figure 1.8. Figure 1.9. Picks and markers used for the stratigraphic database for this study. Wells selected for lithology and porosity calculation. Distribution of Siluro-Devonian cores described in detail for this study. Representative example of the core description format employed in this study. CHAPTER 2: DEPOSITIONAL SETTING Figure 2.1. Figure 2.2. Figure 2.3. Figure 2.4. Figure 2.5. Index map showing the major physiographic provinces dominating the southern Mid-continent from Cambrian through Devonian time. Paleogeographic reconstruction of the Tobosa Basin and vicinity. Tectonic elements of the southern Mid-continent during the Late Pennsylvanian. Tectonic elements of the Permian Basin. Schematic diagram of the tectonic history of the Permian Basin. CHAPTER 3: STRATIGRAPHY Figure 3.1. Figure 3.2. Figure 3.3. Figure 3.4. Figure 3.5. Figure 3.6. Figure 3.7. Figure 3.8. Figure 3.9. Figure Figure Correlation chart of Ordovician, Silurian, and Devonian units in west Texas and southwestern Oklahoma. Study interval type log from southern Andrews County, Texas. Type log illustrating the log character of the Simpson (SMPS), Ellenburger (ELBG), and base of the Ordovician (BORD) markers. Isopach map of the Ellenburger Group. Ellenburger cross section. Isopach map of the Simpson Group. Cross section illustrating northward truncation of the Simpson Group by the pre- Montoya unconformity. Isopach map of the Montoya Group. Core photographs of selected stratigraphic contacts and intervals. Lithology map of the Sylvan Shale. Isopach map of the Sylvan Shale. x

16 Figure Isopach map of the Sylvan Shale in the Midland Basin area (RPI, 1987). Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Isopach map of the Siluro-Devonian carbonate units (Fusselman, Wristen and Thirtyone formations). Cross section illustrating stratigraphic relationships of the Fusselman, Wristen, and Thirtyone formations. Isopach map of the Fusselman Formation. Core-to-log comparison of the lower Fusselman interval. Lithology map of the F900-SLVN interval of the Fusselman Formation. Isopach map of the F900-SLVN interval of the Fusselman Formation. Lithology map of the F500-F900 interval of the Fusselman Formation. Isopach map of the F500-SLVN interval of the Fusselman Formation. Lithology map of the FSLM-F500 interval of the Fusselman Formation. Isopach map of the FSLM-F500 interval of the Fusselman Formation. Interpretive cross section of Fusselman Formation stratigraphy. Cross section illustrating the unconformity between the Wristen and Thirtyone formations. Isopach map of the Wristen Formation. Lithology map of the W700-FSLM interval of the Wristen Formation. Isopach map of the W700-FSLM interval of the Wristen Formation. Lithology map of the W600-W700 interval of the Wristen Formation. Isopach map of the W600-W700 interval of the Wristen Formation. Lithology map of the W500-W600 interval of the Wristen Formation. Isopach map of the W500-W600 interval of the Wristen Formation. Lithology map of the W400-W500 interval of the Wristen Formation. Isopach map of the W400-W500 interval of the Wristen Formation. Lithology map of the W300-W400 interval of the Wristen Formation. Isopach map of the W300-W400 interval of the Wristen Formation. xi

17 Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Lithology map of the WRSTN-W300 interval of the Wristen Formation. Isopach map of the WRSTN-W300 interval of the Wristen Formation. Interpretive cross section of Wristen Formation stratigraphy. Isopach map of the Thirtyone Formation. Core photographs of selected textures in Thirtyone Formation. Lithology map of the T500-WRSTN interval of the Thirtyone Formation. Lithology maps of lower and upper portions of the THON-T500 interval of the Thirtyone Formation. Interpretive cross section illustrating stratigraphic relationships of the Fusselman, Wristen, and Thirtyone formations. Subcrop map of the pre-woodford unconformity. Cross section illustrating northward truncation of units by the pre-woodford unconformity. Isopach map of the Woodford Shale. Cross section illustrating stratigraphic relationships of the Woodford sandstone. Cross section illustrating stratigraphic relationships of the WDFDB marker. Isopach map of the WDFDB-UNCON interval of the Woodford Shale. Isopach map of the WDFD-WDFDB interval of the Woodford Shale. CHAPTER 4: LITHOFACIES Figure 4.1. Figure 4.2. Figure 4.3. Figure 4.4. Figure 4.5. Distribution of cores described for GDI's "Siluro-Devonian of the North Tobosa Basin" study. Siluro-Devonian facies belts and depositional environments are classified using an adaption of Wilson's (1975) standard carbonate facies model. Core photographs representative of the Basinal and Open Shelf facies belts. Core photographs representative of the Deep Shelf Margin and Foreslope/Forereef facies belts. Modifying terms for the different types of boundstones as recognized for Devonian rocks in Canada by Embry and Klovan (1971). xii

18 Figure 4.6. Figure 4.7. Figure 4.8. Figure 4.9. Figure Figure Figure Photos of various types of Wristen boundstones. Representative core photographs and photomicrographs of Fusselman oolitic grainstones deposited in the Winnowed Sands Facies Belt. Core photographs of skeletal and peloidal grainstones deposited in Facies Belts 6B and 6C. Photomicrographs of skeletal grainstones deposited in the Winnowed Sand Facies Belt (6B) and examples of carbonate rocks deposited in Lagoon/Restricted Circulation Platform facies belt (Facies Belt 7). Core photographs of several rock types representative of Peritidal/Restricted Circulation Platform Facies Belt. Core photographs of a selected sampling of the diverse rock types of the Supratidal Facies Belt. Core photographs of clastic lithologies occurring within Siluro-Devonian strata of the study area. CHAPTER 5: PETROGRAPHY: POROSITY AND DIAGENESIS Figure 5.1. Figure 5.2. Figure 5.3. Figure 5.4. Figure 5.5. Figure 5.6. Figure 5.7. Figure 5.8. Figure 5.9. Figure Figure Figure Map showing the location of thinsection samples providing the petrographic database for this study. Classification of porosity types and abbreviations used in this study (after Choquette and Pray, 1970). Representative photomicrographs of interparticle porosity. Representative photomicrographs of moldic and intraparticle porosity. Representative photomicrographs of moldic and intraparticle porosity (continued). Representative photomicrographs of vuggy porosity. Representative photomicrographs of intercrystalline porosity. Representative photomicrographs of fracture, breccia, and channel porosity. Representative photomicrographs illustrating early shallow marine diagensis. Schematic diagram illustrating the hydrologic model for the platform area during Siluro-Devonian time. Photomicrographs illustrating styles of dolomitization. Photomicrographs illustrating styles of burial diagenesis. xiii

19 Figure Photomicrographs illustrating the types of silica diagenesis observed in Siluro- Devonian samples. CHAPTER 6: SUBAERIAL EXPOSURE: EFFECTS ON DIAGENESIS AND POROSITY DEVELOPMENT Figure 6.1. Figure 6.2. Figure 6.3. Figure 6.4. Figure 6.5. Figure 6.6. Figure 6.7. Representative core photographs and photomicrographs of macroscopic indicators of karst. Representative core photographs of macroscopic indicators of short-term subaerial exposure. Representative core photographs of macroscopic indicators of long-term subaerial exposure and karsting. Representative core photographs of macroscopic indicators of long-term subaerial exposure/karst (continued). Representative core photographs of karst-related breccias (cave and in situ). Representative core photographs of karst-related solution collapse breccias. Representative photomicrographs of karst-related microscopic features. CHAPTER 7: DEPOSITIONAL HISTORY AND MODELS Figure 7.1. Figure 7.2. Figure 7.3. Figure 7.4. Figure 7.5. Figure 7.6. Figure 7.7. Figure 7.8. Figure 7.9. Figure Figure Paleobathymetric curve for southern Andrews County. Comparison of North American paleobathymetric curves. Sylvan Shale lithology and thickness trends. Paleogeographic reconstruction of Sylvan Shale. Distribution of lower Fusselman lithology and facies. Lower Fusselman thickness and porosity trends. Paleogeographic reconstruction of lower Fusselman deposition. Distribution of middle Fusselman lithology and facies. Middle Fusselman thickness and porosity trends. A) Paleogeographic reconstruction of middle Fusselman deposition. B) Facies trends on the evolving platform. Distribution of upper Fusselman lithology and facies. xiv

20 Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Upper Fusselman thickness and porosity trends. Paleogeographic reconstruction of upper Fusselman deposition. Distribution of lower Wristen lithology and facies. Lower Wristen thickness and porosity trends. Paleogeographic reconstruction of lower Wristen deposition. Thickness and facies variations due to differential subsidence. Middle Wristen lithologic distribution. Middle Wristen facies distribution. Middle Wristen thickness trends. Middle Wristen porosity trends. Middle Wristen paleogeographic reconstruction illustrating deposition on a well established platform. Idealized vertical sequence of a reef complex in the Wristen Formation in the Northern Tobosa Basin. Depositional Model for Wristen reefs. Faunal associations in Wristen reefs. Upper Wristen lithologic distribution. Upper Wristen facies distribution. Upper Wristen thickness trends. Upper Wristen porosity trends. Upper Wristen paleogeographic reconstruction. Depositional model illustrating the facies and faunal assemblage of a platform with restricted circulation. Woodford subcrop map. Lower Woodford isopach map. Upper Woodford isopach map. Fusselman hinge line trends. xv

21 Figure Wristen hinge line trends. CHAPTER 8: EXPLORATION RECOMMENDATIONS Figure 8.1. Figure 8.2. Figure 8.3. Figure 8.4. Figure 8.5. Figure 8.6. Figure 8.7. Figure 8.8. Figure 8.9. Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Composite strategy map for the Montoya Group. Montoya isopach map with interpreted block fault boundaries. Interval isopachs for Fusselman and Wristen formations within the zone of subcrop for each interval and block fault interpretation. WDFDB-UNCON isopach map with block fault interpretation. F900-SLVN Composite strategy map. UNCON-FSLM isopach map for portions of Yoakum, Cochran, Lea, and Roosevelt Counties. Fusselman Composite strategy map for the truncation zone. FSLM-F500 Composite Strategy map for the deep structural play. W700-FSLM composite porosity map. FSLM-F500 isopach map showing thins along platform margin area. W700-FSLM isopach map showing thicks along platform margin area. Composite strategy map for W700-FSLM interval. UNCON-W700 isopach map of Brahaney Field area. Detailed WDFDB-UNCON isopach map in Yoakum and northern Gaines Counties. W600-W700 Composite strategy map. W500-W6OO Composite strategy map. W400-W500 Composite strategy map. W600-W700 porosity overlay on W700-FSLM porosity. W300-W400 Composite strategy map. WRSTN-W300 Composite strategy map. WRSTN-W300 porosity with overlay of paleotectonic blocks. xvi

22 Figure Figure Figure Figure Histograms showing the frequency of field sizes in ultimate barrels of oil per field. Distribution of Siluro-Devonian oilfield sizes in a ranking from largest ultimate BO to smallest ultimate BO for 50 mature oilfields in Andrews County, Texas. Distribution of Siluro-Devonian oilfield sizes. Siluro-Devonian oilfield sizes in ultimate barrels of oil per field plotted versus the discovery date of the field. CHAPTER 9: FIELD STUDIES Figure 9.1. Location of the fields selected for detailed study. BRAHANEY FIELD Figure 9.BF-1. Figure 9.BF-2. Figure 9.BF-3. Figure 9.BF-4. Figure 9.BF-5. Figure 9.BF-6. Figure 9.BF-7. Figure 9.BF-8. Figure 9.BF-9. Figure 9.BF-10. Figure 9.BF-11. Location of Brahaney Field and its relation to major structural provinces in the Permian Basin. Index map of the Brahaney Field area showing the location, initial status, and API numbers of the Silurian wells. Chronologic development of Brahaney Field. Location of wells in the Brahaney Field area with non-silurian hydrocarbon shows and production. Structure map for the Brahaney Field area contoured on the top of the Woodford Shale. Isopach map of the W600-W700 interval in Brahaney Field. Type log showing the subdivision, wireline-log character, carbonate texture, and inferred depositional environment of the Siluro-Devonian section at Brahaney Field. Selected core photographs of the Wristen Formation from the Melba Webb "D" #1 well in Brahaney Field. Thinsection photomicrographs of the Wristen dolomites in Brahaney Field. Vertical zonation of exposure-related diagenetic features and karst overprinting, and its relation to primary texture, in core from the Getty Melba Webb "D" #1 well. Crossplot of sonic transit time and core-derived porosity for the Melba Webb "D" #1 well. xvii

23 Figure 9.BF-12. Figure 9.BF-13. Figure 9.BF-14. Figure 9.BF-15. Figure 9.BF-16. Figure 9.BF-17. Figure 9.BF-18. Figure 9.BF-19. Figure 9.BF-20. Figure 9.BF-21. Figure 9.BF-22. Figure 9.BF-23. Figure 9.BF-24. Figure 9.BF-25. Figure 9.BF-26. Figure 9.BF-27. Figure 9.BF-28. Figure 9.BF-29. Crossplot of neutron-density porosity and sonic porosity data for Brahaney Field. Ranges in permeability and porosity values for four classes of porosity in the Getty Melba Webb "D" #1 well in Brahaney Field. Crossplot of porosity and permeability determined from analysis of core plugs from Getty Melba Webb "D" #1 well. Histogram showing frequency of permeability plotted by petrographic porosity type in the Getty Melba Webb "D" #1. Distribution of core permeability for samples from the Getty Melba Webb "D" #1. Definition of "V," the Dykstra-Parsons coefficient of permeability variation, as shown by Craig (1971, p. 65). Cumulative k x h (flow capacity) and cumulative x h (porosity-ft) plotted against core porosity for the Getty Melba Webb "D" #1 reservoir. Wireline logs from the Getty J.H. Beshears "D" #1 well. Wireline logs from the Hunt Oil Hicks "A" #1 showing the effects of formation brecciation on log response. Bulk Volume Water (BVW) plot for the Getty J.H. Beshears "D" #2 well. Bulk Volume Water (BVW) plot for the Siluro-Devonian interval at the Hunt Oil Hicks "A" #1 well. Locations of wells plotted with ranking numbers showing the rate of water/oil ratio increase. Initial water cut (%), from operator-reported initial potential test results. Variation in the gross thickness of the oil column at Brahaney Field. Contour map of ultimate oil recovery from the Wristen reservoir in Brahaney Field. Contour map of ultimate oil recovery per foot of gross pay in Brahaney Field. Cross plot of ultimate oil recovery per porosity-foot of pay versus structural position of the Woodford Shale. Production decline curve for an average well in Brahaney Field. xviii

24 HUTEX FIELD Figure 9.HF-1. Figure 9.HF-2. Figure 9.HF-3. Figure 9.HF-4. Figure 9.HF-5. Figure 9.HF-6. Figure 9.HF-7. Figure 9.HF-8. Figure 9.HF-9. Figure 9.HF-10. Figure 9.HF-11. Figure 9.HF-12. Figure 9.HF-13. Figure 9.HF-14. Figure 9.HF-15. Figure 9.HF-16. Location of Hutex Field in relation to major structural provinces in the Permian Basin. Index map of the field study area showing the location and initial status of Silurian penetrations. Location of wells producing from non-silurian strata in the Brahaney Field area. Top Woodford subsea depths and structure map contoured on the top of the Woodford Shale. Type log selected for Hutex Field showing the stratigraphy, wireline-log character, and dominant lithology of the Silurian section in the field. Producing intervals in the Wristen Formation at Hutex Field. Core photographs of the Silurian rocks in Hutex Field. Core photographs and thinsection photomicrographs of Hutex Field reservoir rocks. Fence diagram showing lateral and vertical facies relationships and the relation of facies to production at Hutex and Magutex fields. Schematic facies model showing the facies that produce oil at Hutex and Magutex fields. Lateral trends in porosity and the relationship of porosity to lithology and facies in the upper 30 feet of the Wristen Formation. Relationship of porosity to lithology in the southern part of the Hutex Field. Crossplot of core porosity and permeability in the Humble State University "W" #1 well, a producer in Magutex Field. Distribution of core permeability for samples from the Humble State University "W" #1 well representing the peritidal facies of the W400-W500 interval. Histogram showing frequency of permeability values in core samples from the Humble State University "W" #1 well representing peritidal facies of the W400-W500 interval. Crossplot of core porosity and permeability determined from core plugs from the Humble State University wells "AX" #1, "S" #2, and "BQ" #2. Data represent the reef/reef flank apron facies of the W400-W500 interval. xix

25 Figure 9.HF-17. Permeability distribution of the reef/reef flank apron facies of the W400- W500 interval in the Humble State University wells "AX" #1, "S" #2, and "BQ" #2. Figure 9.HF-18. Figure 9.HF-19. Figure 9.HF-20. Figure 9.HF-21. Figure 9.HF-22. Figure 9.HF-23. Figure 9.HF-24. Figure 9.HF-25. Figure 9.HF-26. Figure 9.HF-27. Figure 9.HF-28. Figure 9.HF-29. Figure 9.HF-30. Histogram showing frequency of permeabilities in core samples from the Humble State University wells "AX" #1, "S" #2, and "BQ" #2 representing the reef/reef flank apron facies of the W400-W500 interval. Crossplot of core porosity and permeability in the Humble State University "BQ" #2 well, a producer in Hutex Field. Distribution of core permeability for samples from the Humble State University "BQ" #2 well representing the forereef/open shelf facies of the W400-W500 interval. Histogram showing frequency of permeability in core samples from the Humble State University "BQ" #2 well representing the forereef/open shelf facies of the W400-W500 interval. Distribution of core permeability for samples from the Humble State University "R" #3 well representing the reef/ reef flank apron facies of the W300-W400 interval. Histogram showing frequency of permeability in core samples from the Humble State University "R" #3 well representing the reef/reef flank apron facies of the W300-W400 interval. Lease locations in the Hutex and Magutex fields for those leases where oil production was analyzed. Producing water/oil ratio (WOR) plotted against cumulative oil recovery for selected leases producing from the W400-W500 interval in Hutex and Magutex fields. Initial water/oil ratio in the Hutex Field area. Data are from operatorreported initial potential test results. Initial oil flow rate from producing wells at Hutex and Magutex fields. Crossplot of the test flow rate (BOPD) at initial well completion versus flow capacity (k x h, and-ft). Crossplot of ultimate oil recovery per porosity-foot of pay (MBO/ x h ft) as a function of the gross pay thickness from top-wristen to the oil/water contact. Crossplot of ultimate oil recovery per porosity-foot of pay (MBO/ x h ft) as a function of the subsea depth of the lowest perforation relative to the oil/water contact. xx

26 Figure 9.HF-31. Figure 9.HF-32. Crossplot of ultimate oil recovery per well as a function of porosity-feet of pay from top-wristen to oil/water contact. Production decline curves for two types of Hutex wells. MOUND LAKE FIELD Figure 9.MLF-1. Figure 9.MLF-2. Figure 9.MLF-3. Figure 9.MLF-4. Figure 9.MLF-5. Figure 9.MLF-6. Figure 9.MLF-7. Figure 9.MLF-8. Figure 9.MLF-9. Figure 9.MLF-10. Figure 9.MLF-11. Figure 9.MLF-12. Figure 9.MLF-13. Figure 9.MLF-14. Figure 9.MLF-15. Figure 9.MLF-16. Location of Mound Lake Field in relation to the Fusselman truncation edge and major structural features. Index map of Mound Lake Field area showing locations, API numbers, and initial status of Fusselman penetrations. Drilling dates and initial potential figures for wells in Mound Lake Field (including Mound Lake North Field). Type log for Mound Lake Field showing stratigraphic units, wireline-log character, and core-to-log comparison for cored interval. Isopach map of the Sylvan Shale, Mound Lake Field area. Isopach map of Fusselman Formation, Mound Lake Field area. Isopach map of the Woodford Shale, Mound Lake Field area. Isopach map of the lowermost Woodford Shale (WDFDB-UNCON), Mound Lake Field area. Thinsection photomicrographs of samples from the Fusselman Formation in Mound Lake Field. Structure map contoured on the top of the Sylvan Shale. Structure map contoured on the top of the Fusselman Formation (pre- Woodford unconformity). Crossplot of core porosity and sonic transit time for the Fusselman reservoir in five wells from Mound Lake Field. Crossplot of porosity and permeability determined from analysis of core plugs from the Fusselman in selected producing wells. Distribution of core permeability for Fusselman samples ranked from highest to lowest values by percentile. Histogram showing frequency of permeability in core samples arranged in groupings defined by the logarithm of permeability. Distribution of core permeability (k) for Fusselman samples arranged from high k to low k by percentile for four individual wells. xxi

27 Figure 9.MLF-17. Figure 9.MLF-18. Figure 9.MLF-19. Crossplot of recovery factor (ultimate oil recovery per porosity-ft of pay or MBO/ x h ft) as a function of the subsea depth of the base of the Woodford Shale for three leases completed early in Mound Lake Field development. Crossplot of water/oil ratio (WOR) plotted against cumulative oil recovery per well of the early Fusselman producers in Mound Lake Field. Production curves for three leases at Mound Lake Field. WALKER FIELD Figure 9.WF-1. Figure 9.WF-2. Figure 9.WF-3. Figure 9.WF-4. Figure 9.WF-5. Figure 9.WF-6. Figure 9.WF-7. Figure 9.WF-8. Figure 9.WF-9. Figure 9.WF-10. Figure 9.WF-11. Figure 9.WF-12. Figure 9.WF-13. Figure 9.WF-14. Location of Walker Field in relation to major structural features in the GDI study area. Index map of Walker Field showing well locations, API numbers, and initial status of Silurian wells. Portion of a north-south seismic line across Walker Field showing the high-angle fault that bounds the field. Structure map of the Walker Field area contoured on the top of the Wristen Formation. Isopach map of the Wristen Formation at Walker Field. Sequence diagram showing the major events that produced the variable thicknesses of Wristen section associated with the Walker Field structure. Isopach map of the lower Woodford Shale (WDFDB-UNCON). Type log for Walker Field showing stratigraphic units, wireline-log character, core-to-log comparison for cored interval, and depositional facies. Core photographs of Silurian rocks in Walker Field. Crossplot of Sidewall Neutron (SNP) porosity and sonic transit time. Crossplot of sonic transit time and core porosity. Crossplot of Sidewall Neutron (SNP) porosity and core-derived porosity suggests a significant chert component in the rock matrix. Crossplot of core porosity and permeability for the Pan American Seagler "A" #1 well, a subcommercial downdip producer in Walker Field. Distribution of core permeability from highest to lowest for the Pan American Seagler "A" #1. xxii

28 Figure 9.WF-15. Figure 9.WF-16. Figure 9.WF-17. Figure 9.WF-18. Histogram showing log normal distribution of permeability in core samples from Walker Field. Crossplot of ultimate oil recovery per porosity-foot of pay (MBO/0 x h foot) as a function of subsea depth of the lowest perforation (by well or lease average) relative to the oil/water contact at feet subsea. Crossplot of water/oil ratio (WOR) and cumulative oil recovery per well. Production curve for an average Walker Field well. Initial production averaged 194 BOPD with ultimate production of 203 MBO/well. Recovery was 91 MBO/porosity-foot (1400 BO/acre-ft). PETERSON SOUTH FIELD Figure 9.PSF-1. Figure 9.PSF-2. Figure 9.PSF-3. Figure 9.PSF-4. Figure 9.PSF-5. Figure 9.PSF-6. Figure 9.PSF-7. Figure 9.PSF-8. Figure 9.PSF-9. Figure 9.PSF-10. Location of Peterson South Field relative to major structural provinces in the study area. Index map of the study area showing the location and initial status of pre- Pennsylvanian wells. Structure map contoured on the top of the Montoya, the producing interval in Peterson South Field. Structure map contoured on the top of the Fusselman Formation. Type log for the pre-pennsylvanian section at Peterson South Field. Wireline-log characteristics of the cored interval of the Montoya Group at the Phillips Lambirth "A" #2 well. Map showing thickness of the Montoya Group, the limit of Montoya subcrop beneath the Pennsylvanian erosion surface, and the erosional truncation edge of the Montoya Group in the study area. Map showing thickness and the erosional truncation edge of the Fusselman Formation in the study area. Core photographs of Montoya rocks in Peterson South Field. Core photographs of an exposure profile within Montoya and post- Montoya rocks from Peterson South Field. Figure 9.PSF-11. Crossplot of core porosity and permeability in the Phillips Lambirth "A" #2 well, a Montoya producer in Peterson South Field. Figure 9.PSF-12. Distribution of core permeability for samples from the Phillips Lambirth "A" #2 well. Permeability variation (V) = 0.94, indicating a very heterogeneous distribution. xxiii

29 Figure 9.PSF-13. Figure 9.PSF-14. Figure 9.PSF-15. Figure 9.PSF-16. Figure 9.PSF-17. Figure 9.PSF-18. Figure 9.PSF-19. Figure 9.PSF-20. Figure 9.PSF-21. Figure 9.PSF-22. Figure 9.PSF-23. Figure 9.PSF-24. Figure 9.PSF-25. Figure 9.PSF-26. Figure 9.PSF-27. Histogram showing frequency of permeability in core samples arranged in classes defined by the logarithm of the permeability. Crossplot of neutron-density porosity and core-derived porosity showing the difference between these two types of porosity measurements. Crossplot of neutron and density log porosity data. The lithology of Montoya strata is calculated by linear interpolation between dolomite and sandstone (chert) end members. Crossplot of sonic transit time and core-derived porosity. Crossplot of neutron-density porosity versus sonic transit time. Typical log response for a well near the updip erosional limit of the Montoya Group where thinning due to truncation and clay infiltration (indicated by higher gamma-ray activity) related to karsting significantly decrease porosity. Crossplot of ultimate oil recovery per well as a function of porosity-feet of pay in the Montoya. Water/oil ratio (WOR) plotted against cumulative oil recovery for selected leases of the Montoya reservoir in Peterson South Field. Statistical distribution of ultimate oil recovery per well in Peterson South Field. Contour map of ultimate oil recovery per well from the Montoya in Peterson South Field. Map of thickness of beds with 4% porosity in the Montoya Group. Porosity increases fairly uniformly away from the erosional truncation edge of this interval. Oil production history and extrapolation of decline to economic limit for the Enserch Lambirth #1 well, a good producer at a high structural position. Oil production history and extrapolation to economic limit for the Phillips Lambirth "A" #2 well, a "better than average" well in the field. Oil production history and extrapolation of decline to economic limit for the Phillips "A" #4 well, a poor well with average structural position but a low set of perforations. Oil production curve for a Fusselman producer in Peterson Field showing rapid water breakthrough that limits ultimate recovery to 175,000 BO (GOR = 570 SCF/STBO) from 8.7 porosity-feet of pay (recovery factor = 20,000 BO/ x h ft). xxiv

30 Figure 9.PSF-28. Production curve for an average Montoya well in Peterson South Field. For the first 5 years, the well experienced hyperbolic decline from an initial rate of 160 BOPD and thereafter declined at 15% per year to an ultimate oil of 180,000 BO/well in 14.3 years. LANGLEY DEEP FIELD Figure 9.LDF-1. Figure 9.LDF-2. Figure 9.LDF-3. Figure 9.LDF-4 Figure 9.LDF-5. Figure 9.LDF-6. Figure 9.LDF-7. Figure 9.LDF-8. Figure 9.LDF-9. Figure 9.LDF-10. Figure 9.LDF-11. Figure 9.LDF-12. Figure 9.LDF-13. Figure 9.LDF-14. Figure 9.LDF-15. Location of Langley Deep Field in relation to major structural provinces in the Permian Basin. Index map of Langley Deep Field showing location and completion dates of wells drilled. Structure map contoured on the pre-woodford unconformity. Contours are based on interpretation of seismic data (Henderson and others, 1984). West-to-east pre-permian structural cross section showing position of the Langley Field anticline on the east flank of the Delaware Basin. Type log for Langley Deep Field showing stratigraphic markers and wireline-log character tied to a cored interval from the producing zone. Portion of the type log for Langley Deep Field comparing wireline-log character and computed lithology in the producing intervals. Stratigraphic cross section A-A' showing lateral and vertical facies relationships in the producing intervals of the Wristen in Langley Deep. Photographs of grainstones from Langley Deep Field. Photographs of samples from the upper Wristen in Langley Deep Field. Crossplot of neutron and density log data for interbedded lagoonal limestones and platform carbonates of the WRSTN-W300 interval and mobile grainflat grainstones of the W300-W400 interval. Schematic paleogeographic reconstruction showing deposition of the WRSTN-W300 interval at Langley Deep Field. Structural cross section A-A' showing lateral and vertical facies relationships of producing intervals and cores in Langley Deep Field. Crossplot of sonic transit time and core-derived porosity. Crossplot of neutron porosity and core-derived porosity. Crossplot of neutron-density porosity and sonic porosity. xxv

31 Figure 9.LDF-16. Figure 9.LDF-17. Figure 9.LDF-18. Figure 9.LDF-19. Figure 9.LDF-20. Figure 9.LDF-21. Figure 9.LDF-22. Figure 9.LDF-23. Figure 9.LDF-24. Figure 9.LDF-25. Figure 9.LDF-26. Figure 9.LDF-27. Figure 9.LDF-28. Figure 9.LDF-29. Figure 9.LDF-30. Figure 9.LDF-31. Histogram showing separation of CNL and FDC values. Representative log from Langley Deep Field showing evidence for fracturing. Low resistivities and erratic response of the MSFL indicate multiple fractures in the Wristen. Crossplot of core porosity and permeability in the Langley Griffin Comm. #1, a gas producer from the WRSTNW300 interval in Langley Deep Field. Ranking of core permeability for samples in the producing WRSTN-W300 interval at Langley Deep Field. Histogram showing frequency of permeability in core samples from the Griffin Comm. #1 arranged in groups by the logarithm of permeability. Crossplot of core porosity and permeability in the Langley Boren Comm. #1 (W300-W400 interval). Distribution of core permeability for core samples from the W300-W400 producing interval in the Langley Boren Comm. #1. Pores types for the samples are also indicated. Histogram of permeability in core samples from the Langley Boren Comm. #1 arranged in groups defined by the logarithm of permeability. Contour map of porosity-feet (x h) for the perforated interval in each well producing from the Wristen Formation in Langley Deep Field. Contour map of ultimate gas recovery from the Wristen Formation in Langley Deep Field. Contour map of ultimate gas recovery per porosity-feet of pay at Langley Field. Crossplot of ultimate gas recovery per well as a function of porosity-feet of pay over the perforated interval. Production history of the Griffin Comm. #1, a downdip well producing from the WRSTN-W300 interval near the south end of Langley Field. Production history of the Boren Comm. #1, a crestal well producing from the W300-W400 interval in the northwest part of the field. Production curve for gas in an average well in Langley Field showing an initial rate of 100,000 MCF per month with hyperbolic decline to 2.25 BCF (and 239,000 BC) ultimate recovery in 18 years. Crossplot of water/oil ratio (WOR) and cumulative equivalent oil recovery per well for the Griffin Comm. #1 at the south end of the field. xxvi

32 Figure 9.LDF-32. Figure 9.LDF-33. Figure 9.LDF-34. Crossplot of water/oil ratio (WOR) and cumulative equivalent oil recovery per well for the Boren Comm. #1, a good Wristen producer at the north end of the field. Crossplot of water/oil ratio (WOR) and cumulative equivalent oil recovery per well for all other Langley Deep wells. In general, the W300-W400 interval wells produce at higher water/oil ratios than wells producing from the WRSTN-W300 interval. Structural cross section of the Wristen reservoir in Langley Deep Field showing facies, perforations, and a brief description of production for each well. DOLLARHIDE FIELD Figure 9.DHF-1. Figure 9.DHF-2. Typical log from Dollarhide Field showing major lithologic packages and the associated core description of the contact between the Wristen and Thirtyone formations. Photomicrographs of representative samples from the Thirtyone Formation in Dollarhide Field. CONCLUSIONS Figure 9.CON-1. Figure 9.CON-2. Figure 9.CON-3. Figure 9.CON-4. Figure 9.CON-5. Figure 9.CON-6. Figure 9.CON-7. Summary of fields selected for detailed study showing type of production, producing zone, nature of trap, and nature of the overlying reservoir seal. Schematic summary of reservoir lithology, facies, and pore type for the six fields selected for detailed study. Crossplot of ultimate oil recovery per porosity-foot of net pay (recovery factor) versus oil viscosity at initial reservoir conditions for the four oilfields developed on similar well spacing (about 70 acres/well). Crossplot of ultimate oil recovery per acre-foot of pore volume versus initial oil viscosity for five oilfields with natural waterdrive reservoirs. Crossplot of recovery efficiency versus oil viscosity at initial conditions for each field. Field development economics at constant pricing criteria for Walker, Mound Lake, and Langley fields. Field development economics at constant pricing criteria for Walker, Mound Lake, and Langley fields. The ratio of present worth profit at a 15% discount rate divided by the present worth investment discounted at 15% on the vertical axis is plotted against ultimate oil (or oil equivalent) recovery per well to give "present value index" (PVI). xxvii

33 LIST OF MAPS AND CROSS SECTIONS Maps Study Well Index Map Structure Map Ellenburger Group Isopach Simpson Group Isopach Montoya Group Isopach Sylvan Shale Isopach Siluro-Devonian Carbonate Units (Fusselman, Thirtyone, Wristen Formations) F900-SLVN Isopach of the Fusselman Formation F500-SLVN Isopach of the Fusselman Formation FSLM-F500 Isopach of the Fusselman Formation W700-FSLM Isopach of the Wristen Formation W600-W700 Isopach of the Wristen Formation W500-W600 Isopach of the Wristen Formation W400-W500 Isopach of the Wristen Formation W300-W400 Isopach of the Wristen Formation WRSTN-W300 Isopach of the Wristen Formation Thirtyone Formation Isopach Woodford Shale Isopach Map WDFD-WDFDB Isopach Map of the Woodford Shale Woodford B-PreWoodford Unconformity Interval Isopach Map PreWoodford Unconformity Subcrop Map Fusselman Formation Isopach Map (FSLM-SLVN) Wristen Formation Isopach Map (WRSTN-FSLM) Regional Cross Sections A-A (3 Sheets) B-B (3 Sheets) C-C (3 Sheets) D-D E-E V-V (2 Sheets) W-W X-X (2 Sheets) Y-Y (2 Sheets) Z-Z (2 Sheets) xxviii

34 Field Cross Sections Brahaney Field A-A Hutex Field A-A, B-B, C-C, D-D Mound Lake Field A-A, A -A, B-B Walker Field A-A, B-B, C-C Peterson Field A-A,B-B Key Well Panels (2) xxix

35 Siluro/Devonian of the Northern Tobosa Basin Selected Figures from the Study

36 Figure S.3. Tectonic elements of the Permian Basin area. Collision and suturing of the continents of Gondwana and Laurussia resulted in a period of intense orogenic activity that produced the Marathon Ouachita Orogenic Belt, and transformed the Tobosa Basin into the Permian Basin. Subsequent uplifting of the Central Basin Platform bifurcated the Tobosa Basin into two discrete sub-basins, the Midland Basin and the Delaware Basin. Return to Text

37 Figure 7.1. Paleobathymetric curve for southern Andrews County. This curve was constructed based upon the recognition of types of unconformities (Type 1 or 2), hinge line progradations, and facies relationships. Major sequence boundaries occur at the Ellenburger/Simpson and Thirtyone/Woodford boundaries. Return to Text Page 7-2 Return to Text Page 7-21

38 Figure 9.HF-9. Fence diagram showing lateral and vertical facies relationships and the relation of facies to production at Hutex and Magutex fields. Return to Figure 9.HF-16 Return to Text Page 9-HF-6 Return to Text Page 9-HF-7

39 Figure 9.DHF-2E. Silicified zones within the upper reservoir interval show that peloids are a common allochem and that the original lithologies were most likely peloid packstones and grainstones. Silicified zones appear yellow and blue in this photograph taken with a gypsum plate. The dolomitized matrix-appears purple. Figure 9.DHF-2F. The sandy dolomite of the upper reservoir interval may contain up to 10% glauconite, visible here as blue-green pellets. Note that the detrital quartz (white) is bimodally sorted, with larger subrounded grains and smaller angular (windblown?) Particles. Return to Text

40 Example of a Core Description