Dakota Sandstone

Moxa Arch and Surroundingof the

Green River Basin

Dakota Sandstones of the Green River Basin Overview

The Dakota sandstones of the Moxa Arch and surrounding Green River Basin remain attractive targets for explorationists in the Rockies. This regional stratigraphic study encompasses an 18,000 square-mile area includes Sublette, Lincoln, Uinta, Sweetwater, and portions of Teton and Fremont counties in Wyoming; portions or all of Summit, Duchesne, Daggett, and Uintah counties in Utah; and Moffatt County, Colorado. The project, representing more than seven man-years of geologic research, used 1318 wells to evaluate the sequence stratigraphic framework of the Dakota and Muddy formations in the Greater Green River Basin. Along the trend of the Moxa Arch, every well that penetrated the Dakota section was included in the study database. In the surrounding area, at least one well per section, where available, was selected for regional correlations.

Stratigraphic picks, used to subdivide these formations, were correlated along laterally continuous marker horizons that represent transgressive disconformities or their equivalent flooding surfaces. This produced a time-stratigraphic framework for evaluating the distribution of sandstones and reservoirs. The thickness of gross and porous sandstone (based on reservoir-derived porosity) was determined for each stratigraphic interval. Five regional cross sections document the stratigraphic framework for the Dakota and Muddy formations. In addition, regional maps illustrate gross and net sandstone distribution, the occurrence of reservoir

quality, and reservoir development for the most significant stratigraphic intervals.

Twelve outcrops and cores from 129 wells of the Dakota and Muddy formations in the Greater Green River Basin were described for this study. Lateral and vertical variations in lithologies as well as primary and biogenic sedimentary structures from this database were used to interpret the depositional sequences. This rock database illustrates the relationships among lithology, log response, porosity and permeability, and other log-derived measures of reservoir quality.

The petrographic study of 546 thinsections from 50 cores provided data for interpreting textural and diagenetic characteristics of Dakota and Muddy reservoir lithologies. Specific emphasis of the petrographic study was to determine the compositions of the sandstones, define the diagenetic sequence, and to relate cementation to variations in porosity and permeability.

Two field areas on the Moxa Arch were selected for the characterization of reservoirs from shallow-marine (Swan/Blue Forest area) and fluvial (Lucky Ditch/Henry area) depositional environments. These field studies provide a detailed analysis of reservoir quality and reservoir development. Data in these areas relate core-derived measures to log-derived parameters. Concepts derived in these field areas were applied to the regional evaluation of reservoir potential of the Dakota and Muddy formations in the Green River Basin.

Database

1,318 Study Wells

9 Regional Uphole Stratigraphic Markers

20 Internal Dakota and Muddy Markers

129 Cores Described

546 Thinsections

Maps

Regional Maps (1:132,000)

Isopach Maps

Sandstone Maps

Structure Map

Penetration Map of Study Wells

Field Maps

Isopach Maps

Gross Sandstone Maps

Net Porous Sandstone (>15%) Maps

Structure Maps

Cross Sections

5 Regional Stratigraphic Sections

Field Studies

Swan/Blue Forest area, Luckey Ditch/Henry area

Report Contents

TEXT AND FIGURES - An extensively illustrated report includes discussions, figures, and color plates on: Executive Summary, Regional Setting, Lithofacies, Stratigraphy & Sedimentology, Petrography, Reservoir Quality, Field Studies & Porosity Analysis.

CORE AND OUTCROP DESCRIPTIONS - This section contain descriptions of 129

cores from southwest Wyoming, northeast Utah, and north west Colorado.

STRATIGRAPHIC DATA - This file contains the stratigraphic data (29 formation tops and stratigraphic markers, and net sandstone value) and isopach values, as well as information on well name, operator, location, API number, completion date, datum, and production status for the 1318 study wells.

MAPS & CROSS SECTIONS – These sections contain regional maps including isopach maps, structure maps, net

sandstone maps, and a study well map. There are 5 regional cross sections included as well.

Dakota Sandstonesof the Green River Basin

SUBLETTE

TETON

FREMONT

SWEETWATER

LINCOLN

UINTA

SUMMIT

DAGGETT MOFFAT

WYOMING

UTAH COLORADO

Green River

Rock Springs

Kemmerer

Pinedale

Jackson

Riverton

IDAH

OU

TAH

MILES

240 N

Study Boundary

R 118 WT40N

R 97 WT30N

R 32 WR 8 W

T2N

T2N

T12N

T12N

R 121 W R 97 W

StudyTable of Contents

Dakota Sandstones

Green River Basinof the

TABLE OF CONTENTS

TABLE OF CONTENTS …………….…………………………………………………………… i LIST OF MAPS & CROSS SECTIONS ……………………………………………………….. vii ACKNOWLEDGMENTS ………………………………………………………………………… ix

EXECUTIVE SUMMARY EXECUTIVE SUMMARY

INTRODUCTION …………………………….……………………………..…..…….… E-2 OBJECTIVES ……………………………………………………………………….…… E-2

Methods and Data ………….………………………………………………..…. E-2 REGIONAL SETTING ……..…………………………………………….……………… E-4

Structural Setting …………….…………………………………….………....… E-4 Western Interior Seaway ………………………………….………..……..…… E-4 Regional Stratigraphic Relationships ………….…………………………...… E-5

SEQUENCE STRATIGRAPHY ……..……………………………………………….… E-9 Terminology ………………………………………………………………..……. E-9 Sequence Stratigraphy of Albian Strata …………………………………..…. E-9

STRATIGRAPHY AND SEDIMENTOLOGY-LOWER DAKOTA – THERMOPOLIS SEQUENCE …………………………………………….…….…... E-12

Lower Dakota Stratigraphy ………………………………………….……….... E-12 Sedimentology of Lower Dakota Reservoirs ………………………..….……. E-14

STRATIGRAPHY AND SEDIMENTOLOGY - UPPER DAKOTA - FONTENELLE SEQUENCE …………………………...…...... E-17

Upper Dakota Stratigraphy ……………………………………………….….... E-17 Sedimentology of Upper Dakota Reservoirs …………………………..…….. E-19

STRATIGRAPHY AND SEDIMENTOLOGYMUDDY - SHELL CREEK SEQUENCE ………………………………………………...……… E-21

Muddy Stratigraphy ………………………………………………………......… E-21 Sedimentology of Muddy Reservoirs ……………………………………….... E-25

PETROGRAPHY ………………………………………………………………………... E-26 Cements ……………………………………………………………….………... E-27 Controls on Reservoir Quality ……………………….………………….…….. E-28 Applications ……………………………………………………………………... E-29

RESERVOIR QUALITIES OF FLUVIAL AND MARINE SANDSTONES …………. E-30 Introduction ……………………………………………………………………… E-30 Core Analyses …………………………………………………………………... E-31 Log Derived Measures of Reservoir Quality ………………………..……….. E-31 Calculated Average Core Porosity and Permeability ……………….….…… E-33

CHAPTER 1

INTRODUCTION GENERAL INTRODUCTION …………………………..………………...……………. 1-2 OBJECTIVES OF THE STUDY ……………………………….……………….………. 1-3 METHODS AND DATA ……………………………………….…………………….….. 1-4

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Stratigraphic Database ……………………………………………………..….. 1-4 Regional Cross Sections ……………………………...……………………….. 1-5 Cores and Measured Sections …………………………..……………...…….. 1-5 Petrography ………………………………………………………………………1-6 Detailed Study Areas …………………………………………………………… 1-7

CHAPTER 2 REGIONAL SETTING

INTRODUCTION ………………………………………………………………………… 2-2 DEPOSITIONAL SETTING …………………………………………………...….…….. 2-3

Paleotectonics ………………………………………………………………...… 2-3 Cretaceous Foreland Basin …………………………………..………. 2-3 Paleostructures ………..…………………………………………….… 2-3

Sea Level ……………………………………………………………………..… 2-5 Hydrographic Regime ……………………………………………………….…. 2-6

Waves and Tides ………………………………………………..….…. 2-6 Salinity ………………………………………………………...………… 2-7

REGIONAL STRATIGRAPHIC RELATIONSHIPS …………………………..……… 2-8 Jurassic Morrison Formation …………………………………………...………2-8 Lower Cretaceous Cedar Mountain Formation ………………………….….. 2-9

Utah ……………………………………………………………..…..….. 2-9 Central Wyoming ………………………………………………..…….. 2-11 Wyoming Overthrust Belt ……………………………………….……. 2-13

Moxa Arch Group …………………………………………………………...…. 2-14 Central and Eastern Wyoming …………………..…………………... 2-15 Wyoming Overthrust Belt ………………………….……………..…… 2-18 Uinta Mountains ………………………………….………………….…. 2-20

Mowry Shale ……………………………………………………………..……… 2-21 Upper Cretaceous ………………………………………..………………….…. 2-22

Frontier Formation …………………………………..…………….…… 2-22 Hilliard Shale ……………………………………………………..…….. 2-22

CHAPTER 3

SEQUENCE STRATIGRAPHY INTRODUCTION …………………………………………………………………..……. 3-2

Nomenclature …………………………………………………………………… 3-2 GENERAL CONCEPTS OF SEQUENCE STRATIGRAPHY ………………………. 3-4 SEQUENCE STRATIGRAPHY OF ALBIAN STRATA ………………………………. 3-6

Lower Dakota - Thermopolis Sequence ……………………………………… 3-6 Upper Dakota - Fontenelle Sequence …………………………………..…… 3-7 Muddy - Shell Creek Sequence ………………………………………………. 3-10

OUTCROP STRATIGRAPHY OF ALBIAN STRATA ……………………..………… 3-12 Introduction ……………………………………………………………..…….... 3-12 Bear River Formation - Wyoming Overthrust Belt ………………………….. 3-12

Lower Dakota - Thermopolis Sequence ………………………….….. 3-13

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Upper Dakota - Fontenelle Sequence ……………………………….. 3-14 Muddy - Shell Creek Sequence …………………………………….... 3-16

Dakota Formation - Uinta Mountains ……………………………………….… 3-18 Lower Dakota - Thermopolis Sequence …………………………….. 3-19 Upper Dakota - Fontenelle Sequence ……………………………….. 3-20 Muddy-Shell Creek Sequence ………………………………………... 3-22

CHAPTER 4 STRATIGRAPHY AND SEDIMENTOLOGY OF THE LOWER DAKOTA – THERMOPOLIS SEQUENCE

LOWER DAKOTA STRATIGRAPHY ………………………………………………..… 4-2 Introduction …………………………………………………………………….... 4-2 800 Interval ………………………………………………………………...……. 4-2 700 Interval ………………………………………………………………..……. 4-5 600-650 Intervals ……………………………………………………………..… 4-6

SEDIMENTOLOGY OF LOWER DAKOTA RESERVOIRS …………………..…..… 4-8 Introduction ………………………………………………………………...……. 4-8 Marine Sandstones ….………………………………….………………..……. 4-8

Marine Sandstones in Core ……………………………………..……. 4-8 Marine Sandstones in Outcrop …………………………………….… 4-9 Summary …………………….………………………………………..… 4-11

Fluvial Sandstones ……………………………………………………………... 4-11 Fluvial Sandstones in Core ……………………………………...……. 4-12 Fluvial Sandstones in Outcrop ………………………………………...4-12 Architectural Element Analysis ……………………………………......4-14 Paleohydrology of Lower Dakota Fluvial Systems …………………. 4-19

CHAPTER 5 STRATIGRAPHY AND SEDIMENTOLOGY OF THE UPPER DAKOTA – FONTENELLE SEQUENCE

UPPER DAKOTA STRATIGRAPHY ………………………………………………….. 5-2 Introduction ……………………………………………………………………… 5-2 500 Interval …………………………………………………………………..….. 5-3 300, 320, 340, 360, 380 Intervals ……………….………………….………… 5-5 Upper Dakota Sandstones ………………………………………………..…… 5-7

Upper Dakota B …………………………………………………...…… 5-8 Upper Dakota A …………………………………………………..……. 5-10

SEDIMENTOLOGY OF UPPER DAKOTA RESERVOIRS ………………..……….. 5-12 Introduction ……………………………………………………………………… 5-12 Sandstones in the Fontenelle Tongue …………….……………………..….. 5-12 Upper Dakota Fluvial Sandstones ……………………….……………..…….. 5-14 Upper and Lower Dakota Sandstones Contrasted ………………………….. 5-17

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CHAPTER 6 STRATIGRAPHY AND SEDIMENTOLOGY OF THE MUDDY- SHELL CREEK SEQUENCE

MUDDY STRATIGRAPHY ………………………………………………………..…… 6-2 Introduction ……………………………………………………………………… 6-2 Valley-Fill Model ……………………………………………………………..… 6-3 280 Interval …………………………………………………..……………..….. 6-5 250 Interval ………………………………………………………………….…. 6-6

250 Shoreline …………………………………………………….…… 6-7 250 Lagoon ……………………………………………..…………..…. 6-9 250 Fluvial Systems ………………………………………………...… 6-10 Onlap Limits ………………………………………………………...…. 6-12

200 Interval ………………………………………………………………..…… 6-12 180 Interval ………………………………………………………………..…… 6-14 140 Interval ………………………………………………………………….….. 6-15 120 Interval ………………………………………………………………….…. 6-17

SEDIMENTOLOGY OF MUDDY RESERVOIRS ………………..………….………. 6-18 Introduction …………………………………………………………….……..…. 6-18 Shallow Marine Sandstones ………………………………………………...… 6-19 Fluvial Sandstones …………………………………………….…………….... 6-21

CHAPTER 7 PETROGRAPHY

INTRODUCTION ……………………………………………………………..……….... 7-2 METHODS ……………………………………………………………………………….. 7-3 SANDSTONE COMPOSITION …………………………………………….………….. 7-3 CONTROLS ON RESERVOIR QUALITY ………………..…………….…………….. 7-6

Fluvial Sandstones ……………………………………………………..………. 7-6 Compaction …………………………………………………...……….. 7-6 Clay Cementation ……………………………………………….….…. 7-8 Silica Cementation ………………………………………………..…….7-10 Framework Grain Dissolution ………………………..……………….. 7-11 Framework Grain Alteration ……………………………………...…… 7-12

Marine Sandstones ………………………………………………………...…... 7-15 Compaction ………………………………………………………...….. 7-15 Clay Cementation …………………………………………………..….. 7-16 Silica Cementation ……………………………………………….……..7-17 Framework Grain Dissolution ………………….……………………… 7-18 Framework Grain Alternation …………………………………………. 7-18

DIAGENETIC HISTORY …………………………………………………………..…… 7-18 Meteoric/Compactional Regime ………………………………………………. 7-19 Compactional/Cementation Regime …………………………………….……. 7-19 Thermobaric Regime …………………………………………………….…..….7-20

RESERVOIR QUALITY ………………………………………………………………… 7-23 Fluvial Sandstones ……………………………………………….…………….. 7-24

Lower Dakota …………………………………………………………… 7-24 Upper Dakota …………………………………………………………... 7-25 Muddy Formation - Moxa Arch ………………….………………….... 7-27

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Muddy Formation - Rock Springs Uplift ……………………….…..… 7-28 Synthesis ………………………………………………………..….….. 7-29

Marine Sandstones …………………………………………………..………... 7-31 Muddy Formation ..……………………………………………..……… 7-31

CONCLUSIONS AND APPLICATIONS ………………………….…………………… 7-32

CHAPTER 8 RESERVOIR QUALITIES OF FLUVIAL AND MARINE SANDSTONES

INTRODUCTION ………………………………………………………………………… 8-2 METHODS …………………………………………………………………………….…. 8-2 RESERVOIR QUALITY AND RESERVOIR DEVELOPMENT …………………..… 8-4

Cumulative Development of Porosity and Permeability ………………….… 8-6 Average Core Porosity and Permeability Relationship …………………...… 8-7

LOG-DERIVED MEASUREMENTS OF RESERVOIR QUALITY …………….….… 8-9 Sonic Porosity …………………………………………………………...…….... 8-10 Density Porosity ……………………………………………………………..….. 8-12 Sonic and Density Correction ………………………………………...…….…. 8-13 Average Log Porosity Maps ………………………………………………..…. 8-14 Percent Porous Sandstone ……………………………………..…………...… 8-15 ALPHA Maps ……………………………………………………………………. 8-16

CALCULATED AVERAGE CORE POROSITY AND PERMEABILITY ………….… 8-17 Average Core Porosity …………………………….…………………………… 8-17 Average Core Permeability …………….……………………………..………. 8-19 Predicted Average Core Porosity/Permeability ……..………………….…… 8-20

CONCLUSIONS ……………………………………………………………………..….. 8-20

CHAPTER 9 FORMATION EVALUATION OF THE FLUVIAL SANDSTONES IN THE LUCKEY

DITCH/HENRY FIEDL AREA INTRODUCTION ………………………………………………………………………… 9-2 DISCUSSION …………………………………………………………………..……….. 9-2 CONCLUSIONS ………………………………………………………………..……….. 9-5

CHAPTER 10

FORMATION EVALUATION AND PAY ANALYSIS OF THE FLUVIAL AND MARINE SANDSTONES IN THE LUCKEY DITCH/HENRY AND SWAN/BLUE FOREST FIELD AREAS

INTRODUCTION ……………………………………….……………………………….. 10-2 DISCUSSION ……………………………………………...…………………………….. 10-3

Swan/Blue Forest Field Area ………………………………………………….. 10-4 Luckey Ditch/Henry Field Area …………………………………..…………… 10-5

CONCLUSIONS …………………………………………………………………………. 10-6

v

CHAPTER 11 POROSITY ANALYSIS FROM OPEN HOLE LOGS FOR THE FLUVIAL AND

MARINE SANDSTONES IN THE LUCKEY DITCH/HENRY AND SWAN/ BLUE FOREST FIELD AREAS

INTRODUCTION ………………………………………………………………………… 11-2 DISCUSSION ……………………………………………………………………...…….. 11-2

Density-Neutron Logs ………………………………………………………….. 11-3 Sonic (Acoustic) Logs …………………………………………………….……. 11-6

CONCLUSIONS …………………………………………………………………..…….. 11-7

BIBLIOGRAPHY BIBLIOGRAPHY ………………………………………………………………...……………….. B-2

vi

MAPS

API Location Map - East API Location Map – West 200 Marker-Unconformity 1 Interval Isopach – West 320 Marker-Unconformity 3 Interval Isopach – West M400 Marker Structure – East M400 Marker Structure – West M400 Marker-Unconformity 1 Interval Isopach – East M400 Marker-Unconformity 3 Interval – East 140 Interval-Calculated Reservoir Development - East 140 Interval-Alpha Porous Sandstone/Gross Sandstone - East 140 Interval-Gross Sandstone Isolith – East 180 Interval-Calculated Reservoir Development - East 180 Interval-Alpha Porous Sandstone/Gross Sandstone - East 180 Interval-Gross Sandstone Isolith – East 200 Interval-Calculated Reservoir Development - West 200 Interval-Alpha Porous Sandstone/Gross Sandstone - West 200 Interval-Gross Sandstone Isolith – West 250 Interval-Calculated Reservoir Development - West 250 Interval-Alpha Porous Sandstone/Gross Sandstone - West 250 Interval-Gross Sandstone Isolith – West 700 Interval-Calculated Reservoir Development - East 700 Interval-Alpha Porous Sandstone/Gross Sandstone - East 700 Interval-Gross Sandstone Isolith – East 700 Interval-Calculated Reservoir Development - West 700 Interval-Alpha Porous Sandstone/Gross Sandstone - West 700 Interval-Gross Sandstone Isolith – West Upper Dakota B Interval-Calculated Reservoir Development - East Upper Dakota B Interval-Alpha Porous Sandstone/Gross Sandstone - East Upper Dakota B Interval-Gross Sandstone Isolith – East Upper Dakota B Interval-Calculated Reservoir Development - West Upper Dakota B Interval-Alpha Porous Sandstone/Gross Sandstone - West Upper Dakota B Interval-Gross Sandstone Isolith - West

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CROSS SECTIONS

Cross Section A-A’ (5 Panels) Cross Section B-B’ (4 Panels) Cross Section C-C’ (5 Panels) Cross Section D-D’ (4 Panels) Cross Section E-E’ (3 Panels)

viii

Selected Figuresfrom the Study

Dakota Sandstones

Green River Basinof the

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A. Interpretation of north-south cross section A-A' from the central and southern parts of the Moxa Arch.

Figure 3.1. Schematic regional stratigraphic cross sections of the Moxa Arch group in the greater Green RiverBasin. Three Upper Albian stratigraphic sequences have been defined in this area: Lower Dakota-Thermopolis,Upper Dakota-Fontenelle, and Muddy-Shell Creek. These sections illustrate diagramatically the lithostratigraphicand chronostratigraphic changes that occur in these sequences within the study area. Each schematiccross section relates to a full-scale well-log cross section from the map and cross-section folders of the study.

Return to Text Page 5-5Return to Text Page 3-17

Return to Text Page 3-14Return to Text Page 3-7 Return to Text Page 3-11Return to Text Page 3-8

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E

F

Figure 3.30 (continued). Outcrop examples of common lithofacies found in fluvial sandstones ofthe Lower Dakota sequence in the Uinta Mountain area.

Typical expression of deposits interpreted as passive fill in the Lower Dakota. These sandstones are fine-grained, thinly bedded and ripple laminated. From the Pipeline Road exposure.

Overbank mudstones from the top of the Lower Dakota fluvial sequence at the Pipeline exposure, abruptly overlain here by Upper Dakota fluvial sandstones.

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Figure 3.21. Correlation of Upper and Lower Dakota deposits in the Overthrust Belt of northwestern Wyoming. The transition from shoreline sandstones to continental deposits (as at Emigrant Grave) has previously been interpreted to be a simple regressive facies transition. Based on subsurface correlations and the presence of a lenticular sandstone that sits erosionally over the shoreline sandstones (as at Willow Creek), this contact is interpreted in this report as an unconformity that forms the boundary in these outcrops between the Lower and Upper Dakota sequences.

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Figure 7.17(cont). Thin section photomicrographs illustrating the variations in silica cement ofmarine sandstones of the Swan/Blue Forest Field Area.

C. Precipitation of silica in marine sandstones is controlled in part by the distribution of non-quartz detrital grains. Overgrowths occur in areas between quartz grains, but are inhibited by non-quartz grains, chert and feldspar as shown in these photographs.

D. Precipitation of silica in marine sandstones is controlled in part by the distribution of non-quartz detrital grains. Overgrowths occur in areas between quartz grains, but are inhibited by non-quartz grains, chert and feldspar as shown in these photographs.

D

C

Example of a Core Description