Simulation of Shale Gas Reservoirs Incorporating Appropriate Pore Geometry and the Correct ...

297 Pages·2014·6.78 MB·English

Final Reportt to

SIMUULATIOON OF SHHALE GGAS RESSERVOIRRS
INCOORPORAATING AAPPROPPRIATEE PORE GGEOMEETRY ANND
THHE CORRRECT PHHYSICS OF CAPPILLARIITY ANDD FLUIDD
TRAANSPORRT
Prroject 099122.111.FINAL

Septeember 7, 20114
Deepakk Devegowdaa, Faruk Civaan, Richard Siigal
Boarrd of Regentss, University of Oklahomaa
2001 David L. Boren Blvd, 3 Partners Plaace, Norman,, OK 73019
Phone: [phone]
Website: http://ors.ou.edu
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LEGAL NOTICE

This report was prepared by The Board of Regents, University of Oklahoma as an account
of work sponsored by the Research Partnership to Secure Energy for America, RPSEA.
Neither RPSEA members of RPSEA, the National Energy Technology Laboratory, the U.S.
Department of Energy, nor any person acting on behalf of any of the entities:

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ALL DAMAGES RESULTING FROM THE USE OF, ANY INFORMATION,
APPARATUS, METHOD, OR PROCESS DISCLOSED IN THIS DOCUMENT.

THIS IS A FINAL REPORT. THE DATA, CALCULATIONS, INFORMATION, CONCLUSIONS,
AND/OR RECOMMENDATIONS REPORTED HEREIN ARE THE PROPERTY OF THE U.S.
DEPARTMENT OF ENERGY.

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ABSTRACT
In the last decade, production of hydrocarbons from organic rich shale reservoirs has
exploded onto the world energy landscape. These unconventional reservoirs are now
recognized as forming an abundant worldwide resource that has already significantly
changed the face of the energy landscape in the United States. Initially, production from
these reservoirs was mainly dry gas, but exploration and development activity has largely
moved to production of condensates and oils in many parts of the continental United
States. The focus in this chapter is the modeling and simulation of transport and storage in
shale reservoirs.
The economic development of shale reservoirs is largely attributed to the
introduction and maturation of two technologies: massive hydraulic fracturing and long
reach horizontal wells. Because of the very low permeability of shales, these completion
and drilling schemes are considered to be the predominant reasons for the successful
development of shale and tight gas and oil resources in the US. In general, because of the
ultra‐low permeability of shales, the well architecture and the fracture geometry, including
the hydraulic fracture and re‐activated natural fracture networks, produced by the
stimulations are considered to completely define well drainage volumes within the
reservoir.
The very low matrix permeability of the shale reservoir rocks is a consequence of a
pore geometry that includes pores less than an order of magnitude larger than a methane
molecule. Studies have shown that pore proximity effects in nanopores can potentially alter
the behavior of reservoir fluids. Fluid phase behavior and transport deviate significantly
from the corresponding formulations for conventional rocks that are characterized by
significantly larger pores. Under some conditions, the molecule‐wall interactions tend to be
more important than the inter‐molecular interactions within the fluid that have
traditionally formed the basis of quantifying fluid PVT properties, transport and storage.
For shales, however, the small size of the pores restricts the pore to contain only a
relatively few molecules whose behavior in this confined environment may be too complex
to describe using classical thermodynamics.
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Organic shale reservoirs by their nature contain significant volumes of organic
material and have matured enough to produce and expel large volumes of hydrocarbons.
They therefore have both a complex wettability structure, support significant hydrocarbon
storage in an adsorbed state on some pore walls, and at some stage in their evolution had
extensive natural fracture systems produced by the process of expelling the hydrocarbons.
For a simulator to fully capture the complexity of organic rich shale reservoirs, it must
accommodate potentially two fracture systems with different properties, and at least two
pore systems with dramatically different wettability character and pore size distributions.
The connectivity of these various reservoir components will differ among reservoirs and
often may not be well known so must remain a parameter that can be adjusted in history
matching. Besides a more complex micro‐geometry at a minimum the equations that define
hydrocarbon storage, transport, and the equations of state must be modified, the
assumption of instantaneous capillary equilibrium must be relaxed, and parameters such
as permeability and porosity will be explicit functions of pore pressure, not just effective
pressure.
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TABLE OF CONTENTS
ABSTRACT ................................................................................................................................................................. IV 
TABLE OF CONTENTS .......................................................................................................................................... VI 
LIST OF FIGURES .................................................................................................................................................... XI 
LIST OF TABLES ..................................................................................................................................................... XX 
EXECUTIVE SUMMARY .................................................................................................................................... XXII 
CHAPTER 1: SIMULATION OF SINGLE‐COMPONENT GAS TRANSPORT IN SHALES ................. 1 
1.1. Rarefication and slippage effects on gas flow ................................................................................. 1 
1.1.1. Mean free path of natural gases .................................................................................................... 1 
1.1.2. Gas flow in extremely narrow capillaries ................................................................................. 6 
1.1.3. Gas flow through extremely‐low permeable media .......................................................... 10 
1.2. Results and discussion ........................................................................................................................... 16 
1.2.1 Impact to producers ......................................................................................................................... 20 
1.3 Conclusions .................................................................................................................................................. 22 
CHAPTER 2: CAPILLARY NON‐EQUILIBRIUM FOR GAS‐WATER FLOWS IN NANOPOROUS
SHALES ....................................................................................................................................................................... 23 
2.1 Non‐instantaneous capillary equilibrium ....................................................................................... 23 
2.1.1. Transient behavior in Cylindrical Capillary Tubes ............................................................ 24 
2.1.2. Relaxation of Saturation, Capillary pressure, and Relative Permeability ................ 26 
2.1.3. Modeling Water Displacement by Gas .................................................................................... 30 
2.2. Modeling the Relaxation Phenomenon in Reservoir Simulators ......................................... 35 
2.3 Correlation of Relaxation Time in Imbibition and Drainage Processes ............................. 36 
2.4 Results and Discussion: Effect of Relaxation on Transient Fluid Displacement ............ 40 
2.4.1 Impact to Producers ......................................................................................................................... 43 
2.5 Conclusions .................................................................................................................................................. 44 
CHAPTER 3: EFFECT OF PORE PROXIMITY ON FLUID BEHAVIOR AND PRODUCTION
TRENDS IN SHALE GAS‐CONDENSATE RESERVOIRS ........................................................................... 45 
3.1 Introduction ................................................................................................................................................. 45 
3.2 Behavior of Fluids in Nanoporous Confinement .......................................................................... 48
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3.3 Effects of confinement on critical properties ................................................................................ 49 
3.3.1 Extension of critical property variations to other hydrocarbon species .................. 53 
3.3.2 Effects of confinement on real gas deviation factor ........................................................... 55 
3.4 Effect of confinement on phase behavior of gas‐condensate fluids .................................... 56 
3.5 Results and Discussion: Gas Condensate Well Performance under the Effects of Pore
Proximity .............................................................................................................................................................. 62 
3.5.1 Impact to Producers ......................................................................................................................... 71 
3.6 Conclusions .................................................................................................................................................. 72 
CHAPTER 4: IMPACT OF ADSORPTION ON MULTI‐COMPONENT FLUID TRANSPORT IN
SHALES ....................................................................................................................................................................... 74 
4.1 Adsorbed Phase Transport .................................................................................................................... 74 
4.2 Capillary Tube Model ............................................................................................................................... 75 
4.3 Single Component Adsorption Isotherm ......................................................................................... 77 
4.4 Gas Flow in a Single Capillary Tube ................................................................................................... 79 
4.4.1 Effective Hydraulic Radius ............................................................................................................ 79 
4.4.2 Free Gas Flow ...................................................................................................................................... 81 
4.4.3 Diffusion in Adsorbed Phase ........................................................................................................ 82 
4.5 Gas Flow in Bundle of Variable Size Capillary Tubes ................................................................. 85 
4.6 Case Study: Gas Flow in a Single Capillary Tube .......................................................................... 85 
4.7 Flow Through Porous Media ................................................................................................................ 86 
4.7.1 Adsorbed Phase Diffusion ............................................................................................................. 89 
4.8 Results and Discussion ............................................................................................................................ 91 
4.8.1 Transport for a Bundle of Variable Size Tubes .................................................................... 91 
4.8.2 Determination of the Equivalent Pore Size ............................................................................ 94 
4.9 Impact to Producers ................................................................................................................................. 98 
4.10 Conclusions ................................................................................................................................................ 99 
CHAPTER 5: MULTI‐COMPONENT AND MULTIPHASE FLUID FLOW IN SHALES .................. 101 
5.1 Multicomponent Adsorption .............................................................................................................. 101 
5.3 Phase Behavior in Nanopores ............................................................................................................ 102 
5.4 Compositional Modeling of Fluid Mixture .................................................................................... 103 
5.6 Phase Behavior of Fluid Confined in Nanopores ....................................................................... 105
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5.7 Results and Discussion: Compositional Variations in Produced Fluids ........................... 109 
5.7.1 Synthetic oil Case Study ............................................................................................................... 109 
5.7.2 Black oil Case Study ........................................................................................................................ 118 
5.8 Impact to Producers ............................................................................................................................... 124 
5.9 Conclusions ................................................................................................................................................ 125 
CHAPTER 6: THE ROLE OF MIXED WETTABILITY, NATURAL FRACTURES, ADSORPTION
AND DIFFUSION ON SHALE WELL PRODUCTIVITY AND HISTORY MATCHING ..................... 127 
6.1 Natural Fractures in Shales ................................................................................................................. 127 
6.2 Wettability of Shales............................................................................................................................... 128 
6.3 The Role of Adsorption and Diffusion in Shale Gas Production .......................................... 129 
6.3.1 Reservoir Simulation Modeling Approaches ........................................................................... 129 
6.3.2 Modeling Basis and Assumptions ............................................................................................ 131 
6.3.3 Effect of Adsorption on Shale Gas Production .................................................................... 136 
6.3.4 Effect of Molecular Diffusion on Shale Gas Production .................................................. 139 
6.4 Results and Discussion: History Matching and Production Data Analysis ..................... 145 
6.4.1 History Matching for Different Simulation Approaches ................................................. 145 
6.4.2 Comparison of the Simulation Modeling Approaches ..................................................... 147 
6.5 Impact to Producers ............................................................................................................................... 158 
6.6 Conclusions ................................................................................................................................................ 160 
CHAPTER 7: THE IMPACT OF PORE SIZE AND KEROGEN MATURITY ON THE BEHAVIOR OF
WATER AND HYDROCARBON IN ORGANIC KEROGEN NANOPORES IN SHALES .................. 161 
7.1 Background ................................................................................................................................................ 162 
7.2 Pore Scale Models of Kerogen ............................................................................................................ 167 
7.2.1 Description of Kerogen Models with Different Degrees of Maturity ........................ 167 
7.2.2 Graphite Slit Pore Model Description ..................................................................................... 169 
7.2.3 Organic Pore Model ........................................................................................................................ 170 
7.2.4 Molecular Interactions for Water and Pore Walls ............................................................ 171 
7.3 Behavior of Water in Organic Pores ................................................................................................ 173 
7.3.1 Pore Filling Effect ............................................................................................................................ 173 
7.3.2 Influence of Surface Roughness on Water Adsorption ................................................... 178 
7.3.3 The Role of Kerogen Maturity on Water Uptake ............................................................... 180
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7.4 Results and Discussion: Kerogen Maturity and the Behavior of Water ........................... 182 
7.5 Dynamics of Water and Octane in Kerogen and Graphite Pores ........................................ 183 
7.5.1 Model Description: Octane and Water in Kerogen Nanopores ................................... 183 
7.6 Results and Discussion .......................................................................................................................... 186 
7.6.1 Behavior of Water and Octane in Kerogen and Graphite Pores .................................. 186 
7.6.2 Behavior of Water: Formation of Water Clusters ............................................................. 192 
7.6.3 Potential Wettability Alternation Due to Surface Activation ....................................... 193 
7.6.4 Presence of Octane and Water in the Kerogen Body ....................................................... 193 
7.6.5 Dependence of Adsorption Characteristics on Surface Roughness ........................... 194 
7.7 Impact to Producers ............................................................................................................................... 198 
7.8 Conclusions ................................................................................................................................................ 198 
CHAPTER 8: EFFECTIVE UPSCALING OF HETEROGENEOUS NANOSTRUCTURES IN SHALE
POROUS MEDIA .................................................................................................................................................... 200 
8.1 Shale Petrophysics for Flow Simulations ...................................................................................... 205 
8.1.1. Heterogeneity and Connectivity .............................................................................................. 205 
8.1.2. Adsorption......................................................................................................................................... 207 
8.1.3. Nanofluidics ...................................................................................................................................... 208 
8.2 Upscaling arrangements of shale nanostructures into a REV .............................................. 210 
8.3.1 Simulation Setup for Upscaling Nanostructures to REV ................................................ 212 
8.3.2. Validation of the Simulation Setup ......................................................................................... 214 
8.3.3. Upscaling Heterogeneity and Connectivity ......................................................................... 217 
8.3.4. Upscaling adsorption and flow through nanoporous media ....................................... 225 
8.4 Upscaling Arrangements of Shale REV into Shale Matrix ...................................................... 234 
8.4.1. Simulation setup for upscaling shale REV to reservoir‐scale ..................................... 235 
8.4.2. Upscaling heterogeneous distributions of shale REV’s ................................................. 235 
8.4 Conclusions ................................................................................................................................................ 241 
CHAPTER 9: TECHNOLOGY TRANSFER ACTIVITIES ........................................................................... 243 
9.1 Project Website ........................................................................................................................................ 243 
9.2 Conferences/Workshops ..................................................................................................................... 243 
9.3 Publications ................................................................................................................................................ 244 
9.3.1 Thesis and Dissertations .............................................................................................................. 244
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9.3.2 Book Chapter ..................................................................................................................................... 245 
9.3.3 Refereed Publications ................................................................................................................... 245 
9.3.4 Conference Proceedings ............................................................................................................... 245 
9.3.5 Current Publications in Progress ............................................................................................. 249 
9.3.6 Unpublished Conference Proceedings ................................................................................... 250 
9.3.7 Invited Seminars and Lectures .................................................................................................. 251 
NOMENCLATURE ................................................................................................................................................ 253 
REFERENCES ......................................................................................................................................................... 255