U.S. Shale Gas From Resources and Reserves to Carbon Isotope Anomalies John B. Curtis Potential Gas Agency Colorado School of Mines
Major U.S. Basins and Shale Plays c. 2007 (Where are the Haynesville and Marcellus???)
Shale Gas Annual Production and Energy Information Administration (EIA) Forecast 2,500 CUM EIA Projection Annual Production, Bcf 2,000 1,500 1,000 500 0 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2015 2017 2019 2021 2023 2025 2027 2029 EnCana
U.S. Shale Gas Annual Production from Five Classic Plays to 2007 Annual Production, Bcf 1,200 1,000 800 600 400 New Albany Lewis Barnett Antrim Ohio Expiration of Section 29 Tax Credit 200 0 EnCana 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 Modified and updated from Hill and Nelson, 2000
Targeted Research $150 Million
Acquisitions >$8 Billion Source: Trollart.com Ray Troll
Resource Development >$15 Billion Source:AAPG Source:devonenergy.com Source:chiefoiland gas.com Source:AAPG Source:devonenergy.com
Hydrocarbons From Shale Never Say Die Growth in Barnett Shale - Ft. Worth Basin 600 Gas Production Well Count 5,000 4,500 Annual Production, Bcf 500 400 300 200 100 4,000 3,500 3,000 2,500 2,000 1,500 1,000 500 Producing Wells 0 0 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004
Exploration Considerations Natural fractures - Friend or Foe? Facies changes - greater permeability Kerogen type - I,II,IIS,III Microbial or thermogenic gas? Thermal maturation history MWD - especially w/ gas isotopes
Geochemical Properties of Gas Shales Modified from Hill and Nelson, 2000
Evolution of Antrim Shale Gas Modified from original work by Ira Pasternack
Some Elements of a Successful Shale Gas Play Organic Richness Maturation Thickness Gas-In-Place Productivity Mineralogy Permeability Brittleness Pore Pressure
Potential Supply of Natural Gas in the United States Report of the Potential Gas Committee (December 31, 2008)
Proved Reserves vs Resources Known gas reservoirs Discovered Existing economic conditions Existing operating conditions Undiscovered Effects of technology Effects of economics POTENTIAL GAS AGENCY COLORADO SCHOOL OF MINES
Regional Resource Assessment Traditional Coalbed Total U.S. 1,673.4 Tcf 163.0 Tcf 1,836.4 Tcf 51.3 2.6 374.4 51.9 24.0 16.6 353.5 17.3 193.8 57.0 274.9 7.5 455.2 3.4 Data source: Potential Gas Committee (2009)
PGC Resource Assessments, 1990-2008 Total Potential Gas Resources (mean values) Data source: Potential Gas Committee (2009)
Possible Constraints on Future Gas Supply Resource Base Gas Price Environmental Concerns Skilled Workforce Sufficient Supply to Meet Demand Technology Pipeline Capacity Regulatory & Land Issues Rig Availability
Gas Character Anomalies Found in Highly Productive Shale Gas Wells John E. Zumberge 1 Kevin A. Ferworn 1 John B. Curtis 2 1 GeoMark Research Ltd., Houston, Texas USA 2 Colorado School of Mines, Golden, Colorado USA
Presentation Outline Background: carbon isotope fractionation; gas wetness and wellsite sample collection during drilling; I. Ethane isotope rollover, suggestive of in situ gas cracking and more productive wells; II. Mud gas isotope reversals, indicative of overpressured shales; III. Permeability markers from differences in methane isotopic composition between mud (free) and cuttings (adsorbed) gases.
Background
Dry Gas and Wet Gas Compositions
Wellsite Sampling for Gas Isotopes IsoTube for mud gases mud gas sampling manifold IsoJar for cuttings gases
Mud Gas and Cuttings Sampling
Changes in Carbon Isotope Ratios with Thermal Maturation (after M. Schoell) After M. Schoell
I. Barnett Shale Ethane Isotope Rollover C 2 isotope rollover Normal increasing maturity trend Ethane isotope reversals in mature eastern Barnett gases
Barnett Ethane Isotope Rollover Normal maturity trend Ethane isotope reversal
Stabilized Production vs Wetness 35,000 Stabilized Production vs. Gas Wetness 30,000 Poorly producing rollover wells are often earlier completions. Low TOC and rock properties are also important issues. Stabilized Production (mscf/month) 25,000 20,000 15,000 10,000 C2 Isotope Rollover Wells without isotope rollover are never the best producers. 5,000 0 0 5 10 15 20 25 Gas Wetness (C2+)
Summary - Ethane Isotope Rollover Ethane (and propane) isotope rollover occurs in increasingly high-maturity shale-gas wells. Behavior is also observed in numerous other gas shales in other basins. These wells appear to be among the most productive shale-gas wells:? In situ cracking increases the number of smaller molecules, increasing fluid pressure.? Organic material becomes more brittle, leading to increased kerogen porosity and permeability.
II. Mud Gas Ethane Isotope Reversals Haynesville Example 5,000 5,000 6,000 6,000 7,000 7,000 8,000 8,000 Bossier / Cotton Valley Haynesville Measured Depth, MD (ft) 9,000 10,000 11,000 Measured Depth, MD (ft) 9,000 10,000 11,000 top of overpressure 12,000 12,000 13,000 13,000 14,000 14,000 normal maturity isotopic trend 15,000 0 4 8 12 Wetness, (C2 - nc5) / (C1 - nc5) 15,000-40 -35-30 -25-20 Ethane Carbon Isotope, δ 13 C ( )
Barnett Shale Stratigraphy
Eas t Texas /North La. Oil Dis tribution Haynesville East Texas Field Haynes ville-bossier Jurassic Carbonate Source Jurassic/Cretaceous Reservoirs Cretaceous Shale Source Cretaceous Reservoirs Tertiary Shale Source & Reservoir
III. Shale Gas Isotopes as Permeability Markers 4,200 4,300 4,400 Headspace Gas - IsoJars Mud Gas - IsoTubes A clear isotopic difference exists between methane from mud gases (black squares) and methane from headspace gases (red squares). Mud gas ~ Free / solution / lost gas Measured Depth 4,500 4,600 4,700 Headspace gas ~ Adsorbed gas Larger differences between IsoTube And IsoJar isotopes correlate with increased permeability. 4,800 4,900 More Free Gas More Adsorbed Gas -50-45 -40-35 -30 Methane Carbon Isotope
Well Log Evidence for Porosity/Permeability Detection from Shale Gas Isotopes 1 dt 2 3 4 GR NPOR LM (AT10_) ISOJARS DEPTH 0 GAP 150 0.45 V/V -0.15 0.2 2000-50 -20 SP DPHI LM AT20 ISOTUBES -500 MV -300 0.45 V/V -0.15 0.2 CHMN 2000-50 -20 Zones of maximum porosity / permeability
Shale Gas Analyses as Permeability Markers Poorer Permeability 4,200 4,300 Headspace Gas - IsoJars Mud Gas - IsoTubes Mud Gas 4,400 Measured Depth 4,500 4,600 4,700 Headspace Gas Poorer permeability: Gas eventually evolving off cuttings has more free gas, making methane isotopes more negative. 4,800 More More Free Adsorbed Gas Gas 4,900-50 -45-40 -35-30 Free Gas (more negative isotopes) Methane Carbon Isotope Adsorbed Gas (more positive isotopes)
Shale Gas Analyses as Permeability Markers Better Permeability 4,200 4,300 Headspace Gas - IsoJars Mud Gas - IsoTubes Mud Gas 4,400 Measured Depth 4,500 4,600 Headspace Gas Better permeability: Gas eventually evolving off cuttings is mostly adsorbed gas. 4,700 4,800 More More Free Adsorbed Gas Gas 4,900-50 -45-40 -35-30 Free Gas (more negative isotopes) Methane Carbon Isotope Adsorbed Gas (more positive isotopes)
Conclusions Shale-gas well performance can be correlated to gas character anomalies seen in produced, mud and headspace gas isotopic analyses: Ethane and propane isotope rollovers indicate in situ cracking at high maturities. Ethane isotope reversals within a single well demonstrate overpressure/effective seals. Mud (free) and headspace (adsorbed) methane isotopic signatures can be used as permeability markers.
Potential Gas Agency
Regional Resource Assessment Summary Traditional Coalbed Gas Total Pot. Region s Resources Resources Resources Proportion PGC Area (Mean, Tcf) (M.L., Tcf) (Tcf) of Total L48 Gulf Coast 455.2 3.4 458.5 28.1% Rocky Mountain 374.4 51.9 426.3 26.1% Atlantic 353.5 17.3 370.8 22.7% Mid-Continent 274.9 7.5 282.4 17.3% Pacific 51.3 2.6 53.8 3.3% North Central 24.0 16.6 40.6 2.5% Total Lower 48* 1,484.9 99.2 1,632.5 Alaska 193.8 57.0 250.8 Total U.S. (means)* 1,673.4 163.0 1,836.4 Data source: Potential Gas Committee (2009) * Separately aggregated total, not arithmetically additive.
Regional Resource Comparison Data source: Potential Gas Committee (2009)
PGC Resource Assessment 2008 Total Traditional Resources (mean values) by category Probable Resources Speculative Resources Possible Resources Probable (existing fields) 441.4 Tcf Possible (new fields) 736.9 Tcf Speculative (frontier) 500.7 Tcf Total 1,673.4 Tcf Data source: Potential Gas Committee (2009)
PGC Resource Assessment 2008 Total Coalbed Gas Resources (mean values) by category Probable Resources Possible Resources Speculative Resources Probable (existing fields) Possible (new fields) Speculative (frontier) Total 14.2 Tcf 49.8 Tcf 98.9 Tcf 163.0 Tcf Data source: Potential Gas Committee (2009)