Free Gas Recovery Factor
Gf
43,560 Ahe S g Bg
Reduces to:
(Initial Gf – Final Gf) Initial Gf
zi p f fg 1 pi z
Nomenclature
ffg zi z p pi
fractional free gas recovery, fraction of initial initial z factor, dimensionless z factor at average pressure, dimensionless average pressure, psia initial pressure, psia
Example Barnett Sorbed GIP
• • • • • Average Density: Initial Pressure: Initial Temperature: Total Organic Content: Gas Storage Capacity: 2.58 g/cm3 4,000 psia 205 oF. 4.0 wt. % 86.0 scf/ton
Barnett Adsorbed GIP Computation
Gs 1359.7 Gs 6 Ah 10 1359.7 2.5886.0 0.302 MMscf/acre-ft 6 10
Example Barnett Free GIP
• Average temperature: • Average pressure: • Average porosity: • Average gas saturation: • Gas formation volume factor:
New Petrophysical Model
• Recognizes that the available porosity for free-gas and adsorbed gas storage are interconnected. • Evidence has historically existed in the methods used to measure adsorption isotherms. – Sorbed volume must be accounted for during isotherm analysis as some fraction of the initially determined void volume is consumed with adsorbed gas
Nomenclature
fsg GsL Gci p pL
fractional sorbed gas recovery, fraction of initial Langmuir storage capacity, scf/ton initial gas content or storage capacity, scf/ton average pressure, psia Langmuir pressure, psia
• Drainage Area (A) • Reservoir Thickness (h) • Bulk Density (ρ)
• Total Gas Content (Gst)
•
Indirect Method Assumes Total Gas Storage Capacity = Gst
Adsorbed Gas-in-Place Relationship
Gas-In-Place Estimates
Using Rock and Fluid Data to Evaluate Shale-Oil and Gas Shale Plays
Chad Hartman – Chief Technical Advisor WFT Labs Unconventional Reservoir Services
Example Barnett Sorbed Gas Fraction
Gs 0.302 0.471 Gs G f 0.302 0.339meter Units Barnett Shale GIP/Ah MMscf/acre-ft 0.641 h feet 400 A acres 640 GIP/Ah Bscf/section 164 Well Spacing acres/well 40 GIP/well Bscf/well 10.3 GIP/Ah h A GIP/Ah Well Spacing m /m m 2 km 3 m /section 2 km /well
Kuwait Libya Oman Saudi Arabia United Arab Emirates Iraq
Australia India Malaysia Thailand New Zealand Indonesia
Gas-in-Place Relationship
GIP = 1359.7 A h ρ Gst

Gsc
Units Conversion
43,560 ft per acre 1,359.7 3 32.0368 scf ton per cm g
2
Free Gas-in-Place Volume
Gf
43,560 Ahe S g Bg
Nomenclature
Gf A h free gas volume, scf area of interest, acres productive thickness, feet effective porosity, fraction of bulk volume gas saturation, fraction of void volume formation volume factor, res. vol./ surf. vol
e S ge = (1-Sw-Sa)
Simplified Conceptual Model
Old Methodology
Void space measured by porosity measurement
New Methodology
Void space measured by porosity measurement + Sorbed mass measured by adsorption experiment -
oil
GoD
43,560 Ahe So Rs 5.615Bo
water
GwD
43,560 Ahe Swe Rsw 5.615Bw
Nomenclature
GoD GwD A h dissolved gas volume in oil, scf dissolved gas volume in water, scf area of interest, acres productive thickness, feet e effective porosity, fraction of bulk volume S saturation, fraction of void volume Rs solution gas-liquid ratio, scf/STB B formation volume factor, res. vol./surf. vol. sub o oil sub w water
Gs 1,359.7 A h Gsc

Nomenclature
Gs A h sorbed gas-in-place volume, scf area of interest, acres productive thickness, feet average density, g/cm3 adsorbed gas storage capacity, scf/ton
3 3 3
Lewis Shale 0.0945 400 640 24.2 160 6.05 2.17 122 2.59 8 6.85(10 ) 0.648
8
14.7 122 2.59 9 4.64(10 ) 0.162
8
Adsorbed Gas Recovery Factor
f sg
GsL p 1 Gci pL p
e
Sg Bg
Gas Formation Volume Factor
z T 459.67 psc Bg p zsc Tsc 459.67
reservoir volume / surface volume
Nomenclature
p T z sc pressure, psia temperature, oF real gas deviation factor, dimensionless standard conditions
Dissolved Gas-in-Place Volume
Typically accounted for via adsorption isotherm analysis
Barnett Recovery Factor vs. Pressure
43% 34% 20%
New Pore Scale Considerations to Gas-In-Place Estimates
Pore Scale Considerations
• Using the current industry-standard calculation method to determine total gas volumes in organic rich shale reservoirs results in an overestimated GIP. • We present an improved method which takes into consideration the portion of total available pore volume occupied by the sorbed gas component. • Examples show that this volume can be significant, as much as 40%.