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Gas Desorption Technology Overview
Matt MavorWeatherford Laboratories
[email protected]
- Triple Porosity Gas StorageMicro-Porosity (
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Barnett Gas Storage Capacity
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Diffusion vs. Darcy Flow
( )2g bDq C Cr
Diffusion
( )g g bq k p p Darcy
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Nomenclatureqg gas flow rate, volume/time proportional toD
diffusion coefficient, cm2/secr average diffusion distance, cmC
average concentration g/cm3
Cb boundary concentration, g/cm3
kg permeability to gas, mdp average pressure, kPaapb boundary
pressure, kPaa
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Gas Content Estimate Sources
Pressure Core DesorptionConventional / Wireline Core
DesorptionDrill Cutting Desorption Sidewall Core DesorptionGas
Storage Capacity Computation
Free Gas Storage CapacityAdsorbed Gas Storage Capacity
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Lewis Core
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DesorptionCanister
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Gas Volume Measurement
Measured Gas
Content
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Example Desorption DataMeasured Data in White
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Core Recovery Time Information
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Desorption Time ZeroMud Hydrostatic Pressure = Reservoir
PressureMud Hydrostatic Pressure = Critical Desorption
PressureWhen sample is cored if drilled underbalanced
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Desorption Data CorrectionHead-Space Correction
Gas expansion or contraction inside canisterTemperature
changesAtmospheric pressure / elevation changes
Standard Condition CorrectionTypical standard conditions: 60 oF
and 14.696 psia
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Example Direct Method Graph
2
2 203.1 c
D mr G
=
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Sorption TimeTime to desorb 63% of total gas content, hours
( ) 2
1
3600 15 Dr
=
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NomenclatureD/r2 diffusivity sec-1m slope, scf/ton-hour0.5Gc
total gas content, scf/ton sorption time, hours
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Shale DiffusivityLewis Shale
Diffusivity: 1.7(10-6) to 2.6(10-6) sec-1Sorption Time: 7 to 11
hours
Barnett ShaleDiffusivity: 3.1(10-6) to 4.3(10-6) sec-1Sorption
time: 4.3 to 6 hours
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Roller Mill for Residual Gas
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Core Recovery Time
1
10
100
1,000
0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500
Ret
rieva
l Tim
e (m
inut
es)
Depth (feet)
Wireline Coring Retrieval Conventional Coring Retrieval
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Pressure Core BenchmarksIn
-Situ
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Sorption Isotherm Benchmarks
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Coal Gas Content ErrorsAmbient Temperature Desorption
Measurements-33% to -30% errorDrill Cuttings Instead of Core
Samples-25% ErrorLost Gas Content - Smith & Williams Method-40%
to 14% error (usually low)Lost Gas Content - Amoco Method-31% to
119% Error (usually high)
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Sample History
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Temperature Effects
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Direct Method AssumptionsSpherical sample geometryUniform
initial gas contentConstant diffusivityConstant temperature
diffusionExternal pressure immediately reduced to zero
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Simulated Desorption Conditions
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Simulated Desorption Behavior
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Gas Desorption Technology Overview
Matt MavorWeatherford Laboratories
[email protected]
Gas Desorption Technology OverviewTriple Porosity Gas
StorageBarnett Gas Storage CapacityDiffusion vs. Darcy
FlowNomenclatureGas Content Estimate SourcesSlide Number 7Slide
Number 8Slide Number 9DesorptionCanisterSlide Number 11Gas Volume
MeasurementExample Desorption DataCore Recovery Time
InformationDesorption Time ZeroDesorption Data CorrectionExample
Direct Method GraphSorption TimeNomenclatureShale DiffusivityRoller
Mill for Residual GasCore Recovery TimePressure Core
BenchmarksSorption Isotherm BenchmarksCoal Gas Content ErrorsSample
HistoryTemperature EffectsDirect Method AssumptionsSimulated
Desorption ConditionsSimulated Desorption BehaviorSlide Number
31Slide Number 32Gas Desorption Technology Overview
