FACTORS AFFECTING FORENSIC ANALYSIS AND FACTORS AFFECTING FORENSIC ANALYSIS AND INTERPRETATION OF IMPACTS FROM STRAY GAS INTERPRETATION OF IMPACTS FROM STRAY GAS HYDROCARBONS HYDROCARBONS - PRESSURE, MIXING, OXIDATION, DILUTION PRESSURE, MIXING, OXIDATION, DILUTION Anthony W. Gorody, Ph.D., C.P.G., P.G. Anthony W. Gorody, Ph.D., C.P.G., P.G. President President President President Universal Geoscience Consulting, Inc. Universal Geoscience Consulting, Inc.
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FACTORS AFFECTING FORENSIC ANALYSIS AND · PDF file · 2010-10-25factors affecting forensic analysis and interpretation of impacts from stray gas hydrocarbons hydrocarbons - pressure,
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FACTORS AFFECTING FORENSIC ANALYSIS AND FACTORS AFFECTING FORENSIC ANALYSIS AND INTERPRETATION OF IMPACTS FROM STRAY GAS INTERPRETATION OF IMPACTS FROM STRAY GAS
PRODUCED GAS PRODUCED GAS DENVER BASINDENVER BASIN
THERMOGENIC BIOGENIC GAS MIXTURE
INCREASINGINCREASING
THERMALTHERMAL
MATURITYMATURITY
1313
GAS RATIOS ARE UNIQUEGAS RATIOS ARE UNIQUE
INCREASINGINCREASING
THERMALTHERMAL
MATURITYMATURITYVARYINGVARYING
SOURCE SOURCE
ROCKROCK
PRODUCED GAS PRODUCED GAS DENVER BASINDENVER BASIN
1414
SOMETIMES PRESENCE OR ABSENCE SUFFICIENTSOMETIMES PRESENCE OR ABSENCE SUFFICIENTTO ELIMINATE POTENTIAL SOURCESTO ELIMINATE POTENTIAL SOURCES
20 mg/L26 mg/L
DE
LTA
D M
ET
HA
NE
pe
r m
ilD
ELTA
D M
ET
HA
NE
pe
r m
il
23 mg/L
Fruitland Well #1
Fruitland Well #2
Fruitland Well # 3
FRUITLAND GAS NOT SOURCEFRUITLAND GAS NOT SOURCE
OF GAS IN THIS WATER WELLOF GAS IN THIS WATER WELL
DELTA DELTA 1313C METHANE per milC METHANE per mil
DE
LTA
D M
ET
HA
NE
pe
r m
ilD
ELTA
D M
ET
HA
NE
pe
r m
il
WATER WELL SITE 595
WATER WELL SITE 595
WATER WELL SITE 595
CASING HEAD CASING HEAD AND AND
PRODUCTION PRODUCTION GAS GAS
COMPOSITIONCOMPOSITIONNOT NOT
PICEANCE BASINPICEANCE BASIN
NOT NOT NECESSARILY NECESSARILY
THE SAMETHE SAME
1616
SHALLOW COMMERCIAL GAS SANDS IN RULISON FIELD SHALLOW COMMERCIAL GAS SANDS IN RULISON FIELD DIFFER FROM UNDERLYING WILLIAMS FORKDIFFER FROM UNDERLYING WILLIAMS FORK
3.4
3.6
3.8
4
4.2
4.4
4.6
C2/C
3
10 15 20 25 30 35 40
W 27-3
W 46-11
W 86-29
W 13-3
W 14-24W 14-34W 15-5
W 18-27
W 19-28
PA 21-34PA 24-21
PA 32-29PA 312-21
RMV 37-33
RMV 43-28A
GV 21-35
GV 25-27
GV 75-3
LANGSTAFF 109+ BacterialMethane Trend
Maturity Trend
Source Rock Trend
2
2.5
3
3.5
Sum
C4/S
um
C5
3.4 3.6 3.8 4 4.2 4.4 4.6
W 27-3
W 46-11
W 86-29
W 13-3 W 14-24W 14-34
W 15-5
W 18-27W 19-28
PA 21-34
PA 24-21
PA 32-29
PA 312-21
RMV 37-33
RMV 43-28A
GV 21-35
GV 25-27
GV 75-3
LANGSTAFF 109
10 15 20 25 30 35 40 C1/C2
Wasatch Williams Fork
3.4 3.6 3.8 4 4.2 4.4 4.6 C2/C3
Wasatch Williams Fork
1.1
1.2
1.3
1.4
1.5
1.6
1.7
iC5/n
C5
0.9 1 1.1 1.2 1.3 1.4 iC4/nC4
W 27-3W 46-11
W 86-29
W 13-3
W 14-24W 14-34W 15-5
W 18-27
W 19-28
PA 21-34
PA 24-21
PA 32-29PA 312-21
RMV 37-33
RMV 43-28AGV 21-35
GV 25-27
GV 75-3
LANGSTAFF 109
Wasatch Williams Fork
0.89
0.9
0.91
0.92
0.93
0.94
0.95
0.96
0.97
Dry
ness (
C1/C
1+
)
0 1 2 3 4 % Non Hydrocarbons
W 27-3W 46-11
W 86-29
W 13-3
W 14-24W 14-34
W 15-5
W 18-27
W 19-28
PA 21-34
PA 24-21
PA 32-29
PA 312-21
RMV 37-33
RMV 43-28A
GV 21-35
GV 25-27
GV 75-3
LANGSTAFF 109
Wasatch Williams Fork
17
1717
CASING HEAD CASING HEAD AND AND
PRODUCTION PRODUCTION GAS GAS
STABLE STABLE ISOTOPICISOTOPIC
COMPOSITIONCOMPOSITION
PICEANCE BASINPICEANCE BASIN
COMPOSITIONCOMPOSITIONNOT NOT
NECESSARILY NECESSARILY THE SAMETHE SAME
IMPLICATIONS?IMPLICATIONS?1818
WATER/MONITOR WELL SAMPLES FOR WATER/MONITOR WELL SAMPLES FOR COLLECTING NATURAL GAS ARE OF TWO TYPESCOLLECTING NATURAL GAS ARE OF TWO TYPES
FREE GASFREE GAS
FREE GAS COLLECTEDFREE GAS COLLECTED DISSOLVED GAS DISSOLVED GAS
FREE GASFREE GAS
DISSOLVEDDISSOLVED
GASGAS
1919
ADDRESSING DISSOLVED GAS ADDRESSING DISSOLVED GAS CONCENTRATIONCONCENTRATION
METHANE SOLUBILITY IS LOWMETHANE SOLUBILITY IS LOW
Dissolved methane concentration in duplicateDissolved methane concentration in duplicatesamples varies by 9% samples varies by 9% plus or minusplus or minus 90 ug/L)90 ug/L)
Collected from water wells only Collected from water wells only
* ug/L = micrograms per liter or .001 milligrams per liter* ug/L = micrograms per liter or .001 milligrams per liter
SHORT TERM VARIABILTY ADDRESSED USINGSHORT TERM VARIABILTY ADDRESSED USINGMULTIPLE SAMPLES FROM SINGLE SITESMULTIPLE SAMPLES FROM SINGLE SITES
DISSOLVED GAS COMPOSITION DISSOLVED GAS COMPOSITION AND HENRY’S LAWAND HENRY’S LAW
�� Dissolved gas phase composition obeys Henry’s Dissolved gas phase composition obeys Henry’s Law Law under equilibrium solution & exsolutionunder equilibrium solution & exsolution•• Partial pressure controls relative solubility of source gas Partial pressure controls relative solubility of source gas
in dissolved phasein dissolved phase
•• Gas Gas exsolvedexsolved in equilibrium with a headspace will reflect in equilibrium with a headspace will reflect relative concentration of free phase source gasrelative concentration of free phase source gasrelative concentration of free phase source gasrelative concentration of free phase source gas
•• Therefore gas ratios are useful for identifying source Therefore gas ratios are useful for identifying source gases in samples with dissolved gasgases in samples with dissolved gas
�� Free gas phaseFree gas phase•• Discharge of free gas driven by pressure gradient Discharge of free gas driven by pressure gradient
maintains chemical and isotopic composition of source maintains chemical and isotopic composition of source gasgas
�� Stable isotopes not affected by solution/Stable isotopes not affected by solution/exsolutionexsolution2323
USEFUL RATIOS FOR CROSS PLOTSUSEFUL RATIOS FOR CROSS PLOTS
�� [C[C11// Σ Σ CC11+] or [C+] or [C11/C/C22]] or [or [ CC11/C/C22+C+C33 ] or ] or
[C[C22+/+/ Σ Σ CC11+]+]
•• Susceptible to biogenic methane mixingSusceptible to biogenic methane mixing
�� CC22/C/C3 3 or Cor C22// Σ Σ CC22++�� CC22/C/C3 3 or Cor C22// Σ Σ CC22++
EXAMPLE GAS RATIO IN FREE GAS PHASE VS. DISSOLVEDEXAMPLE GAS RATIO IN FREE GAS PHASE VS. DISSOLVEDPHASE: SPATIAL/TEMPORAL CHANGES PHASE: SPATIAL/TEMPORAL CHANGES