4 gas ratios
TRANSCRIPT
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Dave Hawker
DATALOG
Hydrocarbon Evaluation and Interpretation
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Gas Normalization
• Porosity, saturation, permeability• hole depth and diameter• penetration rate• bit type• flowrate• differential pressure• mud type and rheology• fluid movements• pressure and temperature change• trap efficiency and losses
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Gas Normalization
• Normalize the ‘geometric’ factors so that they can be eliminated as variables
• Cannot normalize Total Gas values since they are qualitative, not an absolute measurement
• Chromatographic components are totaled to give a Total Chromatograph Gas value
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Gas Normalization
• Can only normalize the gas measurement that we have; cannot account for: -
• losses of gas to atmosphere
• gas retained by cuttings
• phase and solubility changes
• fluid movements in terms of flushing and incursions
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Normalization Formula
dc
ba
N
100
22000
N = normalized gas (%)
a = pump output (m3/min)
b = ROP (min/m)
c = hole diameter (mm)
d = total chromatograph gas (%)
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Comparing Adjacent Shows 0 min/m 15 0.1 Gas 100
10%3 min/m
1 min/m 20%
10 min/m BG 1%
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Possible Causes of Difference
• Lower porosity and bulk volume of gas
• Lower gas saturation
• Reduced permeability
• Increased permeability resulting in flushing
• Different gas composition
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Porosity
Permeability (increase or decrease)
Composition
Saturation
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3 min/m 10%
1 min/m 20%
12 1/4” hole
Flow 2m3/min
8 1/2” hole
1.4 m3/min
Shale Background 1%, 10min/m
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Rule of Thumb vs Normalization
• Sand 1 ~ 3 times ‘better’ than shale
• Sand 2 ~ 2 times ‘better’ than shale
• Sand 1 normalized 24.8% / BG 0.84%
• Sand 2 normalized 18.0% / BG 1.22%
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Shows in different wells/hole sectionsFlowrate m3/min Normalized Gas %
ROP min/m Total Chromatograph %
0 312 ¼ “
8 ½ “
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Ratio Analysis
• Comparison of chromatographic values for individual hydrocarbon components
• reservoir fluid type
• gas/oil/water contacts
• oil gravity
• production potential; wet zones/permeability
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Pixler Ratio Plot
• Comparison of the methane content to each other alkane
• Only the value of the gas show above the background level is used– eliminates variables since they affect both– only information concerning the relative
production potential is used
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Pixler Ratio Plot Information
• Reservoir Fluid
• Oil Gravity and Gas Wetness
• Production Potential
• Permeability
• Presence of Formation Water
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Ratio Plot
NON-PRODUCTIVE GAS
PRODUCTIVE GAS
PRODUCTIVE OIL
NON-PRODUCTIVE RESIDUAL OIL
C1/C2 C1/C3 C1/C4 C1/C5
1
10
1000
100
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Ratio Plot Zones
• Determined from the comparison of gas ratio data to production and test results
• Can be used as a guide or reference
• Regional calibration will improve the effectiveness of the ratio plot
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C1/C2 Ratio
<2 very low gravity, high density and viscosity, non-productive, residual oil
2 - 4 low gravity oil, 10-15 API
4 - 8 medium gravity oil, 15-35 API
8 - 15 high gravity oil, API >35
10 - 20 gas condensate
15 - 65 gas
> 65 light gas, principally methane, non-productive
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Slope of the Curve
• A fully positive slope confirms productive hydrocarbons
• A negative slope indicates a water bearing zone• Gradient similar to the zone lines indicates good
permeability• The steeper the slope, the tighter the formation• if C1/C2 is low in the oil section, with C1/C4 high
in the gas section, zone is probably non-productive
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Evaluation of Oil Bearing Zones
GAS
OIL
NON-PRODUCTIVE
C1/C2 C1/C3 C1/C4 C1/C5
1
10
100
1000
NON-PRODUCTIVE
Medium-High API
Good Permeability
himed
lo
API
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Evaluation of Oil Bearing Zones
GAS
OIL
NON-PRODUCTIVE
C1/C2 C1/C3 C1/C4 C1/C5
1
10
100
1000
NON-PRODUCTIVE
Medium-High API
Tight
himed
lo
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Evaluation of Oil Bearing Zones
GAS
OIL
NON-PRODUCTIVE
C1/C2 C1/C3 C1/C4 C1/C5
1
10
100
1000
NON-PRODUCTIVE
Medium-Low API
Fair-Good Permeability
himed
lo
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Evaluation of Oil Bearing Zones
GAS
OIL
NON-PRODUCTIVE
C1/C2 C1/C3 C1/C4 C1/C5
1
10
100
1000
NON-PRODUCTIVE
Medium-Low API
Water Bearing
himed
lo
Permeability?
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Evaluation of Oil Bearing Zones
GAS
OIL
NON-PRODUCTIVE
C1/C2 C1/C3 C1/C4 C1/C5
1
10
100
1000
NON-PRODUCTIVE
Very low API
non-productive?
Water Bearinghi
med
lo
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Evaluation of Gas Bearing Zones
GAS
OIL
NON-PRODUCTIVE
C1/C2 C1/C3 C1/C4 C1/C5
1
10
100
1000
NON-PRODUCTIVE
1 3
2
4
1. Methane
Tight, non-productive
2. Productive Gas
Good Permeability
3. Productive Gas
Tight
4. Light Gas
Permeability?
Water Bearing
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Condensates ?
• Indicated by C1/C2 between 10 and 20
• 10 - 15 also indicates high gravity oil
• 15 - 20 also indicates gas
20
15
10
Hi API Oil
Gas
Condensate
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Condensates ?
• Gas, typically yields a more definitive C1/C2 ratio
• Complication with light oils having high Gas Oil Ratio
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Prediction of Gas Condensate
GAS
OIL
NON-PRODUCTIVE
C1/C2 C1/C3 C1/C4 C1/C5
1
10
100
1000
NON-PRODUCTIVEPlots follow a similar gradient to the upper gas limit
C1/C2 ratio suggests a higher proportion of heavier hydrocarbons
Wet Gas or
Condensate ?
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Prediction of Gas Condensate
GAS
OIL
NON-PRODUCTIVE
C1/C2 C1/C3 C1/C4 C1/C5
1
10
100
1000
NON-PRODUCTIVE
Light Oil, reduced permeability
Light Oil with high GOR
Condensate
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Correlation with Fluorescence
C1/C2 Ratio API Gravity Fluid Type NaturalColour
Colour ofFluorescence
2 – 4 10 – 15 Low Gravity Oil Dark brown toblack
Orange to brown
4 – 8 15 – 35 Medium GravityOil
Light to mediumbrown
Cream to yellowgreen, gold
8 – 15 > 35 High Gravity Oil Clear White to bluishwhite to blue
10 – 20 ~ 50 Gas Condensate ‘Gasoline’ Violet if visible
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Ratio Plot Summary
C1/C2 C1/C3 C1/C4 C1/C5
1
10
100
1000
himed
lo
API
Dry gas
Wet Gas
Non-productive gas Geopressure methane
Heavy, viscous, non-productive Residual oil, tars, waxes
Gas Condensate
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Drawbacks to the Gas Ratio Plot
• Difficult to determine condensate reservoirs
• Optimally, requires regional re-calibration
• Limited number of plots for each potential zone
• Plots are offline, so that information is apart from the mud log
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Wetness, Balance and Character Ratios
• Calculated real-time for immediate evaluation and recognition of reservoir changes and contacts
• Plotted on a depth-based log for comparison with other mud logging and wireline data for effective reservoir evaluation
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Wetness Ratio
• Increasing trend as proportion of heavy gas increases, i.e. as gas or oil density increases
• Determination of gas wetness and oil density
10054321
5432
CCCCC
CCCCWh
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Wetness Ratio
<0.5 non-productive dry gas; non-associated or geopressured methane
0.5 - 17.5 gas, increasing in wetness
17.5 - 40 oil, increasing in density (decreasing gravity)
>40 non-productive oil, very low gravity, residual
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Wetness Ratio
1 10 100
NON-PRODUCTIVE, RESIDUALOIL
POTENTIAL OIL PRODUCTION
POTENTIALGAS PRODUCTION
NON-PRODUCTIVEDRY GAS
Increasing density or wetness
Increasing density
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Balance Ratio
• Compares light to heavy gases
• Responds inversely to Wh as fluid density increases
• Used in conjunction with Wh for interpretation
543
21
CCC
CCBh
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Interpretation of Wetness and Balance
Balance Ratio Wetness Ratio Reservoir Fluid and Production Potential
> 100 Very light, dry gasTypically non-associated and non-productive such asthe occurrence of geopressured methane
< 100 < 0.5 Possible production of light, dry gas
Wh < Bh < 100 0.5 – 17.5 Productive gas, increasing in wetness as the curvesconverge
< Wh 0.5 – 17.5 Productive, very wet gas or condensate or high gravityoil with high GOR
< Wh 17.5 – 40 Productive oil with decreasing gravity as the curvesdiverge
<< Wh 17.5 – 40 Lower production potential of low gravity, low gassaturation oil
> 40 non productive, very low gravity, residual oil
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Wetness and Balance Curves0.1 0.5 1.0 10 17.5 40 100
NON-PRODUCTIVE GAS
POSSIBLE PRODUCTIVE GAS
PRODUCTIVE GAS
GAS, OIL or CONDENSATE
PRODUCTIVE OIL
RESIDUAL OIL
DRY
WET
HI GRAV
LO GRAV
Wh
Bh
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Character Ratio
• Ch < 0.5– confirms productive gas phase, either Wet
Gas or Condensate
• Ch > 0.5– indicates productive liquid phase, so that gas
is associated with oil
3
54
C
CCCh
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Combining all Gas Ratios
1 10 17.5 40 1000 3
Dry Gas
IncreasingWetness
Gas or Condensate
High Gravity Oil with High GOR
DecreasingGravity
Residual Oil
Wetness RatioBalance Ratio
Character Ratio
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Summary
• Ratio curves provide very effective trend analysis on a real-time and mud log basis
• Accurate determination of reservoir fluid changes and contacts
• Immediate evaluation as reservoir is being drilled
• Definitive values require, optimally, regional calibration with test or production results
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Oil Indicator
• Compares Methane to Heavy Gases
• Ranges 0.01 to 1, increasing with gas and oil density
1543
CCCCO
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Inverse Oil Indicator
• Inverse of the oil indicator
• Ranges 1 to 100, increasing as the fluid density decreases
5431
CCCCI
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Evaluation of the Oil Indicator Ratios
Oil Indicator Evaluation Inverse Oil Indicator
0.01 - 0.07 dry gas, gas charged water 100 - 14.3
0.07 - 0.10 condensate, light oil with 14.3 - 10.0high GOR
0.10 - 0.40 oil 10.0 - 2.5
0.40 - 1.0 residual oil 2.5 - 1
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Using the Inverse Oil Indicator
1 10 100
Dry Gas
Condensate orLight Oil/Hi GOR
Oil
Residual Oil
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Ratio Summary
• Correctly interpreted, chromatographic gas ratios provide an excellent means of reservoir evaluation and determination of fluid type, contacts, permeability and the presence of water
• Regional calibration against known data will improve their accuracy
• Ratio comparisons and trend evaluation should be used rather than direct quantitative analysis
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Ratio Limitations
• Heavier oils that do not possess the lighter range of hydrocarbons
• Oils with low gas saturation
• Large proportion of produced gas may lead to false proportions
• If mud type, rheology, surface system lead to suspect gas measurements
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Conventional Fluorescence
• Colour under ultra-violet light being an indication of the density of the petroleum fluid
• The intensity of the fluorescence being an indication of the presence of water
• Solvent cut as an indication of density and mobility
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Fluorescence Colour
High API gravity oil
Medium API gravity oil
Low API gravity oil
Very low gravity, typically low intensity
Condensate
10
15
35
45
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Solvent Cut
• Solvent takes the fluid into solution and leaches it out of the cutting
• Speed and nature of the ‘cut’ reflects fluid density, viscosity, solubility and permeability
• The better the permeability, the faster the cut
• The lower the viscosity, the faster the cut
• Uniform blooming indicates good permeability and mobility
• Streaming cut indicates reduced permeability and/or high viscosity
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Limitations to UV Fluorescence
• Subjective colour descriptions
• Presence of contaminants
• Much of the fluorescence emissions fall in the ultra-violet range of the spectrum– any fluorescence visible is only a fraction of the
total emission– Some emissions may go completely undetected
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Quantitative Fluorescence Technique™
• Measurement of the fluorescence intensity which is proportional to the quantity of oil
• Old, stored cuttings can be re-evaluated with this technique
• How representative are the cuttings?
• How much fluid has been retained by the cuttings?
• Fluorescence intensity is not linear across the range of oil gravities
• Cannot be used in gas wells
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Quantitative Fluorescence Technique™
• Elimination of subjective descriptions
• QFT™ measures the oil content as given by the fluorescence intensity so that increases can represent an increased amount or a change in composition
• Total Scanning Fluorescence (TSF™) measures the entire excitation wavelengths of a given crude, with the peak defining the dominant composition
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QFT™ vs Gas/Fluorescence
Reservoir Top
Reservoir Base
Fluoresence
QFT Total Gas
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