Dave Hawker

DATALOG

Hydrocarbon Evaluation and Interpretation

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

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

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

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 (%)

Comparing Adjacent Shows 0 min/m 15 0.1 Gas 100

10%3 min/m

1 min/m 20%

10 min/m BG 1%

Possible Causes of Difference

• Lower porosity and bulk volume of gas

• Lower gas saturation

• Reduced permeability

• Increased permeability resulting in flushing

• Different gas composition

Porosity

Permeability (increase or decrease)

Composition

Saturation

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

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%

Shows in different wells/hole sectionsFlowrate m3/min Normalized Gas %

ROP min/m Total Chromatograph %

0 312 ¼ “

8 ½ “

Ratio Analysis

• Comparison of chromatographic values for individual hydrocarbon components

• reservoir fluid type

• gas/oil/water contacts

• oil gravity

• production potential; wet zones/permeability

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

Pixler Ratio Plot Information

• Reservoir Fluid

• Oil Gravity and Gas Wetness

• Production Potential

• Permeability

• Presence of Formation Water

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

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

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

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

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

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

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

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?

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

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

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

Condensates ?

• Gas, typically yields a more definitive C1/C2 ratio

• Complication with light oils having high Gas Oil Ratio

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 ?

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

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

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

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

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

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

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

Wetness Ratio

1 10 100

NON-PRODUCTIVE, RESIDUALOIL

POTENTIAL OIL PRODUCTION

POTENTIALGAS PRODUCTION

NON-PRODUCTIVEDRY GAS

Increasing density or wetness

Increasing density

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

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

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

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

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

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

Oil Indicator

• Compares Methane to Heavy Gases

• Ranges 0.01 to 1, increasing with gas and oil density

1543

CCCCO

Inverse Oil Indicator

• Inverse of the oil indicator

• Ranges 1 to 100, increasing as the fluid density decreases

5431

CCCCI

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

Using the Inverse Oil Indicator

1 10 100

Dry Gas

Condensate orLight Oil/Hi GOR

Oil

Residual Oil

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

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

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

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

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

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

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

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

QFT™ vs Gas/Fluorescence

Reservoir Top

Reservoir Base

Fluoresence

QFT Total Gas