Dave Hawker

DATALOG

Hydrocarbon Evaluation and Interpretation

Aims of the Course

• Identify the mechanisms of, and influences on, gas entering the drilling fluid

• Identify factors controlling the final gas magnitude and composition

• Total Gas measurement versus Chromatographic analysis

Aims of the Course (continued)

• Interpretation of real-time and depth-based logs

• Use and benefits of gas ratio analysis

• Further applications of hydrocarbon evaluation

ROP Chromatographic Gas Gas Ratios

Hydrocarbon Evaluation

• Recognition of hydrocarbon bearing zones– should zones be further tested– detect zones that may go undetected by wireline

• Determination of fluid type and contacts

• Evaluation of production potential

• Evaluation of formation pressure– well planning

• Essential component to well safety

Evaluation Considerations

• By what mechanisms can gas enter the drilling fluid?

• How much of the formation gas is detected at surface?

• How does surface composition compare to the actual reservoir fluid?

• What factors effect the quantity of gas detected?• How does gas analysis correlate with other

indicators?

Timetable - Day 1

• Petroleum Composition and Classification– Common hydrocarbon groups– American Petroleum Institute classification

• Detection and Measurement– Gas Traps– Total Gas Detectors

• Types and Limitations• Applications

– Gas Chromatography

Timetable - Day 1 (continued)

• Surface Gas Evaluation– Sources of gas– Changes in state from original

reservoir fluid– Gas solubility considerations

• Origins of Gas– Liberated, Produced, Recycled,

Contamination– Factors effecting their occurrence– Surface recognition and evaluation

Timetable - Day 1 (continued)

• Factors controlling surface quantity and composition

– Formation considerations– Drilling considerations– Importance of fluid movements– Drilling fluid system– Surface considerations

Timetable - Day 2

• Log Evaluation– Background gas & show evaluation– Recognition and evaluation of produced gases

• Chromatographic Analysis– Gas normalization– Gas ratio analysis

• Pixler ratios

• Wetness, Balance and Character Ratios

• Oil Indicator

Timetable - Day 2 (continued)

• Fluorescence Techniques– Conventional UV fluorescence versus

QFT™

• Case Studies and Applications

Petroleum

• Any hydrocarbon compound that appears naturally in the Earth’s crust– Solid (i.e. Bitumen, Wax)– Liquid (i.e. Crude)– Gas

• Composed of hydrogen and carbon atoms

• ‘Contaminants’ such as CO2, S, N2

Hydrocarbon Compounds

• Saturated Hydrocarbons– possessing single covalent bonds between the

carbon atoms

• Unsaturated Hydrocarbons– possessing double bonds between the carbon

atoms

Saturated Hydrocarbons

• ALKANES– short carbon chains with every bond occupied

by hydrogen atoms

• Paraffin– straight or branch chained

• Naphthene– cyclic chain

Straight Chain Paraffins or Normal Alkanes

Structure Name Abbreviation Formula

Methane C1 CH4

Ethane C2 C2H6

Propane C3 C3H8

Normal Butane nC4 C4H10

Normal Pentane nC5 C5H12

Straight Chained Paraffin

• Most common hydrocarbon, whether liquid or gas

• Termed the normal Alkanes

Cn H2n+2

Normal Alkanes

• Where n ranges from 1 to 10: -

Methane C1

Ethane C2

Propane C3

Butane nC4

Pentane nC5

Hexane C6

Heptane C7

Octane C8

Nonane C9

DecaneC10

Isomers

NormalIso- Neo-

Branch Chained Paraffin

• Isomers possessing 4 or more carbon atoms

• Given the same name as the normal alkanes along with the iso- prefix

• Detection at wellsite is restricted to iso-butane and iso-pentane

Paraffins - Branched Alkanes

Structure Name Abbreviation Formula

Iso Butane iC4 C4H10

Iso Pentane iC5 C5H12

Saturated Hydrocarbons

ALKANESshort carbon chains with every bond occupied by hydrogen atoms

Paraffinstraight or branch chained

Naphthenecyclic chain

Naphthene - Cyclic Chained Alkanes

Structure Name Formula

Cyclopropane C3H6

Cyclobutane C4H8

Cyclopentane C5H10

Naphthene

• Closed chained with hydrogen occupying every available bond

• Names from the Paraffin series are prefixed with cyclo-

• Molecularly lighter than paraffins but analyzed as if the same

• Associated with higher density crudes

Cn H2n

Unsaturated Hydrocarbons or Aromatics

• Saturated Hydrocarbons– possessing single covalent bonds between the

carbon atoms

• Unsaturated Hydrocarbons– possessing double bonds between the carbon

atoms

Unsaturated Hydrocarbons or Aromatics

Structure Name Formula

Benzene C6H6

Toluene C6H5CH3

Unsaturated Hydrocarbons or Aromatics

• Closed chained but not saturated with hydrogen

• Minor component to crude oils

• Benzene– most common aromatic– present in most crude oils

Cn H2n-6 C6 H6

API Classification

• Based on the Specific Gravity (gm/cc) and defined by the American Petroleum Institute

• Determined at 16°C and atmospheric pressure

• The larger the API rating, then the lighter the oil

5.1315.141 SGAPI

API Fluorescence Guide

Gas Condensate

High Gravity Oil

Medium Gravity Oil

Low Gravity Oil

Summary

• Petroleum fluids contain a complex mixture of hydrocarbon compounds

• Gas analysis is typically restricted to the lighter, common hydrocarbons– Saturated hydrocarbons

• Normal Alkanes and isomers (Paraffins)

• Cyclo-Alkanes (Naphthenes)

Baffle Type Trap

Mud sample in

Mud out

Gas is lifted with the rising air

Sample drawn to logging unit

Air In

Gas is released as mud cascades down baffles

Agitator Trap

mud flow

electric motor

mud in

gas released by impeller agitation

mud out

Air in

Gas/Air sample drawn to unit

Limitations of the Agitator

• Changes in mud flowrate– mud volume sampled

• gas available to be extracted vs efficiency of trap

• Extracted gas expelled with mud– mud flow pattern through the trap

• rotation speed, design, immersed depth, mud rheology

• Extraction efficiency– relative to individual gases

• molecular weight, solubility, mud type/viscosity,

Location and Positioning

• Directly over flowline entry

• Correct depth for maximum efficiency

• Away from cuttings obstruction

• Direction of exit port– downstream so not recycling degassed mud– avoiding wind fluctuations

Quantifying the Gas Measurement?

• Calibrate against gas-in-mud measurement– accounting for losses to the atmosphere– poor sample quality if mud is gas cut– frequency of mud gas sample

• Equate to formation gas volume by comparing cuttings to mud volume ratio– changes in liberated gas volume due to the

effects of flushing, influxes, washouts

EVALUATION OF RELATIVE CHANGES

Total Gas Detectors

• What information do they provide?

• How do the different types of gas detector vary in their operation and response?

• Of what value is Total gas measurement?

• What are the limitations to Total gas measurement?

Types of gas detectors

• Catalytic Combustion or “Hotwire”

• Thermal Conductivity

• Flame Ionization

• Infrared

• New technologies

Catalytic Combustion Detector

Platinum Wire

Catalyst

Alumina Bead

CC Operation

• Platinum filament combusts a tiny fraction of the gas that is carried through the combustion chamber

• The combustion increases the temperature of the filament resulting in a change of electrical resistance

• Resulting potential difference is measured and calibrated for gas concentration

CC Response to Hydrocarbons

• As molecular weight increases, combustion heat and detector response increase

• A registered increase can therefore be caused by higher concentrations or by a change in composition with a greater amount of heavier hydrocarbons

CC Response to Hydrocarbons

Response (relative to C1)

C1 1.000C2 1.478C3 1.812iC4 1.938NC4 1.710H2S 2.456

CC Response

Detector Response

Concentration in Air

C1C2C3

LEL

Catalytic Combustion

• Advantages– Industry standard for

30 years

– Simple, reliable, cheap

– Good sensitivity

– Response is proportional to heat energy of gas

• Disadvantages– Gas mixture has to be

below LEL

– Sensor can be poisoned

– Sensor deteriorates over time

– non linear measurement of EMA

Thermal Conductivity Detector

• The detector measures the cooling effect that the gas/air mixture has on a filament

• The response from the gas mixture is referenced against the response from air

• A greater positive response is given by molecularly lighter gases

Thermal Conductivity Detector

Response (relative to air)Air 1.00C1 1.25C2 0.75C3 0.58iC4 0.55NC4 0.55He 5.90CO2 0.60

ActiveReference

Sample

Thermal Conductivity Detector

• Methane/Air has a linear response from 0 to 100%

• All other hydrocarbons give a negative response in comparison to air

• CO2 and H2S have a lower cooling effect

• H2 and He, very light, give a large positive response

Thermal Conductivity

• Advantages– Cheap, reliable

– Long Life

– Range to 100% C1, linear measurement

• Disadvantages– Poor sensitivity <0.1%

– C2+ lowers reading

– Poor zero stability

– non linear measurement of EMA

– interference

Flame Ionization Detector

FID Circuit

Ground

A

Hydrogen

Ionization Cell (anode)Combustion Chamber (cathode)

+

air sample

FID Operation

• Complete combustion of gas sample– Large hydrogen flame means that heat

generated by combustion is negligible• This ensures a constant temperature and the most

linear response of all detectors

• Detects the ionization process when combustion breaks down the carbon-hydrogen bonds

Flame ionization

• Advantages– Excellent sensitivity

and range

– Stable

– Response equal to number of carbon atoms, linear measurement of EMA

• Disadvantages– Expensive

– Complicated

– Use of hydrogen

– May not be linear at higher concentrations (chamber size)

Infrared Detector• Detects the infrared absorption frequency unique

to different hydrocarbons• An infrared stream is passed through cells

containing a reference gas and the gas sample• A filter removes all but the frequency range of

hydrocarbons• The difference in emitted energy between the

two cells is calibrated in terms of hydrocarbon concentration

Infrared

Source

Path Filter

Detector

Gas Sample

Reference

Filter Frequency

C1 C2+

Filter Range

Frequency

Intensity

Infrared

• Advantages– 0-100% range is

possible

– No poisoning

• Disadvantages– Non linear output

– Interference gases

– Cost

– C1 output << C3+

New Technologies

• What is the detector output with varying hydrocarbon components?

• What is the detector output with varying amounts of hydrocarbons?

• Are there any cross sensitivities?

• Does the sensor have any degradation mechanisms?

The Value of Total Gas Measurement

• Continuous gas monitoring, instantaneous response

• Effective when zone is well known or only one fluid type will be encountered

• Assists the wellsite geologist in core point selection and formation tops

• Backup to chromatographic analysis

• Safety tool

• Stand-alone monitoring systems

Limitations

• Measurement is qualitative rather than quantitative

• Can not distinguish hydrocarbon type, therefore can’t identify fluid type

• Poor understanding of the differences between detector measurements

Total Gas Monitoring Systems

• Used independently by wellsite geologist

• Automated with lagged gas, ROP etc

• Cost effective determination of porosity

• Continual printout and data storage

• Well safety

• Insurance against wireline data not being run or of poor quality due to invasion

Geologger

Real-Time Display

What information do they provide?

• Continual Total Gas measurement

• Depth, Rate of Penetration

• Lag time, depth

• Rig operations (status, pump speed)

• Optional H2S

• LAS output

Geologger Printout

Chromatographic Analysis

• Absolute measurement of individual gases and hydrocarbon compounds– Separation occurs as sample passed through

columns containing separating medium• Different retention rates for gases of varying

chemical or physical properties

• Individual components passed to detector where they are analyzed and measured

Chromatographic Analysis

• Chromatographs can work on the principle of any of the previous detectors

• Particular gases analyzed dependent on:-

• separating medium• carrier gas • column temperature and pressure• separation time allowed

Chromatographic Analysis

• Samples have to be separated and analyzed before following sample can be taken

• Chromatographs can be limited by this sample cycle

• Short sample time allows for: -

• effective analysis with fast ROP’s• detection of fracture gas• identifying formation tops• identifying fluid contacts

The Portable Micro-Chromatograph

Silicon Injector

Capillary Column

Thermal Conductivity Detector

Sample Chromatogram

10 20 30elution time (seconds)

O2+N2

C1

CO2

C2

C3

iC4 nC4iC5 nC5

composite Column AColumn B

peak milli-voltage

area under curve

determine autozero

Advantages/Benefits of Chromatography

• Absolute measurement of all hydrocarbon components

• Determination of reservoir fluid type

• Determination of fluid contacts

TCD versus FID

• TCD variable response due to air flow and gas type is not a factor due to auto-zeroing and gas separation

• Micro-detector provides fast response ensuring linearity comparable to FID

• Both subject to non-linearity as a result of gas viscosity and entry into columns

• Both subject to amplifier and column saturation• FID’s requirement of hydrogen supply• Measurement of non-hydrocarbons with TCD• TCD lower sensitivity is 10ppm, FID to the ppb.