evaluacion gases cromatografia
DESCRIPTION
Relaciones de GasesCromatografia PetroleoTRANSCRIPT
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Dave Hawker
DATALOG
Hydrocarbon Evaluation and Interpretation
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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
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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
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ROP Chromatographic Gas Gas Ratios
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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
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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?
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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
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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
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Timetable - Day 1 (continued)
• Factors controlling surface quantity and composition
– Formation considerations– Drilling considerations– Importance of fluid movements– Drilling fluid system– Surface considerations
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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
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Timetable - Day 2 (continued)
• Fluorescence Techniques– Conventional UV fluorescence versus
QFT™
• Case Studies and Applications
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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
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Hydrocarbon Compounds
• Saturated Hydrocarbons– possessing single covalent bonds between the
carbon atoms
• Unsaturated Hydrocarbons– possessing double bonds between the carbon
atoms
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Saturated Hydrocarbons
• ALKANES– short carbon chains with every bond occupied
by hydrogen atoms
• Paraffin– straight or branch chained
• Naphthene– cyclic chain
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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
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Straight Chained Paraffin
• Most common hydrocarbon, whether liquid or gas
• Termed the normal Alkanes
Cn H2n+2
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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
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Isomers
NormalIso- Neo-
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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
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Paraffins - Branched Alkanes
Structure Name Abbreviation Formula
Iso Butane iC4 C4H10
Iso Pentane iC5 C5H12
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Saturated Hydrocarbons
ALKANESshort carbon chains with every bond occupied by hydrogen atoms
Paraffinstraight or branch chained
Naphthenecyclic chain
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Naphthene - Cyclic Chained Alkanes
Structure Name Formula
Cyclopropane C3H6
Cyclobutane C4H8
Cyclopentane C5H10
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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
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Unsaturated Hydrocarbons or Aromatics
• Saturated Hydrocarbons– possessing single covalent bonds between the
carbon atoms
• Unsaturated Hydrocarbons– possessing double bonds between the carbon
atoms
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Unsaturated Hydrocarbons or Aromatics
Structure Name Formula
Benzene C6H6
Toluene C6H5CH3
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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
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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
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API Fluorescence Guide
Gas Condensate
High Gravity Oil
Medium Gravity Oil
Low Gravity Oil
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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)
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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
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Agitator Trap
mud flow
electric motor
mud in
gas released by impeller agitation
mud out
Air in
Gas/Air sample drawn to unit
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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,
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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
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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
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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?
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Types of gas detectors
• Catalytic Combustion or “Hotwire”
• Thermal Conductivity
• Flame Ionization
• Infrared
• New technologies
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Catalytic Combustion Detector
Platinum Wire
Catalyst
Alumina Bead
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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
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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
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CC Response to Hydrocarbons
Response (relative to C1)
C1 1.000C2 1.478C3 1.812iC4 1.938NC4 1.710H2S 2.456
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CC Response
Detector Response
Concentration in Air
C1C2C3
LEL
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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
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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
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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
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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
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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
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Flame Ionization Detector
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FID Circuit
Ground
A
Hydrogen
Ionization Cell (anode)Combustion Chamber (cathode)
+
air sample
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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
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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)
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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
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Infrared
Source
Path Filter
Detector
Gas Sample
Reference
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Filter Frequency
C1 C2+
Filter Range
Frequency
Intensity
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Infrared
• Advantages– 0-100% range is
possible
– No poisoning
• Disadvantages– Non linear output
– Interference gases
– Cost
– C1 output << C3+
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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?
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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
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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
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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
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Geologger
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Real-Time Display
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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
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Geologger Printout
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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
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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
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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
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The Portable Micro-Chromatograph
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Silicon Injector
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Capillary Column
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Thermal Conductivity Detector
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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
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Advantages/Benefits of Chromatography
• Absolute measurement of all hydrocarbon components
• Determination of reservoir fluid type
• Determination of fluid contacts
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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.
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