evaluacion gases cromatografia
DESCRIPTION
Relaciones de GasesCromatografia PetroleoTRANSCRIPT
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.