de2.1.5a gas principlesv1-red 2
Post on 20-Dec-2015
6 Views
Preview:
DESCRIPTION
TRANSCRIPT
Gas Detection PrinciplesJan 2010
Support for test DE2.1.5
2
Gas DetectionGas Detection
Expression of Gas Values Measured at Surface
Gases most frequently measured:
Light alkanes (C1, C2, C3, iC4, nC4, iC5, nC5)
H2S
CO2
Units of Measurement:
% Gas in Air
Parts per million (ppm); 10,000ppm = 1%
Units (varies; usually 50 units = 1%)
3
Hydrocarbon Reservoir Fluid Types
Gas Detection
Black Oil: gas-oil ratio of 2000 standard cu. ft. (SCF)/ bbl or less
Volatile Oil: gas-oil ratio of 2000-3300 SCF/bbl
Retrograde Gas: gas-oil ratio of 3300 SCF/bbl or more, up to approx. 150K SCF/bbl
Wet Gas: >0.3 gallons of condensable liquids per 1000 SCF
Dry gas:<0.3 gallons of condensable liquid per 1000 SCF
Fluids recovered from zones of retrograde and wet gases are commonlycalled ‘condensates’.
A saturated reservoir contains sufficient gas to result in a ‘cap’ of free gas.
4
Saturated Hydrocarbons
Gas Detection
ParaffinsAlso known as alkanes, these are the most common types of hydrocarbon). Alkanes form straight or branched (isomer) chains of atoms with the general arrangement: Cn H(2n + 2)
Saturated hydrocarbons have single bonds between carbon atoms.
CycloparaffinsAlso known as napthenes, these form ring structures. Each component is given the name of the corresponding paraffin, with the prefix cyclo-. They have the general arrangement:
Cn H2n
6
Structure of Light Alkanes
Gas Detection
The different arrangements (and thus physical sizes) of C4-C5 alkanes of the same composition explains why we must measure each arrangement separately in chromatography.
In practice, neo pentane does not occur in amounts measurable by conventional equipment.
7
Boiling points of Alkanes
Gas Detection
C1: -161.52°C -258.73°F
C2: -88.51°C -127.49°F
C3: -42.08°C -43.75°F
iC4: -11.81°C -10.75°F
nC4: -0.51°C 31.08°F
iC5: 27.84°C 82.12°F
nC5: 36.07°C 96.82°F
neoC5: 9.5°C 49.1°F
8
Hydrocarbon (reservoir and source) data is obtained from analysis of drilled gases and mud hydrocarbon content
Gas DetectionGas Detection
Gas Extraction from Drilling Mud
Gas transport to Mud Logging Unit
Hydrocarbon Analysis Total Gas Chromatograph C1 - nC5
Data Recording & Correlation
Gas Line
Spare Gas Line
DryingAgent
Total GasDetector
Chromato-graph
CompressedAir Supply
Vent
Vent
CalibrationSystem
RecordingEquipment
Degasser
Mud LoggingUnit
Return Mud FlowFrom Well
(Auxiliary Gas Detection Equipment Not Shown)
In-lineH S Sensor2
Pump
Pump
9
Standard Colours Used for Gas Charts
Gas Detection
Total gas: Black
C1: Red
C2: Green
C3: Medium Blue
iC4: Magenta (reddish-purple)
nC4: Cyan (light blue)
iC5/nC5: Not defined, usually black
10
Total Gas vs. Chromatography
Gas Detection
Total Gas Measurement: Continuous curve of aggregate hydrocarbons C1-nC5 (plus occasional heavier HCs)
Chromatography: batch separation and individual measurement of light hydrocarbons (usually C1-nC5)
C1
Time
TG
Gas %in air
Gas %in air
Time
11
Chromatogram
Gas Detection
The arrival of the separated gases at the detector results in a signal thatdescribes a series of peaks vs. time. This chromatogram is normallyonly displayed for calibration and troubleshooting purposes. Final outputis a histogram plotted for each gas, after computer processing.
12
Gas sampling should take place as close to the well bore as possible
Gas DetectionGas Detection
13
Gas DetectionGas Detection
1. Conventional degasser with standard chromatograph (cycle >200 sec)
2. Conventional degasser with high speed chromatograph (cycle <50 sec)
3. Reserval degasser, installed near bell nipple, with Reserval analyser
Imaging Reservoir Zones
16
Flame Ionization Detector (FID)
Min. Sensitivity: 1-5 ppm
Measurement Range: 0-30% (0-100% with dilution)
Advantages:
Very low threshold of detection
High repeatability
Linear signal response
Disadvantages:
Detects alkane HC only
Requires continuous supply of H2
Increased complexity
'Collector'
IonisingFlame
Signal to flame jet
Carrier + gas
Hydrogen
Combustion air
+
-Polarising voltage
from regulated power supply
Signalground
Electrometer(signal amplifier)
Resistance
Signal out
Gas DetectionGas Detection
17
FCP / FGP and Pump Unit
Gas DetectionGas Detection
C1-C5 AnalysisChromato cycle: 240 secondsMin. Resolution 5-10 ppm
C1-C5 AnalysisChromato cycle: 42 secondsMin. Resolution 5 ppm
GFF (Geoservices Fast FID)
Standard or QGMGas Trap+
Standard Gas Detection
or
18
Reserval Gas Analyser
Reserval Advanced Gas Evaluation
C1-C5 AnalysisChromato cycle: 42 secondsMin. Resolution 1 ppmGas In-Gas Out measurement (optional)
GZG Gas Trap+
Gas DetectionGas Detection
19
Methane Equivalence
Gas Detection
FID response is very specific to the detection of alkanes.
The FID Total Hydrocarbon Detector, which is calibrated to respond in equivalent methane in air, thus provides a quantitative gas richness indicator.
• Response will be specific to petroleum hydrocarbons only.
• Response will be proportional to the carbon content.
Methane equivalence is determined by applying the following equation to the chromatographic response:
C1 + 2C2 + 3C3 + 4(iC4 + nC4) + 5(iC5 + nC5)
20
Gas Chromatography-Mass Spectrometry (GC-MS)
Min. Sensitivity: 0.1 ppm
Measurement Range: 0-100%
Measures hydrocarbon and non-hydrocarbon gases
Advantages:
Extremely low threshold of detection
‘Universal’ gas detector
C1/C2 ratio higher than 8500
Gas DetectionGas Detection
Mass Chromatograms
Mass Spectra
21
Gas Detection
FLAIR Gas Analysis (GC-MS)
Gas Chromatograph-Mass Spectrometer
C1-C8 (plus non-hydrocarbon gases)Chromato cycle: 60-90 secondsMin. Resolution 0.1 ppmGas In-Gas Out Measurement (optional)
FLEX Gas Trap+
22
Min. Sensitivity: 1 ppm
Measurement Range: 0-100ppm
Advantages:
Simplicity (solid state)
Good reliability
Disadvantages:
Highly sensitive to moisture
Requires periodic activation with H2S
Must be capped when unpowered to prevent damage
Semiconductor H2S Sensor
HH22S/COS/CO22/Methane Detection/Methane Detection
23
Infrared Absorption (IFR)
Min. Sensitivity: 100ppm
Measurement Range: 0-10%(0-100% w/reduced low-endsensistivity)
Advantages:
Simplicity (solid state)
High reliability
Disadvantages:
Lower sensitivity than FID
Only single gases can be measured
Source
SourceSpacer
AnalysisCell withW indow
DetectorFront
Housing
Thin FilmFilter
RubberR ings
DetectorAssem bly
Therm istor(Tem p.
m onitor)
HH22S/COS/CO22/Methane Detection/Methane Detection
24
Sources of Gas Recovered at Surface
Gas Detection
1. Gas liberated from drilled cylinder
2. Produced gas
3. Recycled gas
4. Contamination gas.
25
Gas DetectionGas Detection
Gas Nomenclature
Liberated Gas: Gas liberated from cuttings only
Produced gas: gas entering borehole from adjacent, undrilled strata (related to pressure imbalance)
Recycled gas: residual gas in mud, recirculated through mud system and back into borehole
Contamination gas: gas entering mud stream from source other than formation or recycling
Background gas: average or ‘baseline’ liberated gas values
Connection gas/trip gas: gas produced by swabbing effects during a pipe connection or trip
26
Factors Affecting Gas Shows
Gas Detection
Accountable: (Possibility of Correction)
• Rate of Penetration• Hole Size• Flow Rate• Degasser Efficiency• Recycled fluids
Unaccountable: (Not Possible to Correct)
• Differential Pressure ( Mud weight ) Petrophysical • Type of Mud & viscosity• Surface Losses * Saturation• Swabbing * Permeability • Surging * Porosity • Caving * GOR• Diffusion * Density of fluids• Mud Loss / Mud gain• Mud temperature at flow line.
27
Sources of Gas Shows
Gas Detection
HYDROSTATIC PRESSURE OF MUD = FORMATION PRESSUREBalanced drilling
BG DUE TO CAVING, SWELLLING ANDGAS DIFUSION FROM DIFFERENT SOURCES, SUCH AS SHALE GAS, OIL AND GAS ZONES, FRACTURES etc.
Gas diffusion from shale
Diffusion from Gas Zone Diffusion from Oil Zone
Caving and Swelling
Gas seepage from Fractures
28
Effect of Differential Pressure
Gas Detection
DIFFERENTIAL PRESSURE is the main parameter that affects the gas data.
The amount of gas recovered at the surface is only a fraction of the actual gas per unit volume in the reservoir drilled.
In addition, the proportion of gas components recovered is not the same as the actual in-situ composition.
The extracted proportion of the gas components depends largely on the differential pressure.
Higher differential pressure reduces mud gas content; in particular, the heavier components will be reduced or absent
29
Effect of Differential Pressure
Gas Detection
Variations in differential pressure will affect the gas recovered at surface.
A B C Effect of differential pressure where differential is:
A: much greater than zero
B: slightly greater than zero
C: less than zero
Gas
30
Gas DetectionGas Detection
Liberated Gas
0 20 40 60
ROCKTYPE
BOREHOLE
WALLCAKE
LAG TIME
TOTALCIRCULATION
TIME
PENETRATION RATECURVE mn/m
GAS DETECTOR RESPONSEDRILLING FLUID %
L
R
BG
BG
BG: BACKGROUND GASL: LIBERATED GASR: RECYCLED GAS
NORMAL CONDITIONS
HYDROSTATIC PRESSURE (MUD) > FORMATION PRESSURE
THE GAS RELEASED TO MUD IS THE CONTENTS OFDRILLED CYLINDER OF FORMATION (BIT-SIZED)
DE
PT
H
TIM
E
FILTRATE INVASION ZONE
0 5 10 15 20 25 30
31
Effect of ROP
Gas Detection
0 20 40 60
ROCKTYPE
BOREHOLE
LAG TIME
PENETRATION RATECURVE mn/m
GAS DETECTOR RESPONSEDRILLING FLUID %
L
BG
BGBG: BACKGROUND GASL: LIBERATED GASR: RECYCLED GAS
NORMAL CONDITIONSHYDROSTATIC PRESSURE DUE TO MUD > FORMATION PRESSURE
DECREASE IN ROP PROLONGS GAS PEAKS ON THE CHART. THE NET RESULT WILL BE TO GET LOW PEAK ON THE MASTERLOG,OFTEN OCCURS IF BIT IS WORN OUT OR DUE TO SOME OTHER REASONS SUCH AS - DECREASE IN FLOW RATE, CONTROLED DRILLING, DIFFERENT TYPE OF BIT USED ON OFFSET WELLS, ETC.
DE
PT
H
TIM
E
0 5 10 15 20 25 30
32
Detection of Fluid Contact
Gas Detection
0 20 40 60
ROCKTYPE
BOREHOLE
LAG TIME
PENETRATION RATECURVE mn/m
GAS DETECTOR RESPONSEDRILLING FLUID %
L
BG
BG
BG: BACKGROUND GASL: LIBERATED GASR: RECYCLED GAS
NORMAL CONDITIONS
HYDROSTATIC PRESSURE DUE TO MUD > FORMATION PRESSURED
EP
TH
TIM
E
0 5 10 15 20 25 30
POROUS
NON POROUS
GAS
WATER
33
Flushing of Formation
Gas Detection
HYDROSTATIC PRESSURE DUE TO MUDEXCESSIVELY HIGH( MW / SG) COMPARED
TO FORMATION PRESSURE.
INVASION OF PERMEABLE ZONES WILL STOP AS MUD CAKE IS BUILT UP.
IF VERTICAL PERMEABILITY OF ZONE IS GOOD, MUD WILL FLUSH GAS OR
FORMATION FLUIDS AWAY FROM BORE HOLE.
SOME PART OF FLUIDS MAY COME TOBORE HOLE AS BIT PENETRATES
LOWER & LOWER IN OPENED ZONE.
Excessive mud density results in little or no recovery of C4/C5 hydrocarbons, making show identification very difficult.
34
Gas DetectionGas Detection
Produced Gas
0 20 40 60
ROCKTYPE
BOREHOLE
LAG TIME
TOTALCIRCULATION
TIME
Penetration RateCurve mn/m
Gas Detector ResponseTotal Gas %
L
R
BG
BG
BG: Background GasL : Liberated GasR : Recycled Gas P : Produced Gas
Formation Pressure > Hydrostatic Pressure due to Mud.
EXTRA GAS compared to gas liberated by cylinder of formation drilled is due to PRODUCTION OF GAS FROM ADJACENT FORMATION.
DE
PT
H
TIM
E
0 5 10 15 20 25 30
P
P
P
35
Swabbing : Produced gas that enters hole because of suction. This can occur due to: 1. High viscosity of mud. 2. Balled up bit. 3. Fast rate of pulling out. 4. Collar size too large for the hole. 5. Swelling of clays 6. Insufficient cutting transport.
Surging : Injection effect – mud is pushed into the formation. This can occur due to fast rate of running in, and other aspects as above.
Before each trip we are supposed to provide a Swab and Surge report to the drilling personnel.
Gas Detection
36
Drilled Gases
Gas Detection
Gas
CG
CG
CG
CG
CG
CG
CG
CG
CG
CG
A B C
A good indicator of an increase of Pf is gas swabbed from the formation during a trip or a pipe connection.
Effect of differentialpressure on connection gas:
A. Positive, stable DP
B. Positive, decreasing DP
C. Negative DP
37
COMPARISON BETWEEN A GAS KICK AND A LARGE GAS SHOW
INCREASED FLOW ATFLOWLINE AND FOAMAT BELL NIPPLE DUETO GAS CONTENT
INCREASED FLOW ATFLOWLINE AND MUD OVERFLOWS BELL NIPPLE BEFORE INTRUDING FLUIDREACHES SURFACE
DRILLING FLUID ISDISPLACED BY INTRUDING FORMATION FLUID
GAS, OIL OR WATERFLOWS INTO BOREHOLEFROM FORMATION
GAS FROM CUTTINGSEXPANDS IN ANNULUSINCREASING TOTALOUTFLOW VOLUME
GAS - BEARINGCUTTINGS
WELL BALANCED WELL UNDERBALANCED
Gas Detection
38
Recycled Gas
Gas Detection
Amount of recycled fluids depends on:
1. Efficiency of rig degasser.
2. Mud Properties, such as Visc., Temp. etc.
3. Type of mud: WBM or OBM (synthetic).
4. Oil / diesel in mud.
Reserval can measure Gas in and Gas out. Recycled fluids can be detected.
39
0
5
10
15
20
25
30
35
40
6:00
:14
6:33
:34
7:06
:54
7:40
:14
8:13
:34
8:46
:54
9:20
:14
9:53
:34
10:2
6:54
11:0
0:14
11:3
3:34
12:0
6:54
12:4
0:14
13:1
3:34
13:4
6:54
14:2
0:14
14:5
3:34
15:2
6:54
16:0
0:14
16:3
3:34
17:0
6:54
17:4
0:14
18:1
3:34
18:4
6:54
iC5 OutiC5 In
Important gas influx
(Trip gas)
Re-injection of the
recycled gas
Detection of the recycled gas,
at the flow line
17 February 2000
Recycled Gas
Gas Detection
40
Influence of Hole Size on Gas Shows
Gas Detection
17 1/2”
Same amount of gas per unit volume
of rock.
12 1/4” But different bit size changes the Total Gas.
8 1/2” Even large gas show in 17 1/2 “ hole may be water-bearing.
6”
41
Influence of Flow Rate on Gas Shows
Gas Detection
•
Cylinder of rock mixes with small volume of mud.
Slower flow rate
Same cylinder of rock mixes with larger volume of mud.
Faster flow rate
Increase in Mud Flow Rate decreases Gas recorded.
42
Influence of Measurement Frequency
Gas Detection
Reserval and ConventionalFID running simultaneously.
Curves show the difference in data acquired .
Conventional FID is not able to keep pace with fast rate of drilling.
This results in chromatographic curve with step-like appearance.
43
Influence of Thresholdof Measurement
Gas Detection
Difference between Reserval and ordinary FID out-put. Reserval has
greater consistency and higher resolution so that heavier hydrocarbons
are better represented.
44
Influence of GasTrap Mud Level
Gas Detection
Conventional gas trap may sometimes misrepresentgas out put. Trap starvation
(decrease in mud level)as in this case shows decrease in gas level as against actual
zone shown in bottom of the figure.
45
Effect of Mud Type
Gas Detection
The TYPE OF MUD also affects the composition of the gas recorded.
Water-base mud is probably the best for gas recovery, whereas contamination of the mud with crude oil increases retention of gas in mud and thus increases recycled gas.
Recycled gas makes evaluation of the gas data very difficult.
Thank you for your attention.
top related