Determining Gas Content From Mud Gas Logs

Ministry of Energy, Mines and
Petroleum Resources
DETERMINING GAS CONTENT FROM
MUD GAS LOGS
Examples From Northeastern British Columbia
Warren Walsh, PGeo
PGeo
Ministry
Ministry of
of Energy,
Energy, Mines
Mines
and
and Petroleum
Petroleum Resources
Resources
Bill Donovan, PE
PE
Donovan
Donovan Brothers
Brothers Incorporated
Incorporated
Automated
Mudlogging
Automated Mudlogging Systems
Systems
1
Purpose
• Calibrate mud log to indicate total gas
content
•• cc/g
cc/g (scf/tonne)
(scf/tonne)
• Continuous “log based” gas content data
• Compare to desorption work from
core/cuttings
• Regional evaluations
2
Mud Logging – Gas Detection
• Mud logging records lots of information
about rocks/fluid/drilling activities
• Gas detection (gas log)
• record of natural gas in circulated drilling fluid
(mud)
• Reported as total gas (gas units) and Rate
Of Penetration (ROP) (T/L)
ROP is T/L is inverse velocity
3
Mud Logging – Gas Detection
• Direct measure of hydrocarbons
• Measured at surface (STP)
• Gas is insoluble in water and drilling mud
• Note: measured not by volume or depth
drilled but relative to time
4
Gas Log Measurement
• Gas log measurement
• direct linear relationship with
volume of gas released
• Calibrate the gas log
• while drilling – used measured calcium carbide
lags
• or
• post drilling – estimate expected gas released
from reservoir zones
5
Assumptions
• Factors affecting mudlog gas:
• Gas content of formation
•• doubling
doubling the
the gas
gas in
in the
the formation
formation doubles
doubles the
the gas
gas show
show
• Hole size
•• doubling
doubling the
the hole
hole diameter,
diameter, quadruples
quadruples the
the gas
gas show
show
• Drilling rate
•• doubling
doubling the
the drilling
drilling rate,
rate, doubles
doubles the
the gas
gas show
show
• Mud pump rate
•• doubling
doubling mud
mud pump
pump rate,
rate, decreased
decreased by
by one
one half
half the
the gas
gas
show
show
• Gas expansion
•• doubling
doubling the
the depth
depth of
of the
the formation
formation doubles
doubles the
the
gas
show
in
conventional
reservoirs
gas show in conventional reservoirs
6
Assumptions
• Gas log measurement
•• direct
direct linear
linear relationship
relationship with
with volume
volume of
of
gas
gas released
released
• gas content = Vgg/(Vrr *
rr)
L • When volume of rock is drilled:
A
• Gas contained within porosity is
released
• Adsorbed gas is released?
7
Assumptions
Volume
Volume of
of gas
gas contained
contained
within
porosity
within porosity (free
(free gas)
gas)
Conventional
Sandstone
•• Volume
Volume of
of gas
gas contained
contained
within
porosity
within porosity (free
(free gas)
gas)
•• Adsorbed
Adsorbed gas
gas –– held
held on
on
organic
material
organic material
Shale
8
Adsorbed Gas
• Gas is released
with a decrease in
pressure
• How much is “lost”
during trip up the
hole
Isotherm
Gas Volume
60.0
50.0
30.0
20.0
Pressure (depth)
10.0
<0.15
0.25 - 0.15 0.42 - 0.25
1.0 - 0.42
Diameter (mm)
>1.0
0.0
100
10
1
0.1
0.01
0.001
time to 80% desorbed in hours ..
wt %
40.0
0.01
y = 5.9901x 1.3446
R2 = 0.8997
0.5 mm 135 minutes
0.075 mm 10 minutes
diameter size mm
0.1
1
10
9
How should this compare with
canister desorption
•• Free
Free gas
gas
Lost
Lost gas
gas
Estimated
Estimated by
by
,, Sg,
Sg, P
P
Desorption
Desorption lost
lost gas
gas
calculations
calculations
Desorbed
Desorbed gas
gas
Desorption
Desorption
Remaining
Remaining
Residual
Residual
calculations
calculations
Mud
Mud log
log gas
gas show
show
10
Calibration Method
Gamma
Ray
Mud Gas
*
Normalized Mud
Gas (NMG)
ROP
=
11
Calibration Method
Normalized Mud
Gas (NMG)
Porosity Resistivity
Reservoir
Zone
Est. Vg
Gamma
Ray
y = mx
NMG
12
Calibration Method
Gamma
Ray
Normalized Mud
Gas (NMG)
Gas Content Vg/m
Vg = NMG/m
gas content =
Vg/(Vr * r)
13
Case Study – Cretaceous
• Regionally extensive
• (10 M Ha – 38k sq miles)
• Public domain data
including mud gas logs
• Limited exploration of
this target compared
with other shale units in
NE BC
14
Case Study – Cretaceous
• Organic-rich basal (ORB)
layer (Wilrich/Moosebar
shale)
• Average thickness – 29m
• Adsorbed gas capacities
range between 0.03 and
1.55 cc/g
Chalmers, G., UBC PhD Thesis
15
00/C-29-F/94-G-8/0
Case Study – Cretaceous
• Petro-Canada experimental
scheme targeting the lower
Cretaceous – 2002 - 2005
• 3 wells drilled total targeting
the (2 with public domain
gas detection logs)
• Harmon shale core
desorption indicates gas
content up to 1.2 cc/g
16
Gas (units)
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
400
PC Beg 53-F/94-G-1
600
• Core and cuttings
collected for
desorption
• Bluesky/Gething
sandstone at base of
section for calibration
y = 46223x
• Errors in
digitizing/recording of
mud gas log??
800
Depth
1000
16000
14000
1200
Est. Vg
12000
10000
8000
6000
4000
2000
ROP (min/m)
100
10
1
1400
0
0
0.05
0.1
0.15
NMG
0.2
0.25
0.3
0.35
17
PC Beg 53-F/94-G-1
• Errors in
digitizing/recording of
mud gas log still leave
some question to
accuracy
• Harmon 0.75 – 1.8 cc/g
• Wilrich 0.6 – 1.4 cc/g
18
PC Bubbles 94-F/94-G-8
• Well drilled specifically to
collect shale data
• Did not penetrated
underlying conventional
zones
• Log was calibrated
relative to the desorption
data
• Harmon 0.5 – 1.4 cc/g
• Wilrich 0.8 – 2.2 cc/g
19
PC Jedney 29-F/94-G-8
• Two different
reservoir zones
used to calibrate
log
20000
Halfw ay Z one Calibration
Cretaceous zone
15000
Est. Vg
y = 142793x
10000
y = 120603x
5000
0
0
0.02
0.04
0.06
NMG
0.08
0.1
0.12
0.14
• Harmon 1 – 2 cc/g
• Wilrich 1 – 3.5
cc/g
20
Conclusions – Next Steps
• Regional evaluation of
shale gas potential
Warning – this is still
qualitative –
21
Oil and Gas Division
Ministry of Energy Mines and Petroleum Resources
••
••
••
••
••
“Shale
“Shale Gas
Gas in
in Northeastern
Northeastern British
British
Columbia:
Industry
Columbia: Industry Activity
Activity Report”
Report”
Information
Information Circular
Circular 2007-02
2007-02
“Shale
“Shale Gas
Gas Potential:
Potential: Core
Core and
and Cuttings
Cuttings
Analysis,
Analysis, Northeast
Northeast British
British Columbia”
Columbia”
PG
PG Openfile
Openfile 2007-01
2007-01
“Regional
“Regional Shale
Shale Gas
Gas Potential
Potential of
of the
the Triassic
Triassic
Montney
Montney and
and Doig
Doig formations”
formations”
••
PG
PG Openfile
Openfile 2006-02.
2006-02.
“Gas
“Gas Shale
Shale Potential
Potential of
of Devonian
Devonian Strata,
Strata,
Northeastern
Northeastern British
British Columbia”
Columbia”
PG
PG Special
Special Paper
Paper 2005-01
2005-01
www.gov.bc.ca/empr
22