1

Ministry of Energy, Mines and Petroleum Resources

DETERMINING GAS CONTENT FROM MUD GAS LOGS

Examples From Northeastern British Columbia

DETERMINING GAS CONTENT FROM MUD GAS LOGS

Examples From Northeastern British Columbia

Warren Walsh, PGeoMinistry of Energy, Minesand Petroleum Resources

Warren Walsh, PGeoMinistry of Energy, Minesand Petroleum Resources

Bill Donovan, PEDonovan Brothers IncorporatedAutomated Mudlogging Systems

Bill Donovan, PEDonovan Brothers IncorporatedAutomated Mudlogging Systems

2

Purpose� Calibrate mud log to indicate total gas

content� cc/g (scf/tonne)

� Continuous �log based� gas content data

� Compare to desorption work from core/cuttings

� Regional evaluations

� Calibrate mud log to indicate total gas content

� cc/g (scf/tonne)

� Continuous �log based� gas content data

� Compare to desorption work from core/cuttings

� Regional evaluations

3

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)

� 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

4

� 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

� 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

Mud Logging � Gas Detection

5

Gas Log Measurement

� Calibrate the gas log� while drilling � used measured calcium carbide

lags� or

� post drilling � estimate expected gas released from reservoir zones

� Calibrate the gas log� while drilling � used measured calcium carbide

lags� or

� post drilling � estimate expected gas released from reservoir zones

� Gas log measurement � direct linear relationship with

volume of gas released

� Gas log measurement � direct linear relationship with

volume of gas released

6

Assumptions

� Factors affecting mudlog gas:� Gas content of formation

� doubling the gas in the formation doubles the gas show� Hole size

� doubling the hole diameter, quadruples the gas show� Drilling rate

� doubling the drilling rate, doubles the gas show� Mud pump rate

� doubling mud pump rate, decreased by one half the gas show

� Gas expansion� doubling the depth of the formation doubles the

gas show in conventional reservoirs

� Factors affecting mudlog gas:� Gas content of formation

� doubling the gas in the formation doubles the gas show� Hole size

� doubling the hole diameter, quadruples the gas show� Drilling rate

� doubling the drilling rate, doubles the gas show� Mud pump rate

� doubling mud pump rate, decreased by one half the gas show

� Gas expansion� doubling the depth of the formation doubles the

gas show in conventional reservoirs

7

Assumptions

� When volume of rock is drilled:� Gas contained within porosity is

released� Adsorbed gas is released?

� When volume of rock is drilled:� Gas contained within porosity is

released� Adsorbed gas is released?

� Gas log measurement � direct linear relationship with volume of

gas released

� gas content = Vg/(Vr * r)

� Gas log measurement � direct linear relationship with volume of

gas released

� gas content = Vg/(Vr * r)

LL

AA

8

Assumptions

� Volume of gas contained within porosity (free gas)

� Adsorbed gas � held on organic material

� Volume of gas contained within porosity (free gas)

� Adsorbed gas � held on organic material

Volume of gas contained within porosity (free gas)

Volume of gas contained within porosity (free gas)

Conventional Sandstone

Conventional Sandstone

Shale Shale

9

Adsorbed Gas

Pressure (depth)

Gas V

olume

Isotherm

0.0

10.0

20.0

30.0

40.0

50.0

60.0

>1.01.0 - 0.420.42 - 0.250.25 - 0.15<0.15Diameter (mm)

wt %

y = 5.9901x1.3446

R2 = 0.8997

0.001

0.01

0.1

1

10

100

0.01 0.1 1 10diameter size mm

time t

o 80%

desor

bed i

n hou

rs ..

0.5 mm 135 minutes

0.075 mm 10 minutes

� Gas is released with a decrease in pressure

� How much is �lost�during trip up the hole

� Gas is released with a decrease in pressure

� How much is �lost�during trip up the hole

10

How should this compare with canister desorption

� Free gas� Free gas Lost gasLost gas Desorbed gasDesorbed gas RemainingRemaining

Desorption lost gas calculations

Desorption lost gas calculations Desorption Desorption

Estimated by , Sg, P

Estimated by , Sg, P

Mud log gas showMud log gas show

ResidualcalculationsResidualcalculations

11

* =

Calibration Method

Mud GasMud Gas ROPROP Normalized Mud Normalized Mud Gas (NMG)Gas (NMG)Gamma Gamma

RayRay

12

Calibration Method

PorosityPorosity ResistivityResistivity Normalized Mud Normalized Mud Gas (NMG)Gas (NMG)

Reservoir Zone

NMG

Est. V

gy = mx

Gamma Gamma RayRay

13

Calibration Method

Gamma Gamma RayRay

Normalized Mud Normalized Mud Gas (NMG)Gas (NMG)

gas content =Vg/(Vr * r)

Vg = NMG/m

Gas Content Vg/mGas Content Vg/m

14

� 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

� 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

Case Study � Cretaceous

15

� Organic-rich basal (ORB) layer (Wilrich/Moosebarshale)

� Average thickness � 29m � Adsorbed gas capacities

range between 0.03 and 1.55 cc/g

� Organic-rich basal (ORB) layer (Wilrich/Moosebarshale)

� Average thickness � 29m � Adsorbed gas capacities

range between 0.03 and 1.55 cc/g

Chalmers, G., UBC PhD Thesis

Case Study � Cretaceous

16

� 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

� 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

Case Study � Cretaceous 00/C-29-F/94-G-8/0

17

0100020003000400050006000700080009000

10000400600

8001000

12001400

Depth

Gas (units)

1 10 100

ROP (min/m)

� Core and cuttings collected for desorption

� Bluesky/Gethingsandstone at base of section for calibration

� Errors in digitizing/recording of mud gas log??

� Core and cuttings collected for desorption

� Bluesky/Gethingsandstone at base of section for calibration

� Errors in digitizing/recording of mud gas log??

y = 46223x

02000

40006000

800010000

1200014000

16000

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35NMG

Est. V

g

PC Beg 53-F/94-G-1

18

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

� 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

19

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

� 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

20

PC Jedney 29-F/94-G-8

� Two different reservoir zones used to calibrate log

� Harmon 1 � 2 cc/g� Wilrich 1 � 3.5

cc/g

� Two different reservoir zones used to calibrate log

� Harmon 1 � 2 cc/g� Wilrich 1 � 3.5

cc/g

y = 142793x

y = 120603x

0

5000

10000

15000

20000

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14NMG

Est. V

g

Halfway Zone Calibration

Cretaceous zone

21

Conclusions � Next Steps

� Regional evaluation of shale gas potential

� Regional evaluation of shale gas potential

Warning � this is still qualitative �

Warning � this is still qualitative �

22

Oil and Gas Division Ministry of Energy Mines and Petroleum Resources

� �Shale Gas in Northeastern British Columbia: Industry Activity Report�

Information Circular 2007-02� �Shale Gas Potential: Core and Cuttings

Analysis, Northeast British Columbia�� PG Openfile 2007-01� �Regional Shale Gas Potential of the Triassic

Montney and Doig formations�� PG Openfile 2006-02.

� �Gas Shale Potential of Devonian Strata, Northeastern British Columbia�

PG Special Paper 2005-01

� �Shale Gas in Northeastern British Columbia: Industry Activity Report�

Information Circular 2007-02� �Shale Gas Potential: Core and Cuttings

Analysis, Northeast British Columbia�� PG Openfile 2007-01� �Regional Shale Gas Potential of the Triassic

Montney and Doig formations�� PG Openfile 2006-02.

� �Gas Shale Potential of Devonian Strata, Northeastern British Columbia�

PG Special Paper 2005-01

www.gov.bc.ca/emprwww.gov.bc.ca/empr