16/april/2007© donovan brothers inc. automated mudlogging systems sm slide 1 of 46 mudlogging...

16/April/2007 © Donovan Brothers Inc. Automated Mudlogging Systems SM Slide 1 of 46

MUDLOGGING UNCONVENTIONAL GAS

RESERVOIRS

MUDLOGGING UNCONVENTIONAL GAS

RESERVOIRS

Bill Donovan, PEDonovan Brothers IncorporatedAutomated Mudlogging Systems

Our Corporate Motto

“WE DON’T PASS GAS”“WE DON’T PASS GAS”


Mudlogging Unconventional Gas Reservoirs

• Field study results• Definitions and theory• Resource comparison• Mudlogging gas content• Factors influencing mudlogging• Calibrating the system

OVERVIEWOVERVIEW


Common form of volumetric gas in place for shale and coal

G = gas in place (MCF)A = drainage area (acres)H = thickness (feet)

ρb = bulk density (gm/cc)GC = gas content (scf/ton)


Field Study ResultsField Study Results

GCHA3597.1G b




bHA3597.1GGC

Back calculated gas content is based on cumulative production and/or estimated ultimate recovery (EUR)G is cumulative production or EURA is the spacing unit

H and ρb are from logs



Field Study ResultsField Study Results55 wells with Mudlog GC (green)




55 wells with Mudlog GC (green)Cumulative Production GC (blue)



Field Study ResultsField Study Results55 wells with Mudlog GC (green)Cumulative Production GC (blue)Estimated Ultimate Recovery GC (red)



Field Study ResultsField Study Results55 wells with Mudlog GC (green)Cumulative Production GC (blue)Estimated Ultimate Recovery GC (red)Isotherm Estimated GC (purple)



• Define mudlogging

• Define mudlogging gas measurements Percent Equivalent Methane in Air (% EMA) and “Units EMA”

• Explain why mudlogging is effective

• Compare resources for different reservoirs

Definitions and TheoryDefinitions and Theory



EQUIVALENT METHANE IN AIR (% EMA) is a measure of methane in air at the measurement point (the mudlogging unit) expressed as a percent of methane in the air sample or expressed differently as10,000 parts per million methane by volume

Calibrated and measured at the mudlogging unit, the whole system is not calibrated

Although related to mudlogging gas content, % EMA is not a measure of gas in the formation

Other hydrocarbon gases are presented as methaneTypically 100 “Units EMA” equals 1% EMA



Definitions and TheoryDefinitions and TheoryMudlogging Unconventional Gas Reservoirs

MUDLOGGING IS EFFECTIVE BECAUSE:•Gas is measured at the surface under STP•Gas is insoluble in water and drilling mud•Gas expands as it travels to the surface•Mudlogging is independent of theories and models


MUDLOGGING IS EFFECTIVE BECAUSE:•Gas is measured at the surface under STP•Gas is insoluble in water and drilling mud•Gas expands as it travels to the surface•Mudlogging is independent of theories and models





MUDLOGGING IS EFFECTIVE BECAUSE:•Gas is measured at the surface at STP•Gas is insoluble in water and drilling mud•Gas expands as it travels to the surface•Mudlogging is independent of theories and models




The next five slide present the amount of gas liberated and brought to the surface for coal, shale, oil and gas reservoirs.

The red and blue colored bars to the left show gas (red) and water (blue) values relative to the reservoirs.

All slides have the same format and vertical scalesAgain the conclusion reached is that both

conventional and unconventional hydrocarbon reservoirs liberate gas in quantities significantly higher than reservoirs containing water

Resource ComparisonResource Comparison



The requirements to calculate gas volume liberated/bulk volume drilled, gas content and reservoir bulk volume mudlog gas are:

• Data typically gathered while mudlogging

• Calibrated calcium carbide lags to determine gas volumes liberated

• Simple calculations using a spreadsheet and LAS files

Mudlogging Gas Content MethodologyMudlogging Gas Content Methodology



• A measured amount of Calcium Carbide reacts with water to make determinable amount of acetylene gas: CaC2 + H20 = C2H2 +CaO

• Before mudlogging a calibration using both acetylene and methane establishes a relationship between the gases for the gas sensors in the mudlogging unit.

• Before and after the zone of interest is drilled a known amount of Calcium Carbide (acetylene) is put in the drill string during connections and pumped to the surface. The peak gas value is recorded.

• Using this data, a gas show in units EMA can be converted to SCF of gas liberated while drilling.




• If the hole volume is known, SCF/formation bulk volume (ft3) can be calculated along with BCF/section or MCF/acre-foot .

• If the formation density is known, SCF/T can be calculated.

• If Bg, the gas expansion factor is known reservoir gas volume along with Bvg or reservoir gas porosity can be calculated.




• 0.5 cup of calcium carbide yields 1.268 SCF acetylene

• 125 “units” of acetylene reads 250 units EMA in the mudlogging unit

• 0.5 cup of calcium carbide in a connection before the zone yields 200 “units” of acetylene

• Calculate a conversion factor from the above data and Avogadro's Law

• Conversion factor0.01268 SCF CH4 /1 UNIT EMA





Calculate a conversion factor from data on the last slide and Avogadro's Law

Conversion factor =

Conversion factor =0.01268 SCF CH4 /1 UNIT EMA

22

422

22

2

2

22

HCSCF1

CHSCF1

EMAUnits125

HCUnits250

HCUnits200

CaCCUPS5.0

CaCCUPS5.0

HCSCF268.1



• Gas reading in the zone 570 UNITS EMA/minute

• Calculate gas liberated per minute in the zone by multiplying gas reading by the conversion factor

• 570 UNITS EMA /minute X 0.01268 SCF/UNIT EMA=7.23 SCF/Minute




• Penetration rate in the zone is 0.5 minutes/foot

• Hole diameter is 8.5 inches• Calculate the hole bulk volume

(BV) drilled per minute• Hole Volume/Minute =

0.78813 BV Cubic Feet/Minute




• Divide the gas liberated per minute by the hole volume drilled per minute

• 7.23(SCF/Minute) /0.78813(BV CF/Minute) =9.17 SCF/BV CF

• Conversion factors can be used to calculate BCF/Section foot or MCF/Acre foot




• Zone density is 1.4 gms/cc• Convert hole BV CF to Tons by

using density • Gas content 210 SCF/Ton• Zone depth 1,000’, Bg = 36.4• Convert SCF to Reservoir CF

by using Bg• Bulk Volume Mudlog Gas

0.25 CF/BV or 25%




The factors which influence mudlogging can be grouped into two general categories:

• Deterministic factors

(hole size, drilling rate, etc.)

• Indeterminate factors

(flushing, background gas, surface losses, gas trap performance)

Carbide calibration accounts for all factors

Factors Influencing MudloggingFactors Influencing Mudlogging



Deterministic factors affecting mudlog gas are:

• Gas in the formation

• Hole size

• Drilling rate

• Mud pump rate

• Gas expansion




If all other factors are equal, doubling the gas in the formation doubles the gas show




If all other factors are equal, doubling the hole diameter, quadruples the gas show




If all other factors are equal, doubling the drilling rate, doubles the gas show




If all other factors are equal, doubling mud pump rate, decreased by one half the gas show




If all other factors are equal, doubling the depth of the formation doubles the gas show in conventional reservoirs



Indeterminate factors are:

• Recycled gas in the drilling mud (minor)

• Contamination of mix water or mud chemicals (seldom)

• Flushing or flowing in the formation being drilled (minor)

• Flushing or flowing in the formations above the formation being drilled (minor)





More indeterminate factors are:

• Cuttings not fully releasing gas (minor)

• Surface losses (major)

• Gas trap design (major)

• Temperature (major)

• Wind (seldom)

• Miscalibrated sensors (seldom)




Gas trap efficiency and measurement stability is the largest cause of mudlogging error. See the SPE, Williams and Ewing article.

GAS IN THE MUDGA

S A

T T

HE

MU

DL

OG

GIN

G

UN

ITFactors Influencing MudloggingFactors Influencing Mudlogging



“Improved Methods for Samplings Gas and Drill Cuttings”, Williams and Ewing,SPE FE, June 1989




GRIGas Measurements DuringMud Logging Operations




EFFECT OF TEMPERATURE ON THE SOLUBILITY OF GAS IN WATER

0

2

4

6

8

10

0 50 100 150 200 250

TEMPERATURE (DEGREE F)

SO

LU

BIL

ITY

AT

TE

MP

ER

AT

UR

E/S

OL

UB

ILIT

Y

AT

180 D

EG

RE

ES

FA

HR

EN

HE

IT

CH4 @ T/ CH4 @ 180 F

C2H2 @ T/ C2H2 @ 180 F




GRIGas Measurements DuringMud Logging Operations



Notice all the potential errors:• 100 units of gas in the mud could read as high as 200

units or as low as 3 units due to gas trap design• Gas losses as much as 40% due to loss in the flow line• Gas losses as much as 50% due to wind• A six fold change in methane solubility in water from

40ºF to 180ºFAll of these losses can be normalized or compensated for

by the use of calibrated carbide lagging. The next slide shows that acetylene behaves like methane over a wide range of conditions. If carbide lag results are consistent, it indicates good quality mudlogging





SOLUBILITY OF GAS IN WATER

0

10

20

30

40

50

60

70

80

0 50 100 150 200 250

TEMPERATURE (DEGREE F)

SO

LU

BIL

ITY

RA

TIO

(C

2H

2/C

H4

)

RATIO

Calibrating the System


Mudlogging is an effective evaluation toolIf you have questions or comments contact

meBill Donovan

(303) 794-7470

[email protected] www.mudlogger.com


mailto:[email protected]

16/april/2007© donovan brothers inc. automated mudlogging systems sm slide 1 of 46 mudlogging...

Documents

measure of gas

mudlogging unit

independent of theories

drilling mudgas

percent of methane

measure of methane

cumulative production

units ema equals