characterization of fluid composition while drilling to aid well … for well... · 2021. 1. 5. ·...

Schlumberger-Private

P r e s e n t e r s : M a n e e s h P i s h a r a t , M a r i a C e c i l i a B r a v o

D o m a i n C h a m p i o n

S c h l u m b e r g e r

Characterization of Fluid Composition While Drilling to Aid Well Placement

C a s e s t u d y p r e s e n t e d a t A A P G I C E , 2 0 1 8

A u t h o r s : G a u h a r A b d r a h m a n , M a e r s k D e n m a r k ,

A l i s t a i r M a g u i r e , A l a n F e r n a n d e s , I v a n F o r n a s i e r , S c h l u m b e r g e r


Reservoir setting

• 220 km West of Esbjerg

• Total E&P Denmark A/S

• Discovered: 1991

• Year on stream: 2002

• Reservoir depth: 2,050 m

• Reserves: 50 million BBOE

• Source: Nordosfonden

2


Development Challenge

• Oil & Gas production from Tor & Ekofisk

• Since 2002:

• 11 wells drilled

• 4 P&A

• Poor well landing

• Inconsistent exposure to desired

hydrocarbons

• Decreased production

• Loss of revenue

• Well bore needs to be in targetformation and phase


A New Approach

Gas

OilDep

th (

ft.)

Fluid profile

Length (ft.)

Previous Well

Planned Well

• Maximizing reservoir contact in the correct phase

• Place high in oil leg, maintains oil production due to migrating OWC and GOC

• Advanced Surface Fluid Logging (ASFL) was the key to provide well placement

• Geochemically steering the well = World 1st


Mud Gas Data

Extraction

• Efficiency

• Reliability

• Repeatability

• Flexibility

• Maintenance

Analysis

• Detection Limit

• Components

• Principle

• Analysis time

Interpretation

• Data Analysis

• RT Transfer

• Integration

Evaluation needs

• Improve reservoir fluid evaluation along the entire well

• Accurate fluid characterization in challenging drilling

environment

Graphic from: Geosearch Logging Inc

Graphic from: Geosearch Logging Inc


Mud Gas Data Interpretation – Fluid Typing

0.00

0.05

0.10

0.15

0.00

0.05

0.10

0.15

0.15

0.10

0.05

0.00

0.15

0.10

0.05

0.00C2/SC

C3/SC

nC4/SC

Challenges• Fluid type is not only conditioned by the fluid components but also by the

reservoir conditions• Only the composition of light fluid fraction is accessible to gas measurements• The composition of the gas extracted from the mud is different from the

composition of the reservoir fluid

Triangle Method Pixler ratios Haworth ratios


From ‘gas data analysis’ to ‘Fluid Logging’

• Constant and repeatable conditions of extraction• Remove surface contamination due to gas entrained in mud• Account for variable extraction efficiency• Calibrate with known composition from field• Create continuous fluid/ fluid facies log


Creating the signature


Drilling the Well - Landing

A gradual compositional variation was observed:

• The Mol. Wt. indicates a gradual decrease

• The Aromatic/Alkanes ratio exhibits a clear drop

• The Light Heavy ratio exhibits homogeneity

• Slight increase in C1%

• Overall clear oil signature at the control point

8

Resistivity

Character

Wetness

Balance

Light/

Heavy

Mol. Wt.

Aromatic

to Alkane

XX500 X1000 X1500 X2000 X2500 X3000

C1%

C1%

100%

50%


• Clear trends in three key ratios

• Marked decrease in C1%

• Correlates with drop in well inclination

• Verified with Formation Pressure measured while drilling.

• Interpreted as differential depletion in reservoir

9

X1000

C1%C1%

100%

50%

X2000 X3000 X4000 X5000 X6000 X7000

Resistivity

Character

Wetness

Balance

Light/

Heavy

Mol. Wt.

Aromatic

to Alkane

Formation

Pressure

Drilling the Well – Steering ahead


• Marked drop in Total Gas (TG) and resistivity

• Lower volumes of soluble components

• Interpreted as an increase in Sw

• Decision made to TD well

10

C1%C1%

100%

50%X250 X500 X750 X1000 X1250 X15000

Resistivity

Character

Wetness

Balance

Light/

Heavy

Mol. Wt.

Aromatic

to Alkane

Formation

Pressure

Drilling the Well - TD


Observations

• Six fluids identified, with five similar to the original OIL PVT signature

• The heaviest oil Fluid indicates a composition with 55-56% C1

• The lightest oil Fluid indicates a composition with 79-80% C1.

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%C1 %C2 %C3 %iC4 %nC4 %iC5 %nC5

1a 82.50 7.90 3.92 1.16 2.23 1.22 1.07 17.50 9.45 1.45 2.65 20.96 0.63 -14.06

1b 77.29 8.78 4.74 1.91 3.35 2.09 1.84 22.71 6.21 1.94 1.04 23.02 -4.06 -16.87

1c 69.38 9.93 6.96 2.94 5.27 2.89 2.62 30.62 3.86 1.98 2.29 25.94 0.86 -22.16

1e 73.16 9.99 5.77 2.37 4.24 2.37 2.10 26.84 4.96 1.92 2.37 24.35 0.70 -20.00

1d 79.06 8.32 3.97 1.65 2.89 2.08 2.02 20.93 6.94 2.18 1.63 22.53 0.35 -15.18

2a 56.09 11.75 10.32 4.21 8.69 4.63 4.31 43.91 2.15 2.12 0.87 31.03 0.69 -30.76

Chs Mol Wt Aro_Alk TriangleL_HFluids Whs Bhs0% 20% 40% 60% 80% 100%


Modelled signature Measured signature

Lightest Heaviest

Observations


Observations

• Nearly all cut offs were refined

• THC Norm use with caution

• Tends to over-estimate hydrocarbon content

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RatioPrejob Model

Cut-off

Post Job Refined cut-off

Gas Undifferentiated Oil

Mol. Wt. 19 <19.5 19.5 to 21.5 >21.5

Light to Heavy 5 >5 3.5 to 5 <3.5

Aromatic to Alkane 0.5 <0.4 0.4 to 0.5 >0.5


Conclusions

• Fluid logging provides a means to obtain continuous fluid printing with calibrated

compositional data

• Delivered the primary objective & increased net reservoir by 15%

• Verified a compositional trend with Formation Pressure While Drilling

• Confirmed an increase in Sw with reduction in component volumes

• Cut offs derived from ASFL refined the petrophysical model


Thank you, Any Questions?

characterization of fluid composition while drilling to aid well … for well... · 2021. 1. 5. ·...

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