In Field Referencing Angus Jamieson Tech 21

1
In Field Referencing Angus Jamieson Tech 21

• MWD and the Earths Magnetic Field

2
MWD Relies on the Earths Magnetic Field
3
A Powerful Force but subject to three Variations
1. Secular Variation Long slow changes in the
earths magnetic core. Typical Size Fractions
of a deg/year Cured By BGGM model 2.
Diurnal Variation Rapid daily variations caused
by solar wind and earth rotation. Typical Size
0.2 degs (Randomized) Cured By
Interpolated In Field Referencing (IIFR) 3.
Crustal Variation Permanent local effects caused
by deep, magnetic basement rock Typical Size 1
degree Cured By In Field Referencing
(described later) IFR
4
Secular Variation

• Observatories around the world provide data to
  the BGS in Edinburgh from which they make a
  prediction model called BGGM
• British Global Geomagnetic Model

5
Diurnal Variation

• The earth is constantly bombarded by ionised
  material from the solar wind creating a ripple
  effect in the magnetic field.
• The earth is also rotating creating a sine wave
  effect in the magnetic field.
• By observing distant land stations in real time,
  the diurnal effects can be interpolated locally.
• This is known as Interpolated In-Field
  Referencing or IIFR. (not to be confused with IFR)

6
Crustal Variation

• Caused by the magnetic effect of deep basement
  rock.
• Cannot be corrected with Global models
• Can be a degree or more in declination
• Must be measured in the field

7
Measuring the Crustal Variation

• Until 1998, this was usually done by air.
• The aircraft would measure the strength of the
  magnetic field over a wide area.
• The field strength survey was then Inverted to
  estimate the compass effects locally.
• This estimate was found to be accurate and
  reliable where it could be tested but a direct
  measurement was difficult at sea.

8
Direct Measurement of the Earths Magnetic Vector

• In 1998, the BGS, Shell and Tech 21 researched
  and developed a technique to measure the magnetic
  vector directly at sea or on land.
• A wide area survey was no longer necessary and
  the local drilling footprint or even a single
  well route could be surveyed at surface.

9
Measuring the Earths Magnetic Vector

• Requirements
• A high accuracy attitude sensor
• Very precise tri-axial magnetometers
• Detailed measurements of diurnal variation during
  the survey

10
Calibrating the Equipment on a Land Frame
11
At sea, a Non-Magnetic Vessel carries the
measuring frame
12
Surveying is usually done in 10km x 10km grids at
2km spacing
13
(No Transcript)
14
Results in graphical and
software form
15
How the Accuracy Improves

• The contribution to Uncertainty made by the
  Compass Reference Error is reduced from approx 1
  degree to 0.25 degs.
• Other sources contribute another 0.4 degs
• Total MWD Accuracy is about twice as good

16
Benefits

• Improved MWD reduces or eliminates the need for
  gyro surveys
• Cheaper Survey Program
• Less Survey Rig Time
• Reduced Risk

17
Typical Error Propagation
18
Typical Error Propagation
Blue Raw MWD Only 97 metres Brown Gyro to 13
3/8 then Raw MWD 82 metres Green Gyro to 13 3/8
plus Gyro to 9 5/8 then MWD 47 metres Red Gyro
to 13 3/8 then IFR MWD 44 metres
19
Benefits

• Larger Target Sizing reduces Steering Requirement
• Faster Drilling Progress
• Less Tortuosity
• Improved Hole Cleaning

20
Benefits

• Reduced Well Path Uncertainty During Drilling
• Reduced Collision Risk
• Fewer Corrections
• Better well placement at target

21
Reduced Uncertainty During Drilling
22
Benefits Contd

• Improved Well Log Positioning
• More Accurate Geological Modelling
• Historical Well Data can be corrected
• Improved Reserves Estimation

23
Two wells approaching the same formation create a
Ghost Fault Interpretation
24
Some Further Benefits

• Improved Survey QC
• Satisfies survey verification requirements
  without running additional tools.
• Less unnecessary rejection of good MWD
• Easier Recognition of Faulty MWD
• Reliable Magnetic Interference Calibration

25
Conclusions and Way Forward

• Over 50 Successful Marine Magnetic Surveys
  carried out so far in the North Sea
• Campaign in 2004 for Brunei Shell Petroleum
  (combined land and marine)
• Campaign in 2005 in West Africa (marine only)
• Clear economic benefits have been achieved for
  all users of IFR
• Method Recommended for other fields at SPE
  Conference Europec 2002