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Combined use of MWD and gyro surveyingto reduce wellbore positioning uncertainties
Simon McCulloch, Maersk Oil QatarStefan Maus, Magnetic Variation Services LLC
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Typical MOQ Well
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Typical MOQ Well
TVDSS = +/- 3200 feet
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Typical MOQ Well
TVDSS = +/- 3,200 feet
+/- 25,000 feet horizontal in reservoir
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BGGM Example
Declination: 2.24° (Magnetic North is East of True North)
Dip: 41.03°
Total field: 43,950 nT
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Accuracy of BGGM Corrected by Aeromagnetic Anomaly Survey
Declination: +/- 0.39°
Total field: +/- 130 nT
Accuracy of BGGM (1-sigma)
Declination: +/- 0.15°
Dip: +/- 0.1°
Total field: +/- 60 nT
Dip: +/- 0.2°
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40 Km
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2007 Marine Magnetic Vector Survey
Declination correction: -0.6°
Dip correction: +0.11°
Total field correction: -6nT
Declination: 2.24° 1.64°
Dip: 41.03° 41.14°
Total field: 43,950 nT 43,944 nT
BGGM Corrected by Marine Magnetic Vector Survey
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Typical Platform Spider Plot
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Typical Surface Location
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Assume vertical to seabed
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Drive conductor, or drill26” hole to 600 feetsurveying with GyroMWD
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Set 20” conductor and survey with wireline centroller gyro
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Centroller
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Drill 16” hole, surveying with GyroMWD untilfree of magnetic interference
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Drill 16” hole to TD at about 3,000 feet,surveying with magnetic MWD
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Set 13-3/8” casing and survey with wireline centroller gyro
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Centroller
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+/- 1,000 feet of comparison between magnetically clean MWD surveysand subsequent continuous gyro survey using centroller centralisationIn 13-3/8” casing
Common tie-in just before first clean MWD survey
X
X
Calculated MWD positionX Calculated gyro position
Closure angle
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Recalculate/enhance magneticMWD surveys
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Drill 8-1/2” hole surveyingwith magnetic MWD
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Recalculate/enhance magneticMWD surveys
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Drill 8-1/2” hole surveyingwith magnetic MWD
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Survey Programme of Final Definitive Survey
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Survey Programme of Final Definitive Survey
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Magnetic Measuring Stations
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MOQ Rules for the Application of an MSA Correction
Mag North
W
S
E
At the Planning Stage
• Never expect a successful MSA correction if the predominant direction of the planned horizontal hole is within +/- 30° of East/West
Once the BHA-run is complete and the raw data have been inspected
• Survey management company uses rules based on SPE/IADC 125677 Nyrnes, Torkildsen & Wilson
“Minimum Requirements for Multi-Station Analysis of MWD Magnetic Directional Surveys”
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Part 2:MWD Survey Analysis for Al Shaheen Field
Simon McCulloch and Stefan Maus
37th Meeting of the ISCWSA, Paris, 8-Mar-2013
• Declination inferred from 16” well sections
• Total Field and Dip from 12.25” & 8.5” well sections
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CHAMP satellite magnetic anomaly maps
+ + +
Total FieldDipDeclination
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Thickness of non-magnetic sediments
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Summary of data used from 30 wells
Hole section / data type BHA runs MWD surveys16” inch MWD surveys 28 182
16” Cazandra Multi-Station corrected MWD surveys
21 131
13⅜” Centroller Gyro runs Interpolated well positions, every 25 ft
12¼” MWD surveys 32 540
8½” MWD surveys 65 5408
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Well azimuth from MWD readings
Coordinate system with z-axis pointed in the well bore direction (Sperry) :
𝐺𝐺𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 = 𝐺𝐺𝑥𝑥2 + 𝐺𝐺𝑦𝑦2 + 𝐺𝐺𝑧𝑧2
𝐵𝐵𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 = 𝐵𝐵𝑥𝑥2 + 𝐵𝐵𝑦𝑦2 + 𝐵𝐵𝑧𝑧2
𝐵𝐵𝑑𝑑𝑑𝑑𝑑𝑑 = asin(𝐺𝐺𝑥𝑥𝐵𝐵𝑥𝑥 + 𝐺𝐺𝑦𝑦𝐵𝐵𝑦𝑦 + 𝐺𝐺𝑧𝑧𝐵𝐵𝑧𝑧
𝐺𝐺𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝐵𝐵𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡)
𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 𝑚𝑚𝑎𝑎𝑚𝑚𝑚𝑚𝑎𝑎𝑚𝑚𝑎 = atan𝐺𝐺𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 𝐺𝐺𝑥𝑥𝐵𝐵𝑦𝑦 − 𝐺𝐺𝑦𝑦𝐵𝐵𝑥𝑥
𝐵𝐵𝑧𝑧 𝐺𝐺𝑥𝑥2 + 𝐺𝐺𝑦𝑦2 − 𝐺𝐺𝑧𝑧 𝐺𝐺𝑥𝑥𝐵𝐵𝑥𝑥 + 𝐺𝐺𝑦𝑦𝐵𝐵𝑦𝑦
Coordinate system with x-axis pointed in well bore direction (Schlumberger):
𝐺𝐺𝑥𝑥 → 𝐺𝐺𝑧𝑧; 𝐺𝐺𝑦𝑦 → 𝐺𝐺𝑥𝑥; 𝐺𝐺𝑧𝑧 → 𝐺𝐺𝑦𝑦; 𝐵𝐵𝑥𝑥 → 𝐵𝐵𝑧𝑧; 𝐵𝐵𝑦𝑦 → 𝐵𝐵𝑥𝑥; 𝐵𝐵𝑧𝑧 → 𝐵𝐵𝑦𝑦;
MWD well azimuth = magnetic azimuth + declination – grid convergence
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Gyro-derived well inclination and azimuth
• Input: final gyro-derived well paths• Interpolated well path given at 25 ft intervals• Cubic B-splines fit to well positions continuous well path• Take measured depth (MD) of MWD survey• Compute inclination and azimuth by differencing the well path:
𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺 𝑤𝑤𝑚𝑚𝑤𝑤𝑤𝑤 𝑚𝑚𝑚𝑚𝑚𝑚𝑤𝑤𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝐺𝐺𝑚𝑚 = acos(𝜕𝜕𝜕𝜕𝜕𝜕𝜕𝜕 𝑀𝑀𝜕𝜕
𝜕𝜕𝑀𝑀𝜕𝜕)
𝐺𝐺𝐺𝐺𝐺𝐺𝐺𝐺 𝑤𝑤𝑚𝑚𝑤𝑤𝑤𝑤 𝑚𝑚𝑎𝑎𝑚𝑚𝑚𝑚𝑎𝑎𝑚𝑚𝑎 = atan(𝜕𝜕𝜕𝜕𝜕𝜕 𝑀𝑀𝜕𝜕 /𝜕𝜕𝑀𝑀𝜕𝜕𝜕𝜕𝜕𝜕𝜕𝜕 𝑀𝑀𝜕𝜕 /𝜕𝜕𝑀𝑀𝜕𝜕
)
Finally:Declination residual = Gyro well azimuth – MWD well azimuth
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16” section: Residuals plotted against measured depth
Residual = Gyro azimuth – MWD azimuth
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Declination anomaly at Al Shaheen
Method Surveys BHA runs Declination anomaly
1) Raw MWD surveys 182 28 -0.05° ± 0.11°2) Multi-station corrected azimuth
131 21 -0.05° ± 0.11°
3) MWD well path 183 28 -0.01° ± 0.10°
Method Surveys BHA runs Declination anomaly
1) Raw MWD surveys 182 28 -0.03° ± 0.11°2) Multi-station corrected azimuth
131 21 -0.03° ± 0.11°
3) MWD well path 183 28 +0.01° ± 0.10°
Residual against BGS Global Geomagnetic Model (BGGM) at well head
Residual against High Definition Geomagnetic Model (HDGM) at well head
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16”,12¼” & 8½”: Total field and dip residuals plotted against measured depth
Using reference values at well head
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Difference between geomagnetic reference field at well head and at survey location
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16”,12¼” & 8½”: Total field and dip residuals plotted against measured depth
Mean residuals are close to zero No crustal
magnetic anomaly at Al Shaheen
Using reference values at well head
Using reference values at survey
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Resulting geomagnetic reference uncertainty (1σ)
Declination Dip Total fieldError source bias random bias random bias randomMain field - 0.02° - 0.03° - 24 nTCrustal field (this study) -0.01° 0.10° -0.03° 0.05° 15 nT 10 nT
Disturbance field - 0.05° - 0.06° - 42 nTReference field at well head
- 0.02° -0.02° 0.05° 22 nT 17 nT
Total 1-sigma uncertainty (with bias folded in) 0.12° 0.11° 67 nT
For comparison:ISCWSA-2000 error model 0.39° 0.2° 130 nT
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Total uncertainty of actual MWD surveys(not just the geomagnetic reference)
Well section
MWD azimuth
Multi-stationcorrectedazimuth
MWD Dip MWD Total field
16 inch (below 2300 ft MD)
± 0.56° ± 0.43° ± 0.27° ± 170 nT
12¼ inch Unknown Unknown ± 0.14° ± 92 nT8½ inch Unknown Unknown ± 0.13° ± 82 nT
Standard deviation of the tool readings against the reference value.
Total uncertainties in the 12¼” and 8½” sections are about 50% lower than in 16” sections
azimuth uncertainty is about 0.3° for raw and 0.2° for multi-station-corrected azimuths?
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Results
• No crustal magnetic anomaly at Al Shaheen
– Supported by satellite data and MWD surveys
• Total uncertainty (1-sigma) of geomagnetic reference:
Simon McCulloch and Stefan Maus, Paris, 8-Mar-2013
Declination Dip Total field0.12° 0.11° 67 nT
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• Continuous gyro surveys run on wireline through casing with centroller centralisation from surface to +/-60° inclination represent the best current means of surveying our wells to the depth of the 13-3/8” casing shoe.
• With enough good quality gyro and magnetic survey data, the uncertainty of the local magnetic field can be reduced.
• Independently check all reference data.
Lessons Learned
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Combined use of MWD and gyro surveyingto reduce wellbore positioning uncertainties
Simon McCulloch, Maersk Oil QatarStefan Maus, Magnetic Variation Services LLC