one step towards true along hole logging depths: proper ... · 1. wll and lwd need better along...
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One step towards True Along Hole logging
depths: proper WLL corrections
Amsterdam ICSWSA meeting
30th October 2014
Harald Bolt
Ton Loermans
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Why work on depth QC??• Depth one of the top uncertainty factors
FDP’s• Sensitivity analysis Net Present Value
typical FDP
• Direct impact fluid contacts on HC vol.– Extreme case: >>> 1 million bbl per 1 ft change in
GOC 2
Change in NPV FDP for assumed uncertainty in various parameters
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Accuracy & precision needed
• Fluid contacts
–A few feet difference has major impact
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- Not many examplesabout lateral error mishaps.
(…yet … )
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AH-depth and 3D position
• Limit to AH depth
• Surveying needed for 3D position
– AH depth (often) important input
• Plenty of problems challenges already
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Current practice• Wireline – loggers depth
–Normally (some) stretch corrections applied
• LWD logs – drillers depth
–Surface measured lengths
–No stretch corrections applies
• Hence grossly in error; errors not consistent
• WLL depths (used to be) believed as being better than drillers depth
–But LWD/drillers depth taken for lack of WL in horizontals
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heptacable
5” drillpipe
Drillpipe and logging cable
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heptacable
5” drillpipe
Drillpipe and logging cable
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The WLL challenge: get a really good (accurate) measurement even withsuch flimsy cable..!!)
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Depth problems common• Random field example
– 25 well field
– 7 wells with serious depth problems suspected
– 4 wells resurveyed confirmed significant problemsoriginal depths
• errors from -12 to +28 ft (< 10000 ft wells)
• (suspected) errors & mismatches jumping up & down
– one well, WLL only: 19, 29, 10, 21, 10, 30, 2 ft
– WLL/LWD mix: similar problems
• 25 % of wells have reason to worry, / too large depth discrepancy (Saudi Aramco 2013)
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Depth
Why worry about depth?
“Normal work”, eg stretching and squeezing core photos
of solid pieces of rock to match LWD depths
Current NS well:
•Drilled just for depth problem
earlier well
•Still not sure how to tackle
now..
!!!!!
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Depth mishaps
t r i a n g le
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Depth
Why worry about depth?
“Normal work”, eg stretching and squeezing core photos
of solid pieces of rock to match LWD depths
Current NS well:
•Drilled just for depth problem
earlier well
•Still not sure how to tackle
now..
!!!!!
10
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Cause of problems??
• Inadequate QC service companies??
– “type 1 errors” logging depths are simplywrong, so logs have to be shifted
• Lack of audit trail/documentationleading to “type 2” error
–Operator shifts logs, assuming they’re wrong, tomatch existing model
• “Quest for depth” (started mid 1990’s) focussed on improvementsQM/QC/audit trail
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QC not main problem; methods fall short
• Problems (often/mostly?) not from operational errors
–Not much difference various regions/countries
–Not much difference after QC improvement campaign
–Stretch profile more complicated than traditionally assumed for smooth vertical wells
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QC not main problem; methods fall short
• Problems (often/mostly?) not from operational errors
–Not much difference various regions/countries
–Not much difference after QC improvement campaign
–Stretch profile more complicated than traditionally assumed for smooth vertical wells
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Improve stretch corrections
• Current stretch corrections developedfor simple, smooth, vertical wells
–Two point correction OK
• Need improved corrections (for bothWLL and LWD)
–Newly development routines for (marked cable) WLL routines seem a major step forward
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Harald Bolt (ICT Europe)
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Measurehead systems
16courtesy of Schlumbergercourtesy of MPA and BenchMark© ICT Europe s.a.
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Calibrate, verify and correct
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• Calibrate the cable length• Verify cable length measurements• Environmental corrections
• Uncertainty statements• Audit trail
© ICT Europe s.a.
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Calibrated line length
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dual wheelmeasurehead
calibrated tension measurement device at,
or near, the measurehead
line tension measurement
enc. 1
enc. 2 wireline drum
sheave
sheave
cablehead tension
magnetic mark detector
actual cable magnetic mark
Magnetic marks => line length(measurehead interpolation between marks)Surface tension + CHT => interval line stretchΔ Line tension changes => Δ correction changesΔ tension inter-mark => Δ stretch increments
Requires:magnetic marked cablecalibrated tension devices(calibrated measurehead)
Note: changes in line tension and well bore friction =>changes in inter-mark distance =>environmental correction to line length
© ICT Europe s.a.
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Verification of depth
The difference between individual measurewheelencoder responses (per mark) are logged and compared.
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Use high resolution encoders (typ. 600 ppf).Inter-mark distance will depend on tension and st. coeff.
Cable IPD will be seen as a change in gain on both encoder responses.
© ICT Europe s.a.
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Measurewheel verification
Enc.2Enc.1
mag.mark sequence number
mag.mark sequence number
Run-1
Run-2
100’ mag.markdifference, ft
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RIH sequence POOH sequence
HUD
© ICT Europe s.a.
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Measurewheel problem example
RIH data
POOH data
Δ Enc.1 – Enc.2
Δ Enc.1 – Enc.2
Δ Ind.Depth – Enc.1
Δ Ind.Depth – Enc.1
Δ Enc.1 – Enc.2, ft Δ Ind.Depth – Enc.1, ft
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RIH sequence
POOH sequence
© ICT Europe s.a.
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Correction basics – elastic stretch
• Hooke’s Law
• General stretch equation
• Total stretch applicable to WL correction
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© ICT Europe s.a.
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Stretch coefficient behaviour
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As wireline design complexity increases, the complexity of the stretch coefficient increases
© ICT Europe s.a.
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HUD st.coeff - example
24© ICT Europe s.a.
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HUD st.coeff testing
25© ICT Europe s.a.
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Magnetic mark defined st.coeff
Using a marked cable and a calibrated measurehead,St.Coeff and tension determines the inter-mark distance
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This assumes that cable IPD has been worked out.
© ICT Europe s.a.
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Way-point measurement method
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Surf.Ten
CHT
Casing
Casing
© ICT Europe s.a.
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Available technologies and processes
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Calibrated Cable Length Cable calibration verification• Thermal expansion• Stretch Coefficient Calibration• Stretch Coefficient ProfilingHUD Stretch Coefficient Real Time Stretch Coefficient• Straight Line Stretch CorrectionWay-Point Depth with Correction• Way-Point Depth with Real-Time Stretch Coefficient
© ICT Europe s.a.
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Simple case correction comparisons ??
ind.depth
ind.depth, fttension, lbs Ind. – corr.depth, ft
data sequence number
Surf.Ten
CHT
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Elastic St.Corr
Log-down/-upcorrection
casing shoe
Δ = 5 ft
Δ = 3 ft
Δ = 8 ft
© ICT Europe s.a.
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Complex comparisons ??
ind.depth
ind.depth, fttension, lbs Ind. – corr.depth, ft
data sequence number
Surf.Ten
CHT
30
Elastic St.Corr
Log-down/-upcorrection
casing shoe
Δ = 14 ft
Δ = 3 ftΔ = 10 ft
© ICT Europe s.a.
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Wrap up
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TAH depth consortium (isn)Joint activity service companies, operators
– Main objectives: provide standards andrecommended practices for TAH depthdetermination WLL and LWD
– Expand and hone this new WLL correctionsmethod
• Consider “wheels only” WLL
• Further quantification uncertainties/errors needed
– Agree on methods for LWD stretch corrections
• Obvious ISCWSA collaboration potential
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Conclusions
1. WLL and LWD need better along hole depths
2. Proper corrections to get to real TAH (True Along Hole) depth for bothLWD & WLL possible
– New method shown for marked cable WLL
– Better than 2 / 10000 achievable
– TAH depth consortium can deliver all what is needed
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DIY fire truck model building kit
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Improve stretch corrections
• Current stretch corrections developed for simple, smooth, vertical wells
–Two point correction OK
• Need improved corrections (for both WLL and LWD)
–Tension/friction profile along well; then (simply) Hooke
–Various approaches made & published; some (even better?) coming
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Taken from Chia,
2006