Post on 08-Feb-2018
Resistivity Behind Casing: Alternative
Approach for Reservoir Monitoring in Mature
North Sea Assets
Parijat Mukerji
Aberdeen
May 2012
Outline
Overview of Surveillance Logging
Why Resistivity Behind Casing ?
Measurement Physics, Challenges, Tool Specs
Examples
Choosing the appropriate measurement
-Application Envelope of Pulsed Neutron and Resistivity measurements
Measurements Sensitive to Oil, Water & Gas
Fluid density, rf (water~ 1–1.2 g/cc, oil~0.6–1g/cc, gas~0.1 – 0.3g/cc)
Hydrogen density/index (water/oil~1, gas~0.1)
Fluid compressibility (water 2-4 x psi-1, oil 5 – 100 x psi-1, gas 100 – 1300 x psi-1)
Carbon density (water 0, light oil~0.85rh, gas~0.75rh)
Fluid resistivity (water 0.01 – 100 W.m ,oil/gas~ ∞,)
Capture cross-section, Sf (water~22–120cu ,oil~22cu, gas~6cu,)
Relative dielectric constant, r (water ~ 80 ,oil~5, gas ~2 ,)
610 610 610
Well-logging techniques for Cased Hole Evaluation
Techniques depending on presence of carbon
Carbon/Oxygen logging (Pulsed Neutron Spectroscopy)
Techniques depending on water salinity
Chlorine logging (Pulsed Neutron Spectroscopy)
Capture cross-section, S (Pulsed Neutron Capture)
Resistivity
Common Problems
Reservoir performance below expectations, need to monitor but…
-Possible Invasion
-No baseline SIGMA log
-Porosity is below 15%
-Don’t have any log in some wells
Why Resistivity Through Casing ?
Need for essential formation evaluation data under any conditions
Large amounts of bypassed and undeveloped reserves exist.
It is cost effective and environmentally friendly to identify and extract by-passed reserves from existing wells.
Increasing need for optimal reservoir management to extend field life and postpone decommissioning
Measurement Physics
Low casing resistivity ~ 2 * 10-7 ohm-m
Measured/total current ratio: DI/I ~ 10-3 to 10-5
Measured voltages are in the nanoVolt range
Frequency of operation limited to around 1Hz
Good electrical contact essential
Challenges
Tool Specifications CHFR Plus
Logging Speed ~ 240 ft/hr
Electrode redundancy 3 per level
Tool OD 3-3/8"
Casing Size 41/2 – 95/8 in.
Temperature 150C [300F]
Pressure 15,000 psi
Length 48 ft [14.6 m]
Telemetry
Electronics
Insulating joint
Top current Electrode/Centralizer
Arm section
Hydraulics
Bottom current
Electrode/Centralizer
Tool Specifications Slim CHFR
Logging Speed ~ 240 ft/hr
Electrode redundancy 3 per level
Tool OD 2 1/8"
Casing Size 2 7/8 in to 7 in.
Temperature 150C [300F]
Pressure 15,000 psi
Length 43 ft [13.1m]
Nuclear
CHFR
Open Hole
Pulsed Neutron Saturation
OH Saturation
CHFR Saturation
Log
Example -
Resistivity/
Nuclear
Comparison
_________ Open Hole Resistivity__________
---------------Cased Hole Resistivity--------------
1600 BWPD to 300 BOPD after
Logging /Intervention
Initial perforated interval
flushed
Production Enhancement with New Perforation
Perforation opportunity
Identified from Cased
Hole resistivity log
Remedial Intervention in High Water Cut Well
CHFR / PLT Data
SPE 71715
Depth of Investigation In these, lower quality sands, the nuclear tool is still highly affected by near wellbore conditions. The zones are actually at original oil saturation as seen on the CHFR+.
Nuclear Resistivity
0 -o- Csg resistance -o- 100 (mW)
0 ___ Csg thickness __ 0.5 (USI) (in.)
Depth (m) Cement Map
(USI)
1 ------------- Open-hole Deep Laterolog ----------1000
1 -o---------o- CHFR (Pass 1 & Pass 2) -o------o-1000
Log Example: Poor Cement
Pulsed Neutron & Resisitivity through Casing
Not recommended except on expert advice.
Use it based on tool planner recommendation
Go ahead.
CO Sigma CHFR Formation
Pulsed Neutron & Resisitivity through Casing
CO Sigma CHFR Completion
Not recommended except on expert advice.
Use it based on tool planner recommendation
Go ahead.
Pulsed Neutron & Resisitivity through Casing
CO Sigma CHFR Borehole
Not recommended except on expert advice.
Use it based on tool planner recommendation
Go ahead.
CHFR Tool Planner - Inputs
CHFR Tool Planner - Outputs
Conclusions
The CHFR measurement is deeper than conventional saturation monitoring from nuclear tools and allows direct comparison with open hole resistivity logs.
Measurement independent of fluid in the casing.
Resistivity measurement can be combined with PLT and Pulsed neutron tools
CHFR locates bypassed oil and increases reserves with no environmental and minimal financial risk for our clients.
Resistivity Behind Casing: Alternative
Approach for Reservoir Monitoring in Mature
North Sea Assets
Parijat Mukerji
Aberdeen
May 2012
References
Ferguson R, et al 2001 SPE ATCE- “Direct Measurement of Formation Resistivity through Steel Casing solves a North Sea production question”
Starcher M, et al 2002 SPE Western Regional meeting “Next Generation Waterflood Surveillance: Behind Casing Resistivity Measurement Successfully Applied in the A3-A6 Waterflood at Elk Hills Field, Kern Country, California
Jiang L, et al 2009 SPWLA Annual Logging Symposium “Innovation to Enhance Recovery From Slim Cased Hole Resistivity Measurements in Gulf of Thailand
Zaini M 2007 SPWLA Annual Logging Symposium “Expanding the Operating Envelope of Effective Technology Improves Oil Recovery in Mature Fields of South Oman”