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, r f (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 6 (water 2-4 x 10 psi -1, oil 5 100 x 10 6 psi -1, gas 100 1300 x 6 10 psi -1 ) Carbon density (water 0, light oil~0.85r h, gas~0.75r h ) Fluid resistivity (water 0.01 100 W.m,oil/gas~,) Capture cross-section, S f (water~22 120cu,oil~22cu, gas~6cu,) Relative dielectric constant, r (water ~ 80,oil~5, gas ~2,)
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 Challenges 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
Telemetry Top current Electrode/Centralizer Insulating joint Electronics Arm section Hydraulics Tool Specifications CHFR Plus Logging Speed ~ 240 ft/hr Electrode redundancy 3 per level Tool OD 3-3/8" Casing Size 4 1 /2 9 5 /8 in. Temperature 150 C [300 F] Pressure 15,000 psi Length 48 ft [14.6 m] 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 150 C [300 F] Pressure 15,000 psi Length 43 ft [13.1m] Bottom current Electrode/Centralizer
Log Example - Resistivity/ Nuclear Comparison Pulsed Neutron Saturation OH Saturation CHFR Saturation Open Hole CHFR Nuclear
Production Enhancement with New Perforation ---------------Cased Hole Resistivity-------------- Open Hole Resistivity Perforation opportunity Identified from Cased Hole resistivity log Initial perforated interval flushed 1600 BWPD to 300 BOPD after Logging /Intervention
Remedial Intervention in High Water Cut Well
CHFR / PLT Data SPE 71715
Depth of Investigation Nuclear Resistivity 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+.
Log Example: Poor Cement 0 -o- Csg resistance -o- 100 (mw) 0 Csg thickness 0.5 (USI) (in.) Depth (m) 1 ------------- Open-hole Deep Laterolog ----------1000 1 -o---------o- CHFR (Pass 1 & Pass 2) -o------o-1000 Cement Map (USI)
Pulsed Neutron & Resisitivity through Casing Formation CO Sigma CHFR Not recommended except on expert advice. Use it based on tool planner recommendation Go ahead.
Pulsed Neutron & Resisitivity through Casing Completion CO Sigma CHFR Not recommended except on expert advice. Use it based on tool planner recommendation Go ahead.
Pulsed Neutron & Resisitivity through Casing Borehole CO Sigma CHFR 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