Open-hole barrier data transmissions

• An oil and gas company active in the Norwegian North Sea identified a seismic anomaly offset from a previous discovery and developed a test plan for a subsequent appraisal well
• The operator committed to perform a Drill Stem Test (DST) and as part of the test objectives, there was a requirement to continue capturing high-value subsurface pressure data beyond the DST and well abandonment in order to delineate the southern part of the original discovery
• During the appraisal operations, the well objectives changed and there was a last minute requirement to drill and test a sidetrack
• The customer wanted to ensure data from the pilot hole was still accessible, but this meant the CaTS signal had to transmit across an un-cased open-hole section; something not previously attempted before

• Our solution was to install an Advanced Reservoir Testing (ART) permanent monitoring system using two CaTS Gauges in the pilot hole on the DST tailpipe
• The gauges were programmed to ensure that full pressure build-up data was captured, and the reservoir was continuously monitored from the DST through to abandonment
• The system was commissioned and set up for receiving Pressure and Temperature data for a period of 1.5 years
• Over 20 years proprietary expertise with modelling downhole Electromagnetic signal propagation, combined with our extensive global record ensured we delivered a successful solution within a dynamic operational environment
• Expro delivered another world's first for EM data transmission to surface across an open-hole well section without casing

• The CaTS permanently installed monitoring system converted the well into a high-valve monitoring asset that allowed reservoir Pressure and Temperature data to be collected beyond well abandonment
• Wireless communications across un-case open-hole section allowed the sidetrack operations to be simplified and provide well integrity assurance by reinstating a rock-to-rock barrier
• This provided a cost effective option for well abandonment while maintaining the ability to monitor the reservoir and plug integrity
• Deploying the subsea transceiver within the cut casings below the mudline ensured compliance with NORSOK D-010 standards
• The ART system, in conjunction with our DST and well test package provided a fully integrated testing service
• The ART system delivers substantial value from interference monitoring between an abandoned pilot hole and sidetrack, without the need to drill a separate appraisal well
• It was possible to capture reservoir pressure events such as extended pressure build-ups post DST, evaluate subsurface flow barriers and monitor dynamic reservoir pressure interferences from subsequent field activities

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