Turning a Negative into a Positive: Shale Annular Barrier Identification for Plug and Abandonment
- David Lavery (Halliburton) | Venkat Jambunathan (Halliburton) | Gulnara M. Shafikova (Vår Energi AS)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- SPWLA 60th Annual Logging Symposium, 15-19 June, The Woodlands, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2019. held jointly by the Society of Petrophysicists and Well Log Analysts (SPWLA) and the submitting authors
- 7 in the last 30 days
- 200 since 2007
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Although shale formations can be problematic while drilling a well, those same shales have mobile characteristics that can make them extremely valuable as barriers during plug and abandonment (P&A) operations. Under certain circumstances, the mobility of shale formations can displace against the casing and create impermeable annular barriers. The impermeable nature of the displaced shale formation enables it to act as an acceptable annular barrier where the cement annular barrier is not of acceptable quality.
Particularly relevant to P&A operations, the ability to efficiently identify suitable shale annular barriers during logging can negate the need for any expensive and timeconsuming remedial cement work, yet ensure well integrity for P&A.
A comprehensive road map is described to identify shale annular barriers using acoustic and ultrasonic logging tools. Using available openhole data, the expected shalebarrier impedance-log response was predicted, providing additional confidence in the results. The simultaneous ultrasonic casing-inspection data are integrated into the shale-barrier assessment to measure the casing ovality, a feature of formation displacement compared to a cement annular barrier. A robust pass-or-fail criterion was established before logging operations.
Multi-variable threshold processing (MVTP) was used to automatically compare the logged result to the established criteria for an acceptable formation barrier and enabled the operator to determine the way forward before the logging tools were even at the surface.
Case studies are presented from multiple wells as part of a P&A campaign to highlight the success of shale-barrier identification using logging tools ostensibly designed for cement-evaluation logging. The integrity of the shale barriers was subsequently confirmed using pressure testing in accordance with the relevant regulations.
The Jotun field was discovered in 1994 and began production in 1999. It is located on the Utsira High, between the Balder and Heimdal fields, approximately 200 km west of Stavanger, Norway. The field is developed with two installations: Jotun A and Jotun B. The wellhead platform Jotun B transfers the resources to the production vessel Jotun A.
|File Size||3 MB||Number of Pages||12|