Risk-Based Abandonment-Prioritization Strategy for Inactive Subsea Wells
- Adam Wilson (JPT Special Publications Editor)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- January 2017
- Document Type
- Journal Paper
- 69 - 70
- 2016. Society of Petroleum Engineers
- 1 in the last 30 days
- 79 since 2007
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This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 181020, “Risk-Based Abandonment-Prioritization Strategy for Inactive Subsea Wells,” by Abimbola Oladipo, Maersk Oil North Sea UK, and Adrian Houlbrook, DNV GL, prepared for the 2016 SPE Intelligent Energy International Conference and Exhibition, Aberdeen, 6–8 September. The paper has not been peer reviewed.
This paper describes how an exploration-and-production company successfully developed and applied a qualitative risk-based abandonment-prioritization strategy for an inventory of inactive subsea wells. The exercise entailed a qualitative-assessment methodology using 25 well-integrity-related criteria. An aggregate of weighted scores was subsequently applied to the company’s corporate risk-assessment matrix on the basis of the escalation potential in the event of a loss of containment. The results clearly highlighted the wells with the highest risks.
The inactive subsea wells relevant to the exercise are distributed across the central North Sea in water depths ranging from 244 to 474 ft. These normal-pressure/normal-temperature subsea wells are all located in the mature UK Central North Sea offshore basin and were completed in relatively benign reservoirs with comparatively low corrosion susceptibility.
Each inactive subsea well evaluated had functioned earlier in its life as an oil producer (with gas lift capability), water injector, or aquifer well. The majority of these subsea wells were shut in and disconnected from their flowlines and hydraulic-control and data-acquisition systems. However, the wells’ physical isolation from the flowlines and great distance from the host installation meant that they presented negligible safety risks to personnel onboard the installations.
Because degradation is not driven solely by age, and having recognized that each well behaves differently, the methodology (Fig. 1) required each well to be assessed on the basis of evidential information presented and in accordance with how closely the well followed the corporate standard ideal integrity model of its well type. A specific set of scoring guidelines was developed and reflected corporate risk-management protocols to achieve a consistent, fair, and accurate risk ranking. These guidelines were based on a number of factors, including but not limited to the technical integrity of key elements, evidential documentation, field service history, incident records, and well-integrity maintenance records.
An initial classification was applied on the basis of the available design life of key surface equipment (in this case, subsea horizontal spool trees and wellheads) and well functionality, thus enabling each well to be classified broadly into one of three preliminary-risk-assessment categories: high, medium, or low.
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