Integrity Assessment of Well Barriers Threatened by Increasing Casing-Hanger Loads
- Eivind H. Okstad (SINTEF) | Sigbjorn Sangesland (Norwegian University of Science and Technology)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- June 2009
- Document Type
- Journal Paper
- 286 - 292
- 2009. Society of Petroleum Engineers
- 1.6 Drilling Operations, 3 Production and Well Operations, 1.14 Casing and Cementing, 7.2.3 Decision-making Processes, 3.1.6 Gas Lift, 1.14.1 Casing Design, 2 Well Completion
- well integrity, influence diagram, casing-hanger loads, well-barrier schematics, barrier diagram
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Degradations or interruptions of the original well-barrier elements might occur at offshore wells after some time in operation. Experience from the Norwegian Continental Shelf (NCS) has shown that these problems are not always treated as thoroughly as expected by the parties involved. This paper presents an approach for an efficient visualization and description of interrupted well barriers, basically to increase the well-barrier control and management. By mapping the history of operational demands and load picture of the well in combination with the status of well barriers, a consistent basis for evaluations is obtained. The main intention is thus to realize the real well problem and its underlying causes in a controlled and systematic manner. Then, the responsible parties involved can take action more accurately according to the type of failure that has been revealed.
Interrupted barrier elements are related to well integrity and are critical from the point of view of safety, but also concerning production regularity and costs. Failure in the well-barrier functions caused by degradations or interruptions of barrier elements needs immediate attention from the responsible bodies. During drilling and well activities, there are always to be at least two independent and tested well barriers after the surface casing is in place, according to the activities regulations of the Norwegian Petroleum Safety Authority (PSA) (2006).
Experience from PSA (Vignes et al. 2006) has shown that barrier failures occur both in newly drilled wells and in wells that have been in operation for some time. Well-integrity failures may be latent in the early constructing phase, or imposed through later maintenance tasks. Shifting between well operational phases can also initiate abnormal load situations causing well-integrity failures to occur. Many of these "unexpected" loads are not necessarily taken into account in the design phase. An investigation carried out by the PSA on the NCS showed that 14% of 309 checked wells currently in operation had problems with, or deviations related to, the well integrity (Vignes et al. 2006). Experience has also shown that integrity problems are not always treated as systematically and thoroughly as expected by the well operators.
The main objective of this paper is to present a visualization method for the purpose of evaluating well-integrity problems that communicates facts about integrity problems to the responsible bodies. Intended users of the approach are operators, contractors, government/safety authorities, researchers, and consultants who have interest in carrying out assessments of well-integrity matters. As one possible application, the options regarding the future operation of wells may be clarified by the operator, with new preconditions and operational limitations.
A brief introduction to the technical-problem area is given from a system perspective. Important casing-hanger loads are described including those operational and geological factors that make the casing-hanger load reach abnormal values. Then, a description of the three-step visualization method follows. Implications of the method are discussed, and some remarks regarding applications are given. Finally, some conclusions are outlined.
|File Size||329 KB||Number of Pages||7|
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