Abstract
One of the most common challenges faced by well operators worldwide is extending the lifetime of their aging platform wells. The initial well construction, operational loading and time-dependent deterioration of a well through field life are all key factors that need to be understood to establish the remaining capacity of a well. However, often these factors are not fully understood and consequently costly decisions to repair or abandon wells can be made unnecessarily, or in some cases critical wells or operations on wells are not identified, risking structural collapse of a well. To address these issues, this paper describes the factors that influence the integrity of the well, and presents advances in the approaches to understand and evaluate the condition of a well and hence better evaluate remaining capacity. Methods, Procedures, Process: Typically, corrosion of the casings is taken as the key parameter to establish a well's remaining capacity. However, as demonstrated in this paper through an analytical evaluation, the axial loading in the well is another key parameter that needs to be understood. A range of factors affect the well axial loads based on well construction and deterioration is considered, including:
Weight of casing hung off wellhead during installation
Level of axial support provided by casing shoe
Cement levels
Changes to well configuration
Changes to well service (Producer to Injector)
Changes to operating temperatures and pressures through field life
Corrosion and other deterioration of the conductor and casings
This information can, however, be difficult to obtain due to incomplete or inaccurate construction records or difficulties in taking direct measurements or inspecting a well. This paper demonstrates the influence of each of these variables on the capacity of the well, how the uncertainty in these variables affects this assessment, and consequently the overall uncertainties in establishing the remaining capacity of a well. Results, Observations, Conclusions: Having established the limitations and uncertainties of an analytical evaluation and the need to establish well axial loads, the paper also proposes a method to characterise the axial loads in a well, including a proposed technique for in-field measurement as an input to establishing a well's on going fitness for service alongside corrosion measurements. Novel/Additive Information: Overall, the paper presents an improved approach to establishing the suitability of a well for life extension based on an improved understanding of the influence of well loads, with widespread application to aging platforms in the North Sea and globally.
