The ever-increasing scope of environments into which today's oilfield activities have moved require many more extremely complex operations to be used. Because of the added complexity and the increasing costs of operations, especially in subsea environments, considerable upfront planning time to develop the ‘optimal’ completion design must be spent. Operators realize that once a completion strategy is set and acted upon, any deviation from the original plan can result in significant cost increases. It has been the immediate and future costs resulting from initial planning errors that have driven operators to seek more efficient and less complex completion methods that will provide greater assurance that goals will be met.
In developing well completions, the design focus usually is performed in steps. First, the lower-completion equipment and sand-control service tools that ensure zonal stimulation, fluid-loss control, and zonal isolation are considered. Then, the design moves to the upper completion design that includes all equipment that transports hydrocarbons to surface. A significant upper-completion issue has been the difficulties experienced in spacing out and landing the hanger and tubing systems. Spacing-out operations are a significant part of land, shelf, and subsea completions; however, this paper will focus on the subsea arena.
The growing need for more efficient systems for spacing out in deepwater arenas has resulted in the development of several new system configurations and completion components that will be discussed in this paper. Of primary interest is the long-space-out telescoping joint, which helps to resolve many of the issues experienced when landing the hanger and tubing systems.
Completion costs are a critical factor when determining the financial returns that can be expected from an oil and gas investment. This factor becomes even more paramount in situations where operating costs are anticipated to be high, such as in subsea environments, where reserves are marginal, and/or where the environments are such that completion problems are more likely to occur. Safety-first, efficient practices are the primary concerns for most completion methods, and one critical area in completion practices is the spacing-out or landing of tubing hangers. This process involves installation of the production string and associated components of a particular length within a certain measured-depth window. In land, inland water, and on shelf applications, the production tree and hanger (the production tubing support mechanism) is on surface, which allows for an easier process for installing the aforementioned equipment (Smith et al., 2009) (Clarkson et al., 2008)
This paper discusses the history of space-out methods and will present a long-space-out telescoping joint specifically designed to resolve subsea space-out issues. This telescoping joint is designed to collapse in response to a non-shearing compressive load, after landing a production seal assembly into a sealbore packer below. After the joint collapses, the production tubing can be lowered to land the subsea tubing hanger into the subsea tubing-head spool.
The hardware needed to manipulate, regulate, produce, and transport oil and gas to surface is designed during the completion planning process. This process as well as the sand-face completion planning requires a substantial amount of time. Unfortunately, while much thought and effort are dedicated to upfront and intermediary practices, the process required for finishing the completion; i.e., the landing string, often does not receive the same consideration.
