Abstract

Significant technological advances in methods and equipment have permitted increased drilling in deeper waters, often beyond continental shelves. Completion techniques have also advanced to allow efficient deepwater production. When designing a deepwater or subsea completion, traditional downhole challenges are complicated by subsea wellhead conditions that require advanced practices and equipment. This paper will acquaint the reader with characteristics unique to deepwater, subsea completions and present new completion accessories that maximize performance throughout the life of the well. Included will be a case study of a new use of electronics, dynamic seal assemblies and deepwater subsurface safety systems by an operator in deepwater Gulf of Mexico.

Introduction

When considering deepwater exploitation, not only are the issues of wellhead changed, but also downhole equipment must be modified due to surface and ocean floor conditions. In the design and installation phase of the completion and subsequent life of the well, the presence of certain design parameters and the ease of installation must be considered as well as how any future stimulation, intervention or workover will be accomplished and/or accommodated. This paper will put forth thought processes that must go into a subsea completion design and present a deepwater completion typical of those being used in the Gulf of Mexico.

Tubular design

Tubular design must address some unique aspects of a subsea completion. In addition to wellhead placement on the ocean floor, many wells are highly deviated to horizontal, with obvious impact on tubular and production string design.

Stimulation. The tubular design must address any future well intervention or stimulation modes. The stimulation mode differs in a subsea completion from that of a surface completion. Temperature versus depth, from the surface, increases in a linear fashion in most surface or shallow water completions (Fig 1).

The subsea completion temperature increase is not linear. As fluids are pumped from the surface, they are cooled by surrounding waters until the wellhead depth is reached, at which time the temperature versus depth begins to increase in a linear fashion (Fig 2).

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