Abstract

The concept of using natural gas as an energy source has increased to such an extent that there has been a notable worldwide increase in its usage. Supplying this growing demand has been an industry challenge. To this end, many operators have implemented the use of large-bore, high-rate gas wells for effective development of gas fields. One of the key components in this type of completion is the subsurface safety valve (SSSV) because of its primary role of containing the hydrocarbon in the event a well loss should occur. The SSSV is critical to the protection of the lives, assets, as well as the environment in the surrounding vicinity.

During normal operations or after a well shut-in event, pressure must be equalized across the SSSV closure device, typically with a flapper, to reopen the valve. Because of the relatively high volumes of gas carried in the production tubing of a large-bore completion, non-self-equalizing SSSVs have been the product of choice. Traditional wisdom was that passing the large volume of gas through a self-equalizing feature would be detrimental to valve long-term reliability.

The use of a non-self-equalizing SSSV requires the capability to supply tubing pressure above the SSSV closure device, which may not be operationally efficient or economical. Conversely, if a self-equalizing-type SSSV could be installed in large-bore gas completions, there would be significant benefits, which include:

  • Reduction in capital expenditure for surface pressure equipment

  • Operational simplicity

  • HSE benefits

This paper will discuss the collaboration between a Middle East operator and the SSSV supplier to qualify a large-bore subsurface safety valve with a self-equalizing feature for use in high-rate gas-well applications. It will also review field implementation and resulting benefits with the use of these valves.

Introduction

The world economy is becoming increasingly reliant on natural gas as a vital component of the energy supply equation. In 2000, global natural gas consumption was 88 trillion ft3. Usage is predicted to exceed 125 trillion ft3 by 2015, which is an overall increase of 42%. From an oil-and-gas industry perspective, this growing demand places a premium on efficient natural gas extraction. To meet this challenge, the use of large-bore completion architecture in prolific gas reservoir applications is being employed to effectively exploit a reservoir's potential. To protect the people, environment, and investments in these developments, a tubing retrievable safety valve (TRSV) is placed in the production tubing to automatically shut in the well below the surface in the event that well control is lost. For these high-rate, large-bore wells, conventional wisdom suggested the use of a TRSV with no built-in feature for equalizing shut-in pressure across the closure device when the tool was to be reopened. This paper will highlight the efforts of a safety-valve manufacturer and Middle East operator in the qualification and installation of large-bore safety valves containing a self-equalizing feature in high-rate,

large-bore natural gas wells.

Self-equalizing features in TRSVs have been available for many years. With improvements in technology and the inherent reliability of these devices, the percentage of TRSVs employing an equalizing feature has steadily increased to where over 95% of TRSVs installed in general completions with 4½-in. production tubing size or less use this feature. The selfequalizing feature is much less often employed in deepwater offshore and large-bore, high-rate gas applications.

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