Qualification and Use of a Self-Equalizing Subsurface Safety Valve in Large-Bore, High-Rate, Gas-Well Applications in the Middle East
Authors: Swan Tom , Cooper Scott 
Published: May 2011

The desire to use 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 a gas-exploration and production industry challenge. To this end, many operators have implemented the use of large-bore, high-rate gas wells for effective development of the world's prolific gas fields. One of the key components in this type of completion is the subsurface safety valve (SSSV), because it has a primary role in containment of the hydrocarbon should a well-control loss event occur. The SSSV is critical to the protection of the lives, assets, and the environment in the surrounding vicinity of the well completion.

During normal operations or after a well-shut-in event occurs, pressure must be equalized across the SSSV closure device; typically, a flapper device to reopen the valve and return the well to production is used. 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. This feeling has evolved from the traditional feeling that passing the large volumes of gas through a self-equalizing feature would be detrimental to valve long-term reliability in large-bore applications.

When using a non-self-equalizing SSSV, the supply of tubing pressure to equalize the pressure across the flapper must be introduced above the SSSV from the surface, and in many situations, this may not be operationally efficient or economical. Conversely, if a self-equalizing-type SSSV could be installed in a large-bore gas completion, there would be significant benefits, which would include:Reduction in capital expenditure for surface-pressure equipmentOperational simplicityHSE 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 benefits resulting from the use of these valves.

Introduction

Although an economic downturn occurred as this decade was coming to an end, some of the world's basic needs increased, and natural gas was one of them. Natural gas is considered now as a vital component of the energy supply equation. In 2007, global natural gas consumption was 108 trillion scf. According to the US Energy Information Administration's International Energy Outlook 2010, natural gas usage is projected to rise to 156 trillion scf by 2035, which is an overall increase of 44%. Many countries are now looking for methods to increase their non-associated gas production in order to fuel their domestic growth, which is greater than their present gas-production capabilities.

From an oil-and-gas-industry perspective, this growing demand places a premium on efficient natural-gas extraction; however, the economic reduction has demanded that more efficient production methods be initiated. 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. In high-rate, large-bore wells, conventional wisdom suggested that a TRSV with no built-in feature for equalizing shut-in pressure across the closure device when the tool was to be reopened be used. This paper will highlight the efforts of a safety-valve manufacturer and a Middle East operator to qualify and install large-bore safety valves containing a self-equalizing feature in high-rate, large-bore, natural-gas wells.