Nonelastomeric Sliding Sleeve Maintains Long Term Integrity in HP/HT Application: Case Histories
Authors: Welch William R. , Ray Thomas W. 
Published: December 2007

Abstract
The problem of erosion that sealing systems subjected to high pressure equalization have exhibited has been a challenge to designers of downhole completion equipment for a number of years. The increase in the drilling and completion of wells between 15,000 and 20,000 feet vertical depth in pursuit of the increased production capacities associated with these deeper wells has further intensified this problem. The high pressures and temperatures inherent to the deeper environments accelerate seal degradation, and subsequently, have increased the need for more specialized sealing packages that will maintain integrity in severe service conditions.
Although the capabilities of a new generation of polymeric seal materials have been significantly enhanced, in certain extreme conditions, they still have not been able to provide the necessary long-term degree of sealing efficiency required for applications such as those requiring sliding sleeve devices for high pressure/high temperature (HP/HT) applications or applications in which high pressure equalization of tubing and annulus pressure is required.
This paper will present a new sliding sleeve device that employs a newly developed nonelastomeric sealing system that can maintain completion integrity in systems that must withstand high temperature and rigorous equalization of pressure.

Introduction
Sliding sleeves have become the preferred circulation/production device for circulating drilling, completion, or kill fluids; allowing zone selectivity; or eliminating tubing perforating. Many new types of drilling and completion techniques have been developed to take advantage of the sliding sleeve isolating capabilities that allow separate or commingled production from many zones. Examples of this are seen in some of the new horizontal completion configurations and in the multilateral techniques in which a lateral liner is connected to the vertical parent casing in such a way that sealing efficiency to enable selective flow control is provided at the junction of the two.
Figure 1 illustrates a typical sliding sleeve used to circulate kill fluid and allow production from alternate zones. Sliding sleeves have evolved from very simple "one shot" devices to a variety of configurations that have been designed to meet specific conditional criteria for a variety of applications. Earlier versions had no landing profile for flow controls and minimal concern for cyclic operation. Today, however, since sliding sleeves must be considered not only for routine circulation and production but also for annular or tubing hydraulic operation and complex flow paths for injection-operated jet pumps, more sophisticated equipment has been needed to meet the more specialized scenarios. (See Figure 2.)
Three major components have been common to all designs, however. These include 1) a body that is integral with the tubing string, 2) an internal sliding sleeve for controlling fluid flow, and 3) a sealing system to pack off the sleeve/body interface. Unfortunately, the last item, which has been critical to maintaining system integrity, has continued to plague designers of downhole completion equipment for many years - particularly when dealing with high pressures and elevated temperatures. Proper selection of seals or sealing systems for oil and gas production necessitates a comprehensive knowledge of the chemistry of both the seal material(s) and the conditions of the environment in which the seals will be used. While this sounds as if this knowledge easily enables sealing systems to be designed for purpose, the problems of compromise of seal integrity have been extremely difficult to resolve.

Background
To control fluid flow between the tubing bore and casing annulus, sliding sleeves are opened and closed by wireline or coiled-tubing manipulation of the internal sliding sleeve that is spanned by a pair of seal stacks.
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