Case Histories Verify Long-Term Operational Integrity of New Nonelastomeric Sliding Sleeves in All Wellbore Conditions
Authors: Welch William R. , Ray Thomas W. 
Published: December 2007

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 challenged designers of downhole completion equipment for a number of years. One of the primary problems in these wells has been the erosion that sealing systems subjected to high pressure equalization have exhibited. 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 can 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 capable of providing the necessary long-term degree of sealing efficiency required for many applications. New completion technologies that require sliding sleeve devices for high pressure/high temperature (HP/HT) applications or for applications in which high pressure equalization of tubing and annulus pressure continue to be developed. Thus, the need to develop sealing integrity for the more corrosive conditions has also increased. Developmental efforts have finally succeeded in providing an enhanced sealing system that can meet these needs. A new sliding sleeve device that employs an innovative nonelastomeric sealing system capable of maintaining completion integrity in systems that must withstand high temperature and rigorous equalization of pressure will be the primary topic of this paper.

The case histories discussed will provide data that illustrate the capabilities of the new sleeve in many types of completions and will show that the sleeves have provided long-term integrity and reduced maintenance requirements. In analysis of production potentials and cost efficiency, these benefits are significant in the planning of developmental strategies.

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. In offshore installations, equipment that can maintain integrity and provide the capability to selectively produce from one or more zones with a single parent wellbore will allow production to continue if one zone waters out. This helps to minimize the need for costly deepwater interventions. Fig. 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 Fig. 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. P. 185^