Ultradeep HP/HT Completions: Classification, Design Methodologies, and Technical Challenges
Authors: Denney Dennis 
Published: February 2015

This article, written by Technology Editor Dennis Denney, contains highlights of paper OTC 17927, "Ultradeep HP/HT Completions: Classification, Design Methodologies, and Technical Challenges," by B. Maldonado, A. Arrazola, and B. Morton, Baker Oil Tools, prepared for the 2006 Offshore Technology Conference, Houston, 1–4 May.
Traditional understanding of high-pressure/high-temperature (HP/HT) applications, 10,000 psi and 300°F, is common. The HP/HT working envelope has been extended to 15,000 psi and 400°F, with some limited gaps related to completion-size availability rather than technology needs. This larger envelope is being pushed further to 20,000 to 30,000 psi and 400 to 500°F. The technology gaps associated with this new HP/HT frontier are not limited to completion equipment but include casing, tubing, blowout preventors, wellheads, perforating, lubricators, logging, and drilling.

Introduction
To identify HP/HT operating environments, as well as technology gaps, a new classification is developing that segments HP/HT into three tiers. While existing technology embraces most of Tier-1 applications, Tiers 2 and 3 demand extraordinary considerations with regard to the selection of the completion equipment. The new design methodologies and technical challenges are associated with extreme- (Tier 2) and ultra- (Tier 3) HP/HT completions on the basis of "typical" deepwater and deep HP/HT gaswell parameters, casing, and tubing programs.
Evaluation and recommendation of methods for selecting completion equipment, including sand control, subsurface safety valve, packer-to-tubing interface, production packer, and flow-control technologies, were reviewed. The completion of extreme- and ultra-HP/HT wells involves high risk and high rig costs that demand special considerations and investments. Completion-technology gaps for these HP/HT wells are outlined. Also highlighted is the importance of upfront planning, design, qualification testing, quality assurance and control, and contingency options.

Classifications
Major HP/HT projects are developing in the North Sea and the Gulf of Mexico (GOM). The learning curve has been very steep on key completion technologies including high-strength steels, nickel-based corrosion-resistant alloys, and sealing compounds.
To help identify HP/HT operating environments, safe operating envelopes, and technology gaps, a new terminology is developing. As Fig. 1 shows, the terminology segments HP/HT operations into three tiers. Tier 1 refers to wells with reservoir pressure up to 15,000 psi and temperature up to 350°F. Most HP/HT operations to date have taken place under Tier-1 conditions. Tier-2 wells are the extreme-HP/HT wells characterized by reservoir pressures up to 20,000 psi and/or temperatures up to 400°F. Many ongoing developments in the North Sea and upcoming HP/HT deepwater gas/oil wells, particularly in the GOM, fall into the Tier-2 category. Tier 3 encompasses ultra-HP/HT wells, with reservoir pressures up to 30,000 psi and/or temperatures up to 500°F. Tier 3 is the HP/HT segment with the most significant technology gaps. Several deep gas reservoirs onshore North America and on the GOM shelf fall into this category.