Challenges of Designing HP/HT Equipment
- Karen Bybee (JPT Assistant Technology Editor)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- April 2008
- Document Type
- Journal Paper
- 92 - 94
- 2008. Society of Petroleum Engineers
- 1 in the last 30 days
- 62 since 2007
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This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 109999, "The Challenges of Designing HP/HT Equipment," by Andrew Forsyth, SPE, Expro; Brian Saucier, DeepMar; Daniel More, Expro; Ray A. Stawaisz, Chevron; Dave Gill, Stress Services; and Ray Younger, Prospect, prepared for the 2007 SPE Annual Technical Conference and Exhibition, Anaheim, California, 11-14 November.The paper has not been peer reviewed.
The full-length paper presents an overview of the main design activities for a completion and intervention landing-string system. The functional- and structural-design challenges encountered because of the high operating pressures and temperatures are reviewed. Analysis tools were used to quantify the observations found during testing, and subsequently to assist in determining a design solution. A key aspect of the design process was viewing the design and operations from a holistic perspective by evaluating the design throughout its operational life.
The full-length paper details the technical challenges of developing a high-pressure/high-temperature (HP/HT) completion and intervention landing-string system for the Tahiti field in the Gulf of Mexico (GOM). Because the project presented some specific operational challenges, traditional analytical methods were insufficient for the design process and a comprehensive test and qualification program was required to validate that the equipment proposed was fit for purpose. The full-length paper presents an overview of the design methodology adopted and how the results from finite-element modeling assisted in validating the test program.
Fig. 1 shows a typical subsea landing-string configuration within a blowout preventer (BOP). The hydraulic-controlled functions of the subsea test tree (SSTT) are the following.
- To provide a dual-barrier well-isolation system during completion and intervention operations.
- To allow coiled tubing (CT) and wireline access into the well and to cut CT and wireline in an emergency situation without compromising pressure containment.
- To disconnect the upper landing string from the SSTT by means of a latch mechanism.
- To retain hydrocarbons in the landing string in the event of shear or planned disconnect.
- To provide a method of closure of the BOP rams on special joints for HP well integrity.
The SSTT comprises the latch assembly, dual fail-safe closed ball-valve assembly, and a slick-joint assembly to facilitate closure of the BOP pipe rams.
With the introduction of subsea horizontal trees in the mid-1990s, landing-string systems were developed for well-completion and -intervention operations. Early landing strings were designed to operate at maximum differential pressures and temperatures of 10,000 psi and 250°F, respectively. With the discovery of significant hydrocarbon reserves in deep water, the challenge to develop economically viable equipment had been set. Along with the requirement for HP/HT applications, the locations and environment that landing strings are required to operate in have become significantly more arduous. The HP/HT landing string also was required to be controlled with a subsea electrohydraulic control system for the deepwater application as opposed to earlier systems that were operated hydraulically from surface.
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