SPE Drilling & Completion
Volume 21, Number 4, December 2006, pp. 279-286

Summary

Narrow pore-pressure/fracture gradient windows often necessitate additional casing strings to maintain wellbore stability and reach deeper objective depths. Operators are constrained by the number of strings of conventional casing that can run through subsea or surface wellhead equipment. Planning solid expandable tubulars into the well design allows the operator to run additional casing strings to reach deeper objectives. Traditionally, there are two approaches used in selecting expandable tubular technology: one selects a solid expandable tubular for use as a contingency and installs it after encountering problems, often deep in a distressed well; and the other installs a large-bore expandable in the upper section of the well as part of the base well design.

Using a solid expandable tubular system in the upper sections of the well design preserves hole size from the onset and allows more casing strings to be run without pushing casing points to the fracture-gradient limit. Preserving hole size contributes to drilling efficiency, reduces equivalent circulation density (ECD), and minimizes risk associated with small-hole size in deeper sections of the wellbore.

Another application for solid expandable tubulars is in conjunction with surface blowout preventer (BOP) stack technology. Typical surface stack systems are drilled using a subsea stack BOP system coupled to a 13³/₈-in. or 16-in. high-pressure drilling riser. After setting the riser, only one or two conventional casing strings can be run through the riser, which limits chances of drilling to deeper geologic objectives.

This paper looks at two case histories. The first case history compares two deepwater offset wells in the Mississippi Canyon area of the Gulf of Mexico (GoM). One well used expandable casing as a contingency late in the well execution phase, and the other well incorporated the expandable casing as part of the base design in an upper-hole section. The second case history evaluates a well in which solid expandable tubular technology allows up to three additional casing strings to be run in a surface-stack application. This paper discusses how combining solid expandable tubular technology with surface-stack technology pushes the technical limits of surface-stack drilling into deeper water and deeper formations.

Introduction

Adding value to any drilling design requires the deliberate, objective, and thorough assessment of known factors, as well as a plan for risk management of uncertainties. Methodical planning enables operators to design the “most likely to succeed” approach that employs the most appropriate technology. But even the best-laid plans can be disrupted by unanticipated conditions, resulting in a deviation from the drilling program design that can jeopardize the ability of the well to reach key objectives. Generating a well design to reach production zones with viable economics requires a strategic approach that addresses known factors as well as prepares for the unexpected, such as lost circulation, differential sticking, and abnormally pressured zones that can cause abrupt changes in wellbore conditions, resulting in a bust in the original well design.

© 2006. Society of Petroleum Engineers

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History

• Original manuscript received: 15 November 2004
• Revised manuscript received: 18 April 2006
• Manuscript approved: 6 June 2006
• Version of record: 20 December 2006