Expandable tubular technology

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Expandable tubular technology is a system for increasing the diameter of the casing or liner of an oil well by up to 30% after it has been run down-hole.

Challenges

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Two challenges facing the Oil & Gas industry are accessing new reservoirs that currently cannot be reached economically and maintaining profitable production from producing older fields. Expandable tubular technology is considered one of the most revolutionary technologies that has benefited the oil and gas industry during the last 10 years. The development of this technology was initiated by the industry need to reduce drilling costs, increase production of tubing constrained wells and to enable operators to access reservoirs that could otherwise not be reached economically. Expanded casing applications concentrate on reducing the telescopic profile of well designs through a downhole tube expansion process. Wider applications of the technology exist for example water shut off, and casing repairs in old wells.

Telescoping well design

To understand the enormous potential value of expandable tubular technology one must first understand the concept of telescoping well design and the constraints it places on conventional drilling.

During the planning stages, one of the primary considerations that the well engineer takes into account is the density (or "weight") of the drilling fluid. It must be heavy enough to suppress any pressured fluids contained by the rock (thus avoiding a blowout), and light enough to avoid breaking down the rock itself. Both parameters generally increase with depth, and create a window between which the drilling fluid density is safe. However, the mud density required to suppress fluid pressures at 9000' would usually break down the formation further up the well at 1000'. Therefore, the well is drilled in sections by running casing strings to cover depth ranges between which the required mud densities are suitable for the entire range. However, each bit must be smaller than the previous casing string, which in turn has to be smaller than the previous hole.

This requirement of well design creates a well where each hole section is ever-decreasing in diameter. The only conventional way to combat this effect is to start with an enormous hole at the top (sometimes 30") in order to run five casing strings and still end up with a 6" hole in the targeted reservoir. And this well design leaves little room for error: if the drillers are forced to run a casing string on account of unexpected formation pressures then the target formation may be impossible to reach. Thus there is an enormous carrot in a casing system that loses minimal - or possibly no - diameter while still isolating a whole section. Many current systems have the aim of producing a monobore well, that is, a well with a single diameter from top to bottom. But the shallow wells can the drilled with uniform diameter.

Technology

File:FEATubular.jpg
Image of Expanded Tubular FE Analysis

To reduce the loss of diameter each time a new casing string or liner is set, a cold working process has been developed whereby the casing or liner can be expanded by up to 20% in diameter after being run down-hole.

For this purpose, an expansion tool that exceeds the inner diameter of the tube by the required amount of expansion is forced through the pipe. This is done either hydraulically, by applying mud pressure, or mechanically, by pulling the conical/tapered expansion tool. The expansion needs to be reliable, when expanding several thousand feet below the surface. This can be from 30–6,000 ft in length.

Applications

The applications can be groups into two main categories – Cased hole and Open hole. Cased hole work is mainly down during the work over or completion phase of a well. The open hole products are used during the drilling period of a well.

The products developed and available today in cased hole work are the expandable liner hanger and the cased hole clad. The expandable liner hanger is basically an evolution of existing equipment currently used in the oil industry, a product with better thru bore and envisaged higher reliability. The Case hole clad provide a casing patch across a damaged section of casing, or to close off previously perforated casing. This product has two main advantages – minimal through bore loss [basically two times the wall thickness of tubular being expanded] and high pressure integrity performance.

Open hole applications is where expandable technology brings real advantages to the operator. Currently the products available are open hole liner and open hole clads.

See also

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