Expandable Tubular Technology - Telescoping Well Design

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.