Maximizing hole conservation while optimizing well economics in bothconventional and deepwater wells is a continual challenge. Solid expandabletubular systems address this challenge and others by applying technology thatprovides significant solutions.
Solid expandable tubular systems have been installed in both openhole andcased-hole wellbores since November 1999. These installations occurred in avariety of well environments on land, offshore, and in deepwater to solve amyriad of drilling and completion challenges.
This paper will discuss case histories in depth by describing drilling challenges surrounding the use of solid expandable tubular technology and theconditions leading to the use of this technology.
The fundamental concept of expandable casing is cold-working steel tubulars to the required size downhole. This process, when exactingly controlled, can bemechanically preformed in a down hole environment. Many technical andoperational hurdles have to be overcome when using cold-drawing processes in adownhole environment.
Solid expandable systems are solid steel jointed pipe that are run in thehole as normal casing and expanded downhole to a pre-determined outsidediameter (OD) and inside diameter (ID). Once the system is expanded, the entiresystem will withstand published collapse and yield pressures.
Once the solid expandable system is put on depth, an expansion cone is usedto permanently mechanically deform the pipe (Fig. 1). The cone is movedthrough the expandable string by a differential hydraulic pressure across thecone area, by a direct mechanical pull or push force, or by a combination ofboth. The differential pressure is created by pumping through an inner-stringthat is connected to the cone. The hydraulic force acts across the bottom sideof the cone area forcing it upward. Mechanical force is applied by eitherraising or lowering the inner-string (Fig. 2). The progress of the conethrough the expandable tubular string deforms the steel beyond its elasticlimit into the plastic region, while keeping stresses below ultimate yield (Fig. 3). Expansions greater than 20%, based on the ID of the pipe, havebeen accomplished. Most applications using 4–1/4 in. to 13–3/8 in. tubularshave required expansions less than 20%.
A launcher at the bottom of the solid expandable tubular system houses anexpansion cone and a float shoe. The launcher is constructed of thin-wall, high-strength steel that consists of a thinner wall thickness than theexpandable casing (Fig. 4). The OD of the launcher can be up to thedrift diameter of the previous casing or liner so it can still be trippedthrough the base casing. The thinner wall allows for the cone OD to bemaximized.
The expandable system uses an elastomer joint to both seal and anchor thesystem. The elastomer joint incorporates multiple elastomer sections that arebonded to the pipe using a compression molding process. The rubberizedelastomer materials are selected to meet the temperature requirements of thegiven installation.
As the elastomer joint is expanded, the elastomer sections are energized asthey are cladded into the base casing. A designed compression ratio of theelastomer sections between the expanded pipe and the base casing gives theelastomer joints their sealing and load-bearing capabilities.
A hanger joint is positioned at the top of the expandable liner for openholeapplications and serves as both the hanger and the liner top seal. In thecased-hole installations, one elastomer joint is run immediately above thelauncher and another at the top of the liner string. In this fashion, the lowerelastomer joint anchors the liner at a selected depth while the upper elastomerjoint completes the seal of the designated interval.