Drilling with Casing - Practical, Cost Effective and Here to Stay

Abstract

Abstract For several years, Drilling with Casing has been something of a 'Cinderella' technology, trapped between a few successful niche applications and a perceived need to fully emulate the capability of conventional drilling. Over the five years up until the end of 1999, various niche applications were successfully addressed, but the technology had not been applied economically to mainstream drilling operations. Since early 2000, developments have taken place rendering drilling-down surface casing a standard operation in several parts of the world, most notably in Thailand and Indonesia. The enabling technology has been a drillable drill bit (or 'DrillShoe'). Unlike conventional oilfield bits, which are inherently nondrillable, this tool is constructed from soft alloy and contains a cutting structure, which does not damage the next bit in the hole. The DrillShoe method is the first truly 'single -trip' technique of drilling with casing - nothing is pulled out of the hole. Casing is drilled down in precisely the same manner as conventional rotary drilling with drill pipe. When TD is reached, cementing can begin immediately. The next drill string is run in conventional manner and drills-out the shoe track and DrillShoe, without damage to the drill bit, which then proceeds to drill the next section of well bore. In the year to Jun 2001, more than 100 Drilling with Casing operations have been completed successfully with this technology. Casing sizes vary from 7 in. to 20 in., with run lengths up to 1500 feet. Case histories are presented showing the development of tools and drilling practices.