Critical Advantages of Casing DrillingWed, 01/25/2012 - 09:04
After investing five years and US$25 million, Tesco Corporation took the concept of casing drilling from concept to proven technology. The idea is simple: rather than using a drill pipe to drill the well, the standard oilfield casing is used instead. Once the well is drilled, the casing is simply left in place. Bottomhole assemblies, including drillbits and other downhole tools, can be retrieved by wireline inside the casing, thus eliminating drillstring tripping and its associated challenges and problems. It is believed that drilling can be speeded up by between 20% and 30% as a result.
In the drilling industry, time is a crucial factor because of its link to expense. Less time spent drilling also means less time for problems to occur. In terms of instantaneous penetration rate, casing drilling is similar to conventional drilling techniques. However, the fact that casing pipes are longer than drill pipes means 25% fewer connections are required, which in turn means less circulating and backreaming at connections. Another feature of casing drilling is its built-in advantage of improved well control, especially important as well configurations and reservoir conditions become more complex. Most well control incidents occur when tripping drill pipe, the act of pulling the drillstring out of the hole or replacing it, usually performed because the drillbit has dulled or must be replaced for other reasons. Because the need to remove and reinsert the drillstring is eliminated with casing drilling, so are many well control incidents.
According to Tesco, the company that has pioneered casing drilling technology, the costs associated with adapting to this new drilling technique are not as high as it might first appear. Almost any drilling rig can be adapted to use casing drilling technology. Rigs with existing top drive systems can be easily converted, either temporarily or permanently, by installing a wireline system to retrieve oil tools from inside the casing. Rigs without top drives can have temporary top drives installed. Converted rigs lose none of their conventional drilling capacity.
However, because a drilling rig no longer needs to handle drill pipe, a casing drilling rig only needs a Range III single mast, which makes for a smaller rig that can be moved in fewer leads, and because it requires less horsepower, it uses less fuel and therefore produces fewer emissions.
Wellbores drilled with casing drilling are also more stable compared to conventionally drilled wellbores. With casing drilling, a new process takes place around the wellbore, generating a strengthening eect, as 20% of cuttings going up the annulus are smeared around the wellbore by the rotary casing, bridging fractures and strengthening the wellbore. This eect has been demonstrated in integrity leak o tests immediately below the previous casing point at wells drilled using casing drilling.
The casing drilling technology has several levels, from level 1, reaming pre-drilled wellbores, to level 4, retrievable liner drilling. For this reason, the construction process is gradual, moving up from level to level. The technology has been implemented eectively by many international companies and at present, Pemex is successfully using level 2 case drilling at some of its oshore wells.
Field experience in the early 2000s proved casing drilling to be a viable alternative, and since that time Tesco has worked to make casing drilling a possibility in soft, horizontal and directional wells and also vertical wells. As drilling environments get more complex and average field sizes decline, Tesco hopes that the uptake of casing drilling will continue in both Mexico and around the world.
“Tesco Casing Drilling is a globally proven technology with over 3.5 million feet drilled. It delivers all the functionality of conventional drillpipe drilling with greater eciencies and improved safety. As the industry leader in casing while drilling, Tesco continues to set world drilling records. Whether oshore or onshore, drilling vertical, directional, or horizontal wells, Tesco’s proprietary technology drills and cases the wellbore in a single trip, eliminating non-productive time.”
-Hugo Morán, VP & General Manager Latin America Business Unit of Tesco Corporation