Ask the experts: How innovation proves an enabler for through tubing rotary drilling

explains how it was used in Norwegian subsea wells, where the world’s first four TTRD operations from floaters were recently carried out.

TTRD is a technique where new/stranded pockets of oil are accessed by drilling through an existing well bore. The main benefit of this technique is that the functionality of existing wells remains undisturbed hence dramatically reducing the associated well construction costs in some cases by as much as 50 percent. In many cases, this technique is the only economical way of accessing these stranded reserves.

As the drilling is performed through the existing completion, great care must be taken to avoid damage to the downhole completion components, particularly the down-hole safety valve (DHSV). Damage to the DHSV can require the retrieval of the entire completion string, resulting in all the economical benefits of the original operation being lost.

Historically, specially designed sleeves were constructed to protect the DHSV during wireline/slickline interventions. These were then subsequently upgraded to facilitate coil-tubing operations. However, both systems were never intended to handle drilling operations and as a consequence were a lightweight solution to a ‘heavyweight’ problem.

Onshore testing subsequently revealed that the original protection systems were not fit for purpose and it was at this point that Red Spider Technology was contacted with a view to providing a solution.

As a consequence of this immediate need, Red Spider Technology designed and constructed a pioneering TTRD safety valve protection system that is purpose built for drilling operations. The sleeve is mounted on a running tool that forms part of the drill-string, and is deployed and retrieved in ‘piggy-back’ fashion each time the drill-string enters the well.

Extensive onshore testing demonstrated that the Red Spider Technology protection sleeve would not rotate during drilling operations. This is extremely important as even a small rotation of the protection sleeve during drilling operations may result in damage to the safety valve.

The protection system positively locks into place in the safety valve profile and approximately 10tons of force is needed to shear it out and leave it behind as the rest of the drill string runs into the well through the sleeve. Once drilling operations have been completed the string is retrieved and on the way out of the hole, a specially designed pick-up shoulder will engage the sleeve, releasing it with an over pull of about 12tons. All shear rings and shear studs are designed to be contained in such a way as to avoid dropping any pieces of these into the well. This again represents a major improvement over earlier systems.

A special pulling tool has also been designed to pick up the sleeve on a separate run should that be necessary, e.g. if the drill string has experienced a twist off leaving the running tool down hole. Special hard facing materials have been applied to the running tools to further reduce wear on the completion during these interventions. The wear on running tools is also reduced; in a recent operation a 1mm wear on the running tool was observed after 1.6 million rotations of the drill string.

Of the four well operations to date, all have had 7inch completions installed. However, based upon the recent successes in Norway, a UK customer has committed to a Red Spider Technology TTRD DHSV protection system for a five and a half inch completion. This will be a first in that particular size.

Meanwhile, an existing customer in Norway was so pleased with the results of its subsea wells operations that the company has now committed to similar systems for use on its platform wells, upgrading from the older traditionally deployed technology.

Feedback from the drill crews is also very encouraging. They find the system efficient and easy to use. The redress procedure carried out by Red Spider Technology personnel onsite between each run, ensures that shear out and pick up weights observed give the drillers absolute confidence that the system is actually locked in and retrieved correctly.

Close cooperation with operators has led to a number of ingenious design features on something that was considered dumb iron in the past, and the industry in Norway is now recognizing that the protection of safety valves during well operations had been lacking in the past. One example is the development of a Crown Plug Profile Protection Sleeve (CPPPS) that can be run in tandem with the DHSV Protection Sleeve, hence avoiding a separate run to install.

Red Spider Technology presented its success with the TTRD protection sleeve system at the ONS exhibition in Stavanger in August 2006, and anticipates great interest from customers around the world.

Red Spider Technology was formed in 2003 to develop tools to meet the new challenges faced by the global oil and gas industry. With bases in Houston, Dubai, Scotland and Norway, the company supplies products and services which add value by reducing client operating time, production costs and environmental risks. Red Spider has a range of tools for flow control, artificial lift and through-tubing drilling applications. More information about Red Spider can be found at www.redspiders.com or by calling Gary Smith on + 1 281 657 3320