Casing-running system helps take casing to TD in highly deviated, unstable formations
By Aaron Dauphine and Scott Sivewright, Weatherford International Ltd
As industry ventures into more challenging and remote locations to recover oil and gas reserves, a high-quality well architecture is paramount for achieving maximized production, safety and efficiency. While new tools and technologies provide a key piece of the solution, it’s also important to use an engineered, multidisciplinary approach to the well construction process. Increasingly deep, highly deviated and extended-reach wells that 10 years ago could not have been drilled or completed are becoming commonplace – but operations remain complex. Older wells that present instability issues frequently require workovers and innovative solutions to extend production.
For these complex fields, collaborating with service companies early in the well development process to apply an integrated approach can be beneficial.
Earlier this year, a casing-running system used in conjunction with a specialized floating technique was deployed to run and set casing in a difficult extended-reach and extreme high-angle well from a platform rig off the coast of Southern California. Nearly 20,000 ft (6,096 meters) of casing was installed in 28 hrs, requiring rotation torque of more than 65,000 ft-lbs of torque.
For a mature, deviated gas well offshore Italy, casing-running and cementing technologies were combined in a workover operation to run more than 8,600 ft (2,621 meters) of casing in an unstable wellbore with tight hole conditions. Both the casing-running and cementing jobs were completed safely with significant time and cost savings.
Although the two wells posed different challenges, in both cases, performance-enhancing technologies were deployed alongside a collaborative and multidisciplinary philosophy to enhance the economic and technical viability of the wells.
Over the past decades, advances in casing-running technology have paved the way for more efficient well construction. The OverDrive top-drive casing-running and drilling system introduced in 2005 attaches to the rig’s top drive and combines many conventional casing tools into one system. It extends the functionality of the rig’s top drive from drill pipe to casing, enabling simultaneous rotation; reciprocation/push down; and circulation of the casing string.
Adding a reaming shoe or drillable casing bit to the casing string makes it possible to ream in a pre-drilled section, extend through problem zones or drill hole sections with the casing string.
This opens a range of options to increase drilling efficiency and reduce NPT. These capabilities facilitate casing-running and cementing in deep, extended-reach and high-angle wells and in older, problematic wells where tight hole conditions and unstable formations can impact long-term production.
Once top-drive casing running technology proved viable, it was apparent that focusing on making connections at the rotary alone was limiting. The real value was in expanding the scope of the tubular-running business to consider all processes involved in bringing high-integrity casing strings with the planned diameter to TD, and a secure wellbore over the life of the well.
The goal of improving the ability to land casing strings at the desired depth has driven a need for earlier collaboration between the service company and the operator. In the past, reaming and drilling with casing has typically been used to address problems as they occur. A new practice of early collaboration with engineers trained in the unique challenges of reaming, drilling and cementing operations when rotating casing strings took form. This approach makes it possible to preemptively and more efficiently deal with drilling hazards before they become a critical issue.
Optimizing Well Architecture
A well construction project for a major operator in offshore Southern California involved a novel solution for constructing a well that presented a significant challenge – to run 9 5/8-in. casing in a highly deviated, extended-reach well that could not be constructed using conventional methods. The casing string would be installed at a measured depth of 19,900 ft (6,065 meters) from the platform to TD, and at a true vertical depth of just 6,500 ft (1,981 meters), the well had deviations up to almost 90°. In addition, high downhole frictional forces meant the casing could be set in the well only by rotating it in with significant torque applied.
Because the distance from the rig floor to TD was so long and the well presented such high angles and frictional forces, Weatherford’s 750-ton heavy duty casing-running system was used to “float” a string as far as possible, then apply weight and rotate and push down the casing. The floating operation kept the casing buoyant and overcame friction in the long, deviated hole. Burst disc collars were used so the casing could be filled with mud at a later point in the operation.
While running to 18,880 ft (5,754 meters), the casing string weighed 290 tons and required 100% of the string weight to move it through the difficult hole conditions to TD. The last 20 joints, roughly 800 ft (243 meters), were rotated down into the hole to get the casing to TD. While deeper platform wells have been constructed using this technology, this particular well was unique because of the amount of torque required to rotate the casing. Up to 69,000 ft-lbs of torque was used to rotate the joints down, and between 45,000 ft-lbs and 60,000 ft-lbs were required to maintain rotation at 35-40 rpm. Each of the last 20 joints took 20 min to rotate and ream to the bottom of the well.
The casing-running operation took 28 hrs, saving the operator considerable time and cost in achieving an optimal well architecture that otherwise could not have been accomplished.
Combining the right technologies when appropriate also can enable operators to better meet overall wellbore objectives. The same casing-running system was used in conjunction with a top drive cementing head for a workover operation on a mature, somewhat deviated, tight-gas well with a measured depth of just over 8,600 ft in the Adriatic Sea off the east coast of Italy. The well, which typically undergoes a workover operation every four to five years, is characterized by sand and clay that presents stability issues for the customer, a multinational oil and gas company.
In this case, the operator wanted to run the 9 5/8-in., 53.5 ft-lbs premium casing string safely and quickly to the planned depth, then efficiently transition from casing-running to cementing operations to improve cement placement, avoiding stability-related problems. Due to the well conditions, the operation required a casing-running system that would allow a quick cement job once the casing string reached TD and rotation during a slurry displacement.
For the operation, the casing-running system was deployed in conjunction with the torque driving tool to run the casing and overcome the tight hole and instability issues, including differential sticking, in the 12 ¼-in. hole. Use of the tool eliminated the need for conventional casing tongs. The system ran 8,625 ft (2,630 meters) of casing to the bottom of the well at an average of 10 joints/hr. A torque-turn system also was deployed to measure and analyze the torque on the turn of the connections.
The top-drive cement head line, incorporating a swivel with a side port cement line and dart-and-plug system, was assembled on the casing string for the cement job. Although the conditions in the well prevented the ability to rotate the casing string, the torque driving tool was able to simultaneously circulate, push down and reciprocate the entire casing string in five- and 10-meter increments throughout the cementing process, successfully cementing the casing string in the wellbore. The torque driving tool also maintained tension on the casing string as the cement set, eliminating the need to hang the well off, thus reducing NPT.
The entire operation was completed in two days without incident. It was the first application of the casing-running system in Italy and the first to combine the system with a top drive cementing head. The method provided greater assurance than conventional methods that the wellbore would not collapse. The efficient installation of the pre-assembled, top-drive cementing head saved significant time by eliminating the need to rig down the casing-running system or rig-up conventional cementing equipment.
The approach has been deployed worldwide in a variety of offshore and land operations, from US shale plays to the Caspian Sea. Applications include an offshore well in Mexico where a high-angle section of a well was drilled with liner to isolate a problem section and reach the target zone. For a well in Trinidad, two critical hole sections were drilled and cased to mitigate unstable formations in conjunction with loss zones.
In the Caspian Sea, the system was integrated with a rotating and hoisting cementing head to help minimize equipment rig-up time and enable rotation and reciprocation of the casing string during cementing. The integrated solution improved zonal isolation and reduced mud and cement losses, resulting in a reduction of transition time between the casing torque running and cementing operations.
The emergence of game-changing well construction technologies and earlier service provider-operator collaboration has taken the industry to new depths by optimizing well architecture through improved zonal isolation, friction reduction and cement operations in well environments that pose significant challenges for the industry. These technologies, combined with an upfront, collaborative, multidisciplinary approach, can help operators achieve TD by providing a strategy to effectively deal with risk and/or economic uncertainty and the technical limitations of drilling wells.
Choosing the right technology and effectively deploying tools and methods that work together can result in construction of a secure wellbore, ultimately resulting in enhanced long-term production.
OverDrive is a trademarked term of Weatherford International Ltd.