As operators design wells with increasing lateral lengths and longer horizontal sections, running casing to TD has become more challenging. The longer the lateral, the more drag and friction forces impede the process of pushing casing to bottom. The majority of today’s shale play wells use cased hole completions to optimize wellbore integrity and ensure the success of fracturing operations. Therefore, the prevention of downhole problems when running casing, and the need to get casing to total depth (TD) is extremely important.
Wellbore geometry is also a consideration when determining how to run casing to bottom and choosing the best method for reducing friction and drag. Typical horizontal shales well in the US have build rates between 6 – 12 degrees/100 ft. and are designed to reach the target formation with a minimal amount of Horizontal displacement (step-out) from the wellhead. This geometry increases the load put on casing at the heel of the well, and can result in buckling if drag and friction factors are excessive.
Several techniques have been devised to increase the chances of success on long horizontal casing runs. These include rotating the casing, adding buoyancy to “float” the casing to bottom, and employing devices to introduce axial vibration.
Rotating Casing to Bottom
Rotating casing to bottom changes the friction coefficient from one that is static to a dynamic component. The dynamic component is considerably less that the static component, allowing available casing weight to be used in penetration. In high drag scenarios, this method may require the use of torque-shouldered premium connections where the casing can be rotated under load without fear of joint failure. While there is an additional cost associated with using casing with premium connections, this can prevent unplanned connection failures during the running process.
Buoyancy Effect
The concept of floating casing to bottom is also a widely-used option. Casing floatation uses air or light fluid trapped in the lower section of the casing string to create a buoyant chamber on the casing’s lower end. This can significantly reduce the casing weight resting on the wellbore, reducing drag and friction during the casing running process. The length of the buoyant chamber can vary based on the reduction in drag required to successfully run the casing to TD. The inability to circulate through the casing prior to reaching TD is a major limitation of this technique. The wellbore must be well conditioned prior to running casing to avoid issues presented by static mud gelation. If a washout, ledge, hole collapse, or sloughing shale is encountered, it may prove difficult to pass even with the benefit of floatation.
Axial Vibration
To overcome the challenges with getting casing to bottom in horizontal wells, new tools are being introduced that induce downhole axial vibration to overcome friction. This concept has been widely used successfully in both coiled tubing and rotary drilling applications and greatly reduces the frictional forces between the drillpipe or coiled tubing and the wellbore, while improving toolface control, sliding ROP, and extending bit life. In casing applications, introducing axial vibration reduces the forces while running casing, allowing higher doglegs to be traversed, and longer laterals to be cased completely and quickly. Operators have also seen improvements in cement integrity, as the vibration during casing running operations improves cement flow and the uniformity of cement placement, reducing voids and channels.
Citadel Casing Solutions has partnered with Thru Tubing Solutions to provide the proprietary Casing XRV™ tool for extended reach horizontal wells where casing running may be problematic. This tool is positioned in the casing string near the shoe, and is designed to induce substantial axial vibration to reduce friction forces and improve casing running ability. As fluid flows through casing and the Casing XRV tool, a fluid pulsation is created at the tool’s exit point. This changes hydraulic loading at the end of the casing, creating a continuous fluid hammer effect that improves casing installation. An added benefit of utilizing the Casing XRV tool is the improvement in cement integrity by reduced voids and channels as a result of the induced vibration. The Casing XRV is also not flow restricted prior to reaching TD as is floatation, allowing circulation while running in hole.
The robust and reliable Casing XRV tools incorporate no moving parts, and contains no elastomers. It is available in a wide range of threads and sizes. Larger sizes are made of drillable material, and can easily be drilled out by conventional PDC bits. In today’s horizontal wellbores, integrating the Casing XRV tool into your casing program can significantly reduce problems with getting casing to bottom, while improving the quality of the cement job.
About Citadel Casing Solutions
Citadel Casing Solutions produces innovative technology for cementing casing equipment. We create customer value through our unmatched engineering expertise, broad base of experience, and overall responsiveness. Our goal is to deliver the ultimate in wellbore integrity to protect our customer’s assets.
For more information on the Casing XRV, email us at info@casingequipment.com