Efficient shoe track drillout is essential to reducing nonproductive operations and resuming drilling new hole after casing runs as quickly as possible. Drilling out the shoe track is often troublesome as BHAs are typically designed to drill new formation, not the shoe track itself.
Even though many operators consider drilling the shoe track a duplicated effort (as no new hole is being drilled) it is an operation that must be performed after every surface and intermediate casing string is cemented before drilling can resume.

The shoe track is the space between the float or guide shoe and the landing seat of the cementing wiper plugs. Its purpose is to ensure that the casing shoe is surrounded by high quality cement, to keep the end of the cement from becoming contaminated with drilling fluid, and to provide a pressure indication via plug bump that the cement displacement is complete.

Drilling the shoe track can go smoothly in one well, and be problematic in the next. A recent study of 90 similar wells showed that a shoe track could be drilled efficiently in 2.3 hours, but could also take as long as 14 hours. It is important to understand the key factors that affect your ability to drill the shoe track quickly and effectively.

1. Drilling through the shoe track imparts left hand torque on threaded connections. Using a good thread lock system prevents casing joints from loosening while drilling out the shoe track. This also replaces welding on the bottom of casing joints, which can cause weakening from heat and chew up valuable rig time. Our Lok-N-Load™ thread lock product is battle-tested and comes in an easy-to-mix kit complete with base resin, catalyst and putty knife.

2. Competent cement jobs are important to ensure that shoe track components are not allowed to rotate during the drilling process. Fixed cutter bits (common PDC designs) drill best on stationary targets, and this can be achieved by selecting anti-rotation shoe track components, and achieving a quality cement job.

3. Optimal WOB and RPM must be determined to achieve maximum ROP. Lower RPM can help keep the shoe track components from spinning and aid in junk removal. A low WOB helps the PDC bit cut the drillable shoe track components more effectively, while keeping cuttings small enough for effective transport. It may take some experimentation to determine the best WOB and RPM parameters for your specific application.

4. Drilling shoe tracks with Rotary Steerable Systems (RSS) is becoming common place in horizontal shale wells, as operators are increasingly turning to RSS for drilling long lateral sections. Aggressive PDC bits are often coupled with RSS, which tends to create larger sized cuttings. These larger cuttings, when combined with the larger tool diameters of RSS can lead to plugging and bridging of cuttings in the annulus. If this occurs, a reduction in ROP may follow as weight transfer to the bit is affected.

5. Transport of cuttings will be affected by the cutting size, which is related to the aggressiveness of the PDC bit and the WOB applied. Flow rate, hole inclination, fluid parameters, RPM, and cuttings size are factors that affect cuttings transport. It is best to model these parameters using commercial cuttings transport software to achieve optimal transport.

In summary, drilling out the shoe track can be problematic unless many parameters are evaluated and understood. These key factors are:
• PDC bit type and style – cutter size and angle, blade layout and bit profile
• Drilling procedures – including WOB, RPM, and flow rate
• Cuttings transport – software simulations to best understand the relationship between cutting size, flow rate, and hole cleaning effectiveness
• Target materials being drilled – drillable, non-rotating components are preferred

By understanding the parameters that affect how a shoe track drills – along with a bit of experimentation and modeling, you’ll be able to design and implement a predictable, repeatable shoe track drilling program.

Some content for this blog was derived from the following technical papers. These can be found at www.onepetro.com.

Rogers et al., 2009. Costly Shoe-Track Drilling Practices Using Conventional and Rotary Steerable Systems
Evaluated. SPE/IADC 124368

Wiktorski et al., 2016. Shoe Track Drillout Analysis: Factors Affecting Drilling Efficiency. SPE-180011-MS

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 float equipment and other drillable shoe track products, email us at info@casingequipment.com