Intentional Wet Shoetrack Completions for Unconventional Oil and Gas Resources: Methods and Techniques

Abstract The shoetrack of an oil and gas well refers to the bottommost part of the casing string, from the bottom of the float shoe to the top of the landing collar, or to the top of the float collar if a landing collar is not used. A wet shoetrack is defined as the lack of competent cement in the shoetrack of a cemented completion string. In applications where a wet shoetrack is undesirable, the most important purpose of the shoetrack is to allow fluid to flow out of the casing string (casing to annulus) but prevent fluid from entering (annulus to casing). Control over fluid flow direction is achieved by multiple redundant one-way check valves installed in the shoetrack that only allow flow from casing to annulus. The one-way check valves also prevent the cement from flowing from the annulus and into the casing at the end of the cement job in a phenomenon called U-tubing. This occurs because the cement has a higher density than the displacement fluid resulting in a differential pressure acting from the annulus to the casing. The ability to prevent fluid from entering the casing string, together with other equipment such as a blowout preventer, enables well control while installing and cementing the casing string. A wet shoetrack in oil and gas well construction has historically been both unintentional and undesirable. In the best case, it was a minor inconvenience, while in the worst case it was a critical Health, Safety and Environment (HSE) risk. Costly remediation operations, such as a cement squeeze, might have been required to establish a competent shoetrack before continuing with subsequent operations. The practice of completing the production casing strings in low-permeability unconventional oil and gas formations with intentional wet shoetrack completions started to take off in the early 2010's in the USA, especially on 4-1/2″ liners in the Bakken Formation, but soon also in the DJ-Basin, Permian and SCOOP/STACK formations. The growing popularity was driven by the need to cost-effectively pump down the first stage of plug and perf completion, and the significantly reduced well control risk compared to higher permeability conventional oil and gas formations. Intentional wet shoetrack completions soon became a real alternative to tubing conveyed perforation, sand jetting, and pressure-actuated atmospheric ("air") chamber sliding sleeves ("toe sleeves") to create the injection path for the first stage of plug and perf completion. This paper aims to describe the different methods and techniques used to create intentional wet shoetracks on longstring and liner production casing strings in low-permeability unconventional oil and gas formations.