"Gas migration" has been the catch phrase of the Appalachian Basin in the northeastern part of the US for years. As demonstrated in a previous study, optimal displacement efficiency can be obtained by rotating casing during the entirety of the cement operation, providing uniform cement coverage and eliminating gas migration. However, while horizontal well lengths continue to increase, the ability to maintain rotation for the entirety of the cement operation can be severely inhibited.
Conventional cement slurries are satisfactory for the majority of wells in both the Marcellus and Utica/Point Pleasant. However, while operators are pushing the limit toward a 20,000-ft measured depth, there is a growing need to rely less on industry best practices written at the onset of shale drilling and expand engineering creativity toward implementing new technologies. With rotation off the table, a service company recommended the combined use of two highly enhanced mechanical property cement slurry technologies to bridge the technology gap from a conventional cementing solution to a more "life of the well" solution.
Historically, gas migration from either the Upper Devonian and/or the Marcellus Shale has been proven to be troublesome for the northeastern part of Pennsylvania. When the challenge cannot be addressed with historical best practices, deploying new technology on hand is necessary to achieve the goal. With the more robust functionality of a low-Portland cement design and resin composite cement slurry, the service company's design team was able to combine these two technologies to deliver a dependable barrier tailored to achieve zonal isolation. Optimizing the placement of the resin-composite-based cement slurry itself was pivotal; placement across the problem zones and above the landing point of the horizontal section was necessary. Successful elimination of both pre- and post-fracturing gas migration was achieved without casing rotation during cement slurry placement. The wells were put into production, and the operator has not had to perform any costly remediation operations because the reservoir was properly isolated by means of the primary cementing operation.
Enhanced mechanical property cements were proven to be vital for alleviating the concerns of gas migration. These cement systems help prevent Upper Devonian and Marcellus wells from being reworked because of primary cement quality post-completion.