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PETROMAKS2-Stort program petroleum

Steady displacements for conventional and reverse circulation primary cementing

Alternative title: Stasjonær væskefortrengning ved konvensjonell- og reverssirkulering brønnsementeringsoperasjoner

Awarded: NOK 6.9 mill.

Project Number:

294815

Application Type:

Project Period:

2019 - 2024

Partner countries:

Primary cementing of casing strings and liners is the operation where the drilling fluid in the annulus outside the casing or liner is displaced and replaced by a cement slurry. Once hardened, the annulus cement forms an important well barrier element that should provide zonal isolation and support the casing. In conventional circulation cementing operations, this is achieved by pumping a sequence of fluids down the well inside the casing to be cemented; at the bottom, the fluids exit the casing and flow back to the surface in the annulus outside the casing. This project has studied primary cementing using the reverse-circulation method, where cementing fluids are injected directly from the surface to the annulus to be cemented. This cementing strategy can potentially reduce the bottom-hole pressure during circulation, and thereby enable faster placement of fluids, the use of denser cement slurries, or installing a longer cement column. Reverse circulation is also relevant for cementing across fluid loss zones, where cementing fluids are bullheaded down the annulus from the surface. Consequently, reverse-circulation primary cementing is an attractive placement strategy particularly for onshore wells and wells for geothermal energy production. A challenge associated with this placement strategy, is density-unstable conditions between fluid pairs during cementing, which may increase the risk of slurry contamination. Contamination may in turn reduce the quality of the hardened cement and necessitate challenging treatment operations. This project has studied density-unstable fluid displacement in concentric and eccentric annular geometries using a combination of experimental and numerical methods, focusing on identifying strategies for improving the displacement efficiency. Typical cementing fluids and common injection rates in the field correspond to unstable displacements, with significant mixing between successive fluids. The project has found that the displacement process can be in part stabilized by increasing the imposed flow rate, increasing the viscosity of the fluids, ensuring viscosity-stable fluid pairs, and to centralize the inner casing string. Some of these strategies may however undermine perceived benefits of reverse circulation cementing. The project has focused on relatively short annular geometries, and future work should study mixing, instabilities and displacement efficiency in longer domains, for improved upscaling to field conditions.

A key impact of the project has been to increase the awareness of displacement-related challenges associated with reverse-circulation cementing, and density-unstable displacements in general, as well as providing guidance for possible strategies that partly compensate for the unstable conditions. This knowledge can benefit future reverse-circulation or bradenhead cementing operations by optimizing fluid properties to avoid channeling or back-flow of light, displaced fluid. The project has also strengthened the research collaboration between Norway and an internationally leading Canadian academic environment, and enabled an extended research stay.

Primary cementing is the well construction operation where drilling fluid is displaced from the annular space between casing or liner and formation and replaced by a cement slurry. Effective mobilization and displacement of drilling fluids are recognized as essential steps for successful cementing operations. The project addresses important knowledge needs within well cementing and the third technology target area defined by OG21, namely how process and fluid properties can be optimized in order to ensure complete drilling fluid displacement for conventional and reverse circulation primary cementing. The purpose of this project is to explore the existence and the conditions necessary for having so called steady, travelling wave displacement flows, where the interface between two consecutive fluids move steadily along the annulus toward the surface at the mean pump velocity. Such displacements are highly desirable as they ensure continuous displacement of drilling fluid around the entire annulus and thereby avoid mud channeling. We will explore the necessary process and fluid conditions for achieving steady displacements in both conventional and reverse circulation displacements using a combination of experimental work and numerical simulations. An important R&D challenge in the project will be to develop both experimental and numerical methods that allow conclusive observation of steady displacements under certain fluid and process conditions. In order to prove the existence and examine the stability of the displacement first-hand, require a long flow loop and a long numerical simulation geometry. The results can be used directly by operators and cementing service companies to design appropriate density and rheology of spacer fluids and cement slurry, flow rate, as well as minimum centralization required to achieve desirable steady state displacements.

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Funding scheme:

PETROMAKS2-Stort program petroleum