Subsea Re-Injection of Drilled Cuttings - Operational Experience

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractSubsea re-injection of drilled cuttings has been applied on the Åsgard field to handle oil wet cuttings. For various reasons, oil based drilling fluids have been used in all 12 ¼" and 8 ½" sections at Åsgard. Discharge of oil wet cuttings is not permitted. Cuttings have to be re-injected to the formation or sent onshore for treatment. Onshore treatment and logistics, are expensive and involve a large emission of CO2. If reinjection can be performed, big bag handling operations are significantly reduced. Furthermore, it is difficult to have reliable logistics to bring cuttings onshore. Therefore, cuttings re-injection is the optimum solution for this operation, where the preferred injection point is below the 20" casing shoe.Re-injection is straightforward if cuttings can be reinjected into a formation underneath a large sand formation where the liquid phase of the slurry can leak off. At Åsgard there are no such large sands. Therefore, cuttings have to be re-injected into shale formations. Since the fluid does not leak off sufficiently fast in shale there is a danger that the annulus may be exposed to a too high pressure for a long time. If too large a fluid volume is injected at a time, there is a danger that the fluid may propagate as a fluid bubble to the surface.Leakage to surface has been observed four times at Åsgard. It has been recognized that the cementing results must be better than normal to hinder leakage to surface if cuttings are re-injected into shale formations without sand layers. This paper describes the leakages in detail. It focuses on the necessary improved drilling and cementing precautions to hinder leakage. The paper also describes a technique with alternating re-injection and static periods to make the liquid phase leak off into minor sands and shale, preventing the formation of too high an annulus pressure and hindering the formation of a fluid bubble propagating to the surface.

Propuesta de Actualización del RAOHE Incorporando Tecnologías de Fracturamiento Hidráulico, Reinyección de Recortes y Revisión de Límites Permisibles en la Gestión de Descargas Líquidas

“…Finalmente, una vez que el diseño de la operación está en su lugar, es necesario monitorear las operaciones activamente. El control de calidad y los ajustes de propiedades reológicas y físicas específicas del sitio son cruciales para mantener la integridad de la operación y completar con éxito el proyecto (Abou-Sayed & Guo, 2002;Saasen et al, 2001). Los parámetros que deben considerarse dentro del monitoreo incluyen, el registro continuo de las propiedades de la lechada inyectada (composición, concentración, densidad, etc…), de la presión de fondo y durante la inyección y en los periodos prolongados de cierre y el análisis del comportamiento de la formación y la fractura durante la inyección y cierre (Bruno et al, 2000).…”

Challenges for Monitoring and Verification of Drill Cuttings Reinjection Performance

“…8,9 Several release incidents of injected slurry to the environment due to inadequate cementing have also been reported. 10 One operator, after injecting over 800 million pounds of waste slurry in one well, decided to halt the injection process to avert communication to the surface when the cuttings path intersected an existing open conduits to a near-by well. It is imperative that a well-defined monitoring and verification program be properly implemented to ensure the integrity of the operation and the safe containment of the disposed waste.…”