Development of a Subsurface Reverse Circulation Tool System to Cement Weak and Depleted Zones in Deepwater Formations

摘要

Reverse circulation cementing is a placement technique that reduces bottomhole equivalent circulating densities (ECDs) and reduces lost circulation risk in wells in which conventional circulation pressures would break down formations. Until now, reverse circulation cementing has been performed only on land or in shallow-water wells in which the annulus was accessible from the surface to pump down. This paper describes the design, development, and validation of technology that enables subsurface reverse circulation. Gaps in technology have made it challenging to transfer reverse-cementing-placement techniques to primary cementing operations in deepwater. To reverse cement a liner, fluids must be pumped down the work string to prevent potential contact inside the riser and blowout preventer (BOP), and then fluids must be injected into the annulus downhole while full circulation continues. A tool system was developed to facilitate this unique flow path, provide alternative methods to set liner hangers, and provide flexibility for contingencies and other operational requirements. The developed subsurface reverse circulation tool system uses radio frequency identification (RFID) technology so that the tools can be operated remotely and repeatedly either by RFID tags or through surface-pressure pulse sequences. Three RFID-activated tools were designed: a circulation tool, a crossover tool, and a downhole flapper. The prototype tool system was first evaluated through bench testing of individual components and then through large-scale rig testing. During the rig trials, the entire system was run into a test well, and a multiday sequence of flow testing validated the function and performance of each tool. After successful testing in rig trials, the subsurface reverse circulation tools (RCT) were deployed in the Appalachia basin field, located in the Northeastern United States. This paper discusses the requirements of a subsurface reverse-circulation-cementing system. It describes the design, development, and validation of technology that enables subsurface reverse circulation. It also describes the prototype system that was built and the field testing results. This new capability enables the cement to be pumped down the work string and then to exit to the annulus at a point above the liner string.