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We study displacement flows involving pairs of Newtonian and shear-thinning fluids in vertical annular geometries using experimental and computational methods. This investigation is motivated by the primary cementing of casing strings, which is part of the well construction operation. In displacement scenarios that involve density-unstable fluid pairs, it is well-known that buoyancy can increase the inter-mixing between fluids and hence contaminate cementing fluids due to gravity-driven instabilities. Our study seeks to investigate how the imposed flow rate, the degree of inner pipe centralization, and the viscosity of the fluids affect the displacement efficiency in such cases. The study complements our recent paper [R. Zhang et al., “Vertical cementing displacement flows of shear-thinning fluids,” Phys. Fluids 35, 113110 (2023)], which focused on density-stable configurations, and here we consider the more challenging, density-unstable displacement flows. Our experiments and three-dimensional computational results are in general agreement. The results show that displacements improve for viscosity-stable conditions, i.e., when the displacing fluid is the more viscous fluid. Characteristic fingering patterns occur in the interface region of the fluids for viscosity-unstable conditions. The eccentricity of the inner pipe is seen to promote the channeling of fluids, and viscosity-unstable conditions can exacerbate this effect further. A degree of stabilization of density unstable displacements can be achieved by increasing the imposed flow rate and the viscosity of the fluids while maintaining a stable viscosity ratio.
We study displacement flows involving pairs of Newtonian and shear-thinning fluids in vertical annular geometries using experimental and computational methods. This investigation is motivated by the primary cementing of casing strings, which is part of the well construction operation. In displacement scenarios that involve density-unstable fluid pairs, it is well-known that buoyancy can increase the inter-mixing between fluids and hence contaminate cementing fluids due to gravity-driven instabilities. Our study seeks to investigate how the imposed flow rate, the degree of inner pipe centralization, and the viscosity of the fluids affect the displacement efficiency in such cases. The study complements our recent paper [R. Zhang et al., “Vertical cementing displacement flows of shear-thinning fluids,” Phys. Fluids 35, 113110 (2023)], which focused on density-stable configurations, and here we consider the more challenging, density-unstable displacement flows. Our experiments and three-dimensional computational results are in general agreement. The results show that displacements improve for viscosity-stable conditions, i.e., when the displacing fluid is the more viscous fluid. Characteristic fingering patterns occur in the interface region of the fluids for viscosity-unstable conditions. The eccentricity of the inner pipe is seen to promote the channeling of fluids, and viscosity-unstable conditions can exacerbate this effect further. A degree of stabilization of density unstable displacements can be achieved by increasing the imposed flow rate and the viscosity of the fluids while maintaining a stable viscosity ratio.
Deepwater operators continually face technical and environmental challenges to drilling and completing wells safely and efficiently. To address both current and future challenges, the industry has leveraged radio frequency identification (RFID) technology to reduce risk, rig time, and nonproductive time (NPT) and to perform operations that traditional tools cannot perform. RFID technology has been integrated into drilling and completions tools to improve performance and reduce risk for offshore operations, such as drilling underreamed holes, spotting lost circulation materials, setting packers, opening stimulation sleeves, and performing subsurface reverse cementing. These tools use RFID tags released from the rig floor to enable downhole hydraulic power units (HPUs) to operate the tools. This paper describes criteria for selecting RFID-enabled tools rather than traditional tools, integration of RFID tools with operations, and value-added features enabled by RFID. Contingency, safety, and risk assessment factors are discussed, along with case studies validating performance and suitability of selected RFID tools. Three case studies describe how RFID solutions for drilling and completions were selected and applied in high-cost environments to address specific challenges and job objectives. Design and bench testing of RFID tools to enable future subsurface reverse cementing operations are also covered. The first case study describes an RFID lower-completion system that was successfully deployed into a southern North Sea extended-reach well. The system enabled remote control of flapper isolation valves and remote operation of stimulation sleeves to access the reservoir, which aimed to eliminate the need for intervention between treatments and ultimately improved fracture cycle time and reduced risk. In the Gulf of Mexico, an RFID drilling underreamer was used to set a liner shoe precisely at the casing point and eliminate a dedicated hole-opening run that would have been needed with traditional underreamers. The 8 1/2-in. hole section was drilled; but losses prevented the mechanical reamer from opening. Therefore, the 650-ft hole section was drilled to TD using the bit only. To eliminate multiple trips to take pressure samples and underream the hole section to 9-7/8 in., an RFID underreamer was placed below the measurement-while-drilling/logging-while-drilling (MWD/LWD) equipment. After pressure measurements were taken, the underreamer was actuated with RFID tags to enlarge the entire 650-ft openhole section with less than a 13-ft rathole. In the last case study, an RFID circulation sub was deployed above other bottomhole assembly (BHA) components, including an RFID underreamer and a conventional ball drop underreamer. This configuration enabled the operator to ream out the 22-in. cemented show track, underream the openhole section, and efficiently clean the wellbore at total depth. Because of BHA and standpipe pressure limitations, the RFID circulation sub was used in a split-flow application to bypass a percentage of the total flow to allow for a higher downhole flow rate. The sub helped to achieve high flow rates, high annular velocity, and turbulent flow, which contributed to better hole cleaning and improved wellbore integrity. Selecting the best tools and technology for specific applications results in streamlined applications and reduced operational risk. The methodology for selection, design, planning, and implementation of RFID drilling and completions tools identifies when RFID technology can be beneficial to deepwater operations.
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.
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