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The equivalent circulation density reduction tool (ECDRT) is designed to counter the increased fluid pressure in the annulus caused by friction loss and cuttings load by reducing the total hydrostatic head. The tool has a broad range of drilling applications, including: narrow pore/fracture pressure margins in deep water and their effects on casing setting-depth selection; wellbore instability; depleted reservoirs; and extended-reach wells. This paper describes progress on development and testing of a prototype ECDRT. The prototype was recently tested in a BP onshore U.S. Arkoma asset operation in southeastern Oklahoma. The primary objectives of the field trial were: determine ECD reduction performance; establish reliability in field conditions; and evaluate the ECDRT operational procedures. The test involved drilling 8.75-in. hole with the tool running inside 9.625-in. casing cemented at a depth of 4,500 ft. Performance was monitored continuously from a real-time display of surface and downhole measurements. Wellbore pressure management was clearly demonstrated in the field trial. The ECDRT consistently reduced ECD by about 150 psi, or the equivalent of about 0.7 ppg at 4,500 ft. Drilling performance was not limited in any way by the ECDRT. Fluid returns and wellbore cleaning were normal throughout the drilling operation. The ECDRT processed cuttings generated by the drilling at 100 ft/hr without difficulty. More than 500 ft of hole was successfully drilled before the tool was pulled because of difficulties with the directional drilling system. The final goal to evaluate ECDRT operational procedures was achieved as performance indicators on the surface worked reliably to diagnose the operational status of the tool. Post-well analysis showed that there were still some design issues to secure the longevity and sustained performance of the tool. The tool demonstrated the ability to manage annular pressure under actual drilling conditions. Introduction Managing downhole pressure is a critical element of most drilling jobs and becomes paramount under difficult conditions of deepwater and extended-reach drilling (ERD). The downhole pressure of circulating fluid is the sum of hydrostatic head (a function of mud density and cuttings loading) and frictional loss (a function of mud rheology, mud density, annular geometry, and flow rate). This paper describes the development of a downhole tool for reducing the ECD of circulating mud. It covers the design and testing of a prototype ECDRT that is valuable for use in managed-pressure drilling (MPD) applications, both onshore and offshore. The objective of ECD reduction is to minimize the effect of pressure loss caused by friction so that downhole pressure of circulating drilling fluid is nearly equal to its hydrostatic pressure. Some of the benefits of ECD reduction are: ability to drill challenging wells to their target depths; extended casing shoe intervals; increased safety margin between fracture gradient and actual ECD; improved rates of penetration (ROPs); and enhanced wellbore stability.1 In recent years several new technologies for MPD have been developed. Some of the new technologies for MPD are: dual-gradient drilling system2; annular backpressure control system3; continuous circulation system4,5; controlled rheological properties of drilling fluids for specific application6,7; and a downhole pump.8 The ECDRT is a portable tool that can be installed in the drillstring, as needed, by making a short trip. The ECDRT is located in the vertical section of the well, starting at less than 700 ft from the surface. This relatively shallow placement of the tool is significant, as it not only allows for rapid installation but ensures a limited effect on drilling activities. Deployment of the ECDRT requires virtually no rig-up time. Lessons learned from technology trials and successful field trials have been incorporated into the current design. The detailed results from the most recent trial in southeastern Oklahoma are presented in this paper together with the forward plan to make the technology available to the marketplace.

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