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: 1) determine ECD reduction performance; 2) establish reliability in field conditions; and 3) 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.