Wellbore pressure management is a critical part of normal drilling practices, where static and dynamic fluid pressures are used to contain formation pressures and to assure wellbore stability. Excessive fluid pressure while circulating can create problems including reduced operating margins between fracture and pore pressures and, in the extreme, lost circulation. To address these problems, an Equivalent Circulation Density (ECD) Reduction Tool (RT) has been developed.
The ECD RT is designed to counter the frictional pressure effects that exist while circulating. The tool is expected to have a broad range of drilling applications including the narrow pore/fracture pressure margin deepwater environment, wellbores prone to instability, pressure depleted reservoirs and extended reach wells.
The tool has the potential to:
Improve wellbore stability.
Extend hole intervals and reduce casing requirements.
Improve rate of penetration (ROP).
Reduce lost circulation.
Reduce differential sticking.
Improve hole cleaning in extended-reach drilling (ERD) wells through the use of higher flow rates.
This paper describes a new downhole tool for ECD reduction, which is run as an integral part of the drill string. A prototype tool has been built, to operate inside 10-3/4″ to 13-3/8″ casing strings, which has undergone testing in a flow loop and in two experimental wells. The design features of this prototype and the test results obtained so far are discussed in this paper.