ABSTRACT:

The first step in the traditional hydraulics optimization process is to determine the recommended flow rate based on given mud rheological properties. This flow rate should fall within physical limits for the well and simultaneously maximize a selected optimization criterion. Bit nozzles (or total fluid area) are then sized so that circulating losses match the desired pump pressure. Recent work has demonstrated that the optimization process can be improved if mud rheology is considered as a product rather than an input. This paper presents a refinement of this work as a method and a computer program that consider the many complications of downhole conditions. One of the opportunities of this approach is the possible identification of unique rheological properties that can only be generated by a new family of drilling fluids or additives. Well-known constraints for drilling hydraulics optimization include drilling margin based on fracture gradient and mud weight, hole-cleaning requirements, pump hydraulic power, downhole tool limitations, pump limitations, and wellbore erosion. These restrictions create two distinctive hydraulic windows bounded by flow rate and pressure limitations. Downhole mud density and rheology based on temperature and pressure profiles help define these boundaries. The primary goal of the process described in this paper is to determine Herschel-Bulkley rheological properties (measured at the surface) and flow rate required to satisfy defined optimization criteria and constraints. The hydraulic window concept is described to illustrate how the software works internally. Examples are included to demonstrate sensitivity to various conditions and parameters

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