A Technique of Selecting the Optimal Values of the Parameters of the Hydraulic Monitoring Holes of Drilling Bits

Abstract

It is known that through improvements in the performance of the process of cleaning (from drilling chips) of the well bottom and the drilling bit cutting structure it is possible to increase the mechanical speed and, consequently, drilling effi ciency. Cleaning is performed by feeding washing fl uid into the bottom zone through the hydraulic monitoring holes of the drilling bit. The number and orientation of these holes are determined on the basis of design experience and data on the operation of different modifi cations of a given model of a drilling bit. The structure of the fl ow of the washing fl uid in the well-bore face zone is complicated, with eddies and stagnant zones, which may lead to limitations on the evacuation of drilling chips by means of ascending fl ows and the formation of sediment on elements of the drilling bit cutting structure. Through an analysis of the structure of the fl ow of washing fl uid in the hydraulic monitoring channels and in the bottom zone, it is possible to establish the drawbacks in the construction of the washing system of the drilling bit and estimate the dynamic effect of draining jets on the back of the well bottom and the effi ciency of the nozzles used in the hydraulic monitoring holes [1–4]. The selection of an optimal design of the confi guration and orientation of the hydraulic monitoring holes of a drilling bit on the basis of results of mathematical modeling represents a complex problem. Thus, it is necessary to vary numerous geometric parameters (the diameters of the holes; the angles that govern the direction of drainage of the jets; the coordinates of the holes on the surface of the drilling bit) to fi nd the optimal combination of these parameters, a process that takes much time. Moreover, it is important to determine the optimality criterion of the washing process. For example, an increase in the speed of the ascending fl ow in the hole clearance does not indicate any improvement in the quality of the washing, since the portion of the fl uid refl ected by the walls of the well, the crest of the drilling bit and the elements of the drilling bit cutting structure may be drawn into longitudinal eddies, as a consequence of which the drilling chips will not be completely removed from the bottom zone or will immediately enter the hole clearance. Once the factors that directly infl uence the cleaning of the drilling bit cutting structure and the bottom zone from drilling chips have been determined, it is then necessary to parameterize these factors and determine the extremal values of the parameters. Through the use of the proposed technique, it is possible to formulate an optimization problem, where the result of a solution of the problem are the values of the diameters of the hydraulic monitoring holes and their position and orientation