The efficiency of the drilling process is largely governed by the efficiency with which the available hydraulics removes rock chips created by the mechanical action of the bit. To date, a physical understanding of the process associated with the hydraulic removal of the chips remains unknown. Rock chips mechanically freed from the parent rock by the drilling action of the bit are generally held in place by overbearing pressures. These pressures must be overcome either by hydraulic action or by mechanical regrinding before the chip may be removed. This work presents the experimental results of a study designed to examine the effects of dynamic forces brought about by jet turbulence on the removal of loose rock chips. Synthetic chips of known shape and size, embedded in a simulated hole bottom and held in place by hydrostatic pressure, were removed solely by the jetting action of a vertically impinging jet. The synthetic chips were flush-mounted into the plate, rendering the shear forces on the surface of the chips at least two orders of magnitude less than the hold-down forces. Measurements of the static jet-impingement pressure and the dynamic fluctuating pressure caused by the jet turbulence were related to turbulent time-scale measurements made using a laser Doppler anemometer, producing an analytical tool to predict the necessary conditions for chip removal. Tests were conducted in both water and an optically clear synthetic clay mixture having non-Newtonian viscosity characteristics similar to a bentonitic fluid. The results indicate that chip hold-down forces can be overcome by the turbulent action of the jet nozzle. Correlations are given indicating the conditions necessary (i.e., jet standoff, radial chip location, chip size, and viscosity) to permit chip removal. These results can be used to place and size jets optimally to maximize chip remov2.l and bottomhole cleaning.
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This paper presents the results of a study to determine the ability of commercially available mechanical aids called' 'turbulators" to alter the flow profile and thus enhance the displacement efficiency of typical cementing operations. Results are presented for both the predictions and the measurements showing the effects of pump rate, viscosity, density, and turbulator blade geometry on the induced flow angle along the pipe axis (thus effective swirl length). The results indicate that mud-displacement efficiency can be improved dramatically with mechanical aids that alter the flow profile in the annulus between the casing and the hole. Simple guidelines are provided for spacing turbulators, and two case histories are presented that substantiate the laboratory findings.
Conventionalroller cone bit hydraulicsoptimization techniques focuson minimizing circulation lossesto deliver maximum poweror impact forceto the bit. Little emphasis has been placedon opdmizing the bottomhole cleaning processby itself, eventhough it is highly influential in both penetration rate and bit life. Optimization of bit and bottomhole cleaning requires the elimination or minimization of flow stagnation in the open spacesbetweentheroUingcones sndtheenhancement of shear flowand turbulent preamres across theholebottom. Better mkstadng of this flow opens the door for improvedbit design and better allocation of hydraulic energyto improvethe eiliciencywith which the bit and hole bottom surkes are kept free of cuttings and fines. This paper presents the results of a numerical study of the highly twbulen$ threedimensionsl flow surroundingan 8 1/2" IADC 517 class roller cone rock bit. The computationswere performedusing a threedimensiona.1finite elementcomputer code(N3S). Numericalpredictionswereverifiedby fidkscale laboratoryexperimentsconsisting of Wetpaint flow visualizationtests on the exposedaurkes of the bit high-speed photogmphyof plastic particles to determine flowVelocitiesand measmments of the mean and fluctuating presmres on the boreholebottom.A similar approach has been used successtMlyto improve References and illustrations at end of paper 237 A nozzle arrangementsand bit geometryon easier-to-modelPDC bits. This paper verifies that the same methodologyis applicable to the more complexand highly disturbed flowsaround a roller cone rock bit and may bring about comparableimprovements.
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