The effect of cuttings on annular pressure loss - An analysis of field data in the North Sea
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This master's thesis studies the correlation between rapid alterations in cuttings concentration and the corresponding change in pressure loss, using the standpipe pressure as pressure indicator. Drilling data from two wells in the North Sea is used when analysing the pressure effect from cuttings concentration. Intervals where there is a change in rate of penetration and standpipe pressure simultaneously, while all other relevant parameters are kept constant, are identified. Difference in standpipe pressure and rate of penetration is represented graphically in order to identify trends between the two parameters. A correlation between change in rate of penetration and the response in standpipe pressure was found for all sections. Calculations indicate that the change in pressure loss cannot solely be explained by cuttings bedding, viscosity and density changes or weight of suspended cuttings in the wellbore. Some other effect is therefore likely to be present. Empirical equations from curve fitting were obtained for each section, describing the relation between change in standpipe pressure and change in rate of penetration. The number of cases evaluated is, however, not sufficient for the empirical equations to accurately predict changes in standpipe pressure beyond the evaluated sections. A correlation between the slope of the fitted curves and the properties of each section was not identified.