No abstract

Knowledge of the distribution of pressure losses is a key factor to the design of a slimhole well. However, predicting annular pressure losses-the major partis difficult because drillstring motion makes nonnegligible complex contributions that have not been accounted for up to now.

Knowledge of the distribution of pressure losses is a key factor to the design of a slimhole well. However, predicting annular pressure losses-the major partis difficult because drillstring motion makes nonnegligible complex contributions that have not been accounted for up to now.Flow in

No abstract

Accurate prediction of annular flow is of primary importance in slimhole drilling. A model was developed that better represents actual amular configurations. It accounts for axial variations of drillpipe eccentricity and for effeets arising from drillpipe rotation. The model is validated with data obtained from 3 industrial slimhole wells (4''3/4 and 3"3/8 phases). Based on model predictions, guidelines are given to define flow parameters and to adapt fluid rheology in order to obtain optimal hole cleaning under safe drilling conditions. introduction Flow in the reduced annular geometries of slimhole wells may give pronounced pressure losses at moderate or even low flow rates, generating thus substantially higher equivalent circulating densities than in conventioml wells. Accurate control of wellbore hydraulics and adequate choice of fluid rheology and flow parameters are therefore imponant issues of the slimhole teehrwlogy, as far as avoiding excessive pressure against the formation and efficient hole cleaning are comerned.Early field practice ] and more recent laboratory studies2 showed that the usual hydraulic models are not able to correctly predict pressure losses in slimhole armuli. These models assume a concentric annular geometry and ignore drillpipe rotation. However, the flow is extremely sensitive to the precise boundary conditions, so drillpipe actual configuration and rotation must be accounted for3.