Abstract
Abstract It is important to predict the Equivalent Circulating Density (ECD) of fluids as closely as possible for safe drilling and completion of wells. This is especially true for those challenging wells where the margin between hole collapse and formation fracturing is very narrow. These characteristics of narrow safe drilling windows are commonly seen in extended-reach drilling (ERD) and deepwater wells, and pose significant drilling and cementing challenges. Over recent years, the changes in ECD caused by fluid compressibility, downhole fluid rheology, drillpipe eccentricity, and rate of penetration have been widely studied. In contrast, work on the modeling of drillpipe rotation effects on pressure drop and ECD have received relatively little attention. Early studies have looked at the relationship between circulating pressure drop, especially in slimhole drilling configurations, and at very high drillpipe rotational speeds. More recently the predicted effects of rotation on ECD in concentric and eccentric wellbore geometries have been studied and model improvements have been made. These technical approaches are summarized in this paper. The effect of drillpipe rotational speed on the predicted ECD for different drillstring combinations are presented and discussed. The calculated effects of drillpipe rotation on pressure drop and ECD are compared to actual field measurements using downhole annular pressure gauges. From the results discussed in this paper, the reader can gauge the accuracy of the current calculation methods. The changes in ECD with drillpipe rotation can now be better predicted, something especially important for those wells whose safe drilling window is narrow. Ultimately this reduces drilling and completions risk and helps assure safe and efficient well construction.
Published Version
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