A Simplified Method for Prediction of ECD Increase with Drillpipe Rotation

Abstract

The ability to accurately predict the effect of drillpipe rotation on Equivalent Circulating Density (ECD) remains a challenge for those involved in engineering today's complex wells. In many of these challenging wells (extended-reach drilling, deepwater, HPHT, etc.), the safe drilling window between hole collapse and fracturing is often narrow. Accurate prediction of the effect of drillpipe rotational speed could allow better optimization of operational parameters in the drilling process, and hopefully reduce the incidence of violation of the safe drilling window.Recently ECD results measured at different circulation rates and drillpipe rotational speeds were modeled and presented to the industry. The calculation methods involved several complex factors including estimated drillpipe eccentricity, nonlinear shear rate modeling coefficients, drillpipe geometry correction factors, etc. The presented results constituted the best-available correlation with direct downhole pressure measurements, but still showed improvement was needed.Further development work has been done in this same area to reduce the complexity of the calculations and yet improve modeling accuracy. It was noticed that the effect of increasing drillpipe rotational speed at a constant annular velocity produced a near-linear increase in ECD. In addition the ratio of the internal diameter of the hole or casing and the outer diameter of the drillpipe (Di/Do) was found to be a meaningful modeling parameter that could transcend explicit values of estimated drillpipe eccentricity. Data from the earlier work and some additional field results were then reworked using the new calculation scheme, which is presented in the paper. The results presented in this paper show that this calculation technique can produce better prediction of field measurements of downhole pressure changes while rotating and is much simpler to use. Not only can it help in navigating through the safe drilling window, but it also can be used to separate pure rotation effects from other coupled wellbore events, such as hole cleaning and barite sag.

The Effect of Drillstring Rotation on Equivalent Circulation Density: Modeling and Analysis of Field Measurements

“…Unlike the results from the majority of the laboratory studies, most of the field measurements (Delwiche et al 1992;Ward and Andreassen 1998;Isambourg et al 1998;Charlez et al 1998;Green et al 1999;Hemphill et al 2007;Hemphill et al 2008) have shown a significant increase in pressure loss as the pipe rotation increases. The discrepancy between lab observations and field measurements can be attributed to several factors, such as drillpipe wobbling or instability, the irregular geometry of the wellbore, tool joint effect, or a combination of these factors.…”

“…The measured and predicted pressure loss ratios vary from 1.05 to 1.23 indicating significant increase in annular pressure loss with the increases in the rotation speed. Furthermore, the accuracy of the new model is compared with the existing model developed by Hemphill et al (2008). When tested with the data from Well C, the new model shows better accuracy than the existing one (Fig.…”

Annular Frictional Pressure Losses During Drilling—Predicting the Effect of Drillstring Rotation

“…Unlike the results from the majority of the laboratory studies, most of the field measurements [22][23][24][25][26][27][28][29][30] have shown a significant increase in pressure loss as the pipe rota tion increases. The discrepancy between lab observations and field measurements can be attributed to several factors, such as operat ing with multiple dimension scales, drillpipe wobbling or instabil ity, the irregular geometry of the wellbore, tool joint effect, far too simple fluid systems in the laboratory or a combination of these factors.…”

Simulation of Drilling Pressure Profile in Directional Drilling and User Program Development

“…Although, a study of flow behavior when pipe is rotating is still complex especially in drilling operation, there are several literatures proposed empirical correlations and mechanistic models. Hemphill et al [4] developed the general equation for increased pressure loss with rotation in term of diameter ratio and rotation speed (rpm) as expressed in (8)…”

“…A deviation of predicted data are compared with measured data in every recorded depth. The less statistical value of deviation gives more accurate result, so it is obvious that the combination of Blasius formula and increased-pressure-loss equation proposed by Hemphill et al (2008) (Model B1) can accurately estimate downhole pressure in practical field in both stationary situation and rotating drillpipe. On the other hand, decreasing annular gap width will increase pressure loss.…”