Cuttings Transport With Foam Under Simulated Downhole Horizontal Conditions

Abstract

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 99201, "Experimental Study on Cuttings Transport With Foam Under Simulated Horizontal Downhole Conditions," by Z. Chen, SPE, R.M. Ahmed, SPE, S.Z. Miska, SPE, N.E. Takach, SPE, M. Yu, SPE, and M.B. Pickell, U. of Tulsa, and J. Hallman, SPE, Weatherford Intl. Ltd., prepared for the 2006 IADC/SPE Drilling Conference, Miami, Florida, 21–23 February. The use of drilling foams is increasing because foams exhibit properties that are desirable in many drilling operations. A good knowledge of cuttings-transport efficiency under downhole conditions is essential for safe foam drilling. Previous cuttings-transport studies with foam were limited to low-pressure and ambient-temperature (LPAT) conditions. An experimental study of cuttings transport with foam in a horizontal annulus was performed under simulated downhole conditions. Introduction Foam drilling fluid can provide low density as well as flexibility in equivalent-circulating-density (ECD) control. However, the complexity of foam flows makes it difficult to obtain reliable predictions of ECD for foam drilling. When drill cuttings are in the wellbore, the foam/cuttings mixture affects bottomhole pressure, making the complicated compressible foam flow even more complex. Therefore, cuttings transport with foam should be well understood for accurate bottomhole pressure and ECD estimation. Studies on cuttings transport by foam fluids are limited. Although cuttings in foam affect hydraulics calculations and ECD predictions, it is generally accepted that foam cuttings transport in vertical wells is very efficient. Foam-flow velocity of 120 ft/min is sufficient for most vertical-well foam drilling; in some cases, flow velocity as low as 70 ft/min has been successful. For foam drilling in horizontal wells, the particle-settling velocity is perpendicular to foam-flow direction and drill cuttings tend to settle to the low side of the wellbore. The density of drill cuttings is much higher than the density of foam. Therefore, the mechanisms that govern cuttings transport are different for horizontal wells. Empirical correlations and models developed for vertical wells may not be valid for horizontal and inclined wellbores. This research project studied cuttings transport with foam in simulated downhole conditions for more-reliable bottomhole pressure and ECD predictions. Experimental Study Experiments of cuttings transport in foam were conducted at the Advanced Cuttings Transport Facility at the U. of Tulsa. The facility is designed to investigate cuttings transport and hydraulics of both compressible and incompressible drilling fluids under elevated-temperature and -pressure conditions. The facility can simulate both pipe and annular flow at pressures up to 1,500 psig and temperatures up to 200°F for incompressible Newtonian and non-Newtonian fluids. It also accommodates compressible fluids such as aerated fluid and foams.