Correlations and Analysis of Cuttings Transport with Aerated Fluids in Deviated Wells

Abstract

Abstract A study of cuttings transport at intermediate inclinations using aerated fluid, to determine the amount of solids that exist in the wellbore and minimum flow requirements for ‘clean-hole’ condition is presented. The experimental program included over 300 tests, performed with a large-scale facility (flow loop 100-ft in length, with 8" OD casing and 4.5" OD drillpipe). The angles of test section inclination were 30°, 45° and 60° from vertical. Four pipe rotational speeds (0, 40, 80, and 110 rpm) were used for different liquid and gas flow rate combinations. New correlations were found to estimate the required critical gas flow rates for hole cleaning at specified liquid flow rate and drill pipe rotation combinations, and to predict volumetric cuttings concentration as a function of air and water flow rate, drill pipe rotational speed and inclination angle. Introduction In recent years, two goals of oil and gas production companies have been to develop new methods to improve hydrocarbon recovery in mature areas and to exploit new low-pressure, low-permeability reservoirs. The use of underbalanced and near-balanced drilling techniques has found applications for these particular cases. Cuttings transport is one of the major factors affecting cost, time and quality of directional wells. The significant advantages related to drilling with aerated fluids are reduced by inefficient cutting transport to the surface. Specifically, these advantages depend on understanding the interaction between fluids and the drill cuttings. Cuttings transport with multi-phase fluids is dominated by many variables, and the interaction of all of these variables adds complexity to this subject. Due to this fact, an experimental approach has been selected to accomplish this investigation. The understanding of cuttings transport with multi-phase fluids is very limited because the majority of research in cutting transport has been conducted with conventional drilling fluids. The study of three-phase flow is relatively new, and there are not enough studies that consider the transport of solids with Newtonian gas-liquid mixtures, pipe rotation and the slip between phases. This paper reports on an experimental study of hole cleaning with aerated fluids at intermediate hole angles considering drillpipe rotation.The main results of this work are experimental data, empirical correlations and observations. It is intended to serve as a guide to the current technology, explaining how and why the effect of pipe rotation is related to the cuttings concentration in the wellbore. History In recent years, with the improvement of drilling technology, underbalanced drilling has become popular and the effect of drill pipe rotation on cuttings transport for this kind of drilling condition has begun drawing more attention in the industry. The following review focuses on cuttings transport with aerated fluids, and the effect of pipe rotation on cuttings transport in drilling operations. Multiphase (gas-liquid) Flow in Pipelines and Annuli Taitel et al.1 studied in 1980 five distinct flow patterns for vertical upward flow: slug, bubble, dispersed bubble, churn and annular flow. Shoham2 confirmed in 1982 the flow patterns identified by Taitel for inclined pipes. Barnea3 presented in 1987 a unified method of predicting flow pattern in pipes, covering the entire range of inclinations. Gómez et al.4 developed in 1999 a unified mechanistic model to predict flow pattern, liquid holdup and pressure drop in wellbores and pipelines. This model covers the entire range of inclinations. In 2000, Sunthankar5 reported on the flow of aerated fluids through large - scale horizontal and inclined wellbores. The main objective of his study was to better understand two - phase flow in annuli. The experimental study consisted of two - phase (air - water and air - polymer) fluid flow experiments in a large-scale annulus in horizontal and inclined positions, with and without drill pipe rotation. He introduced a modification of Taitel and Dukler two-phase flow model for the case of horizontal and nearly horizontal flow, and of the model developed by Gómez et al. for the other inclinations.