Transport of Small Cuttings in Extended Reach Drilling

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractField experience has shown that inefficient transport of small cuttings is a main factor for excessive drag and torque during extended reach drilling; however, very little is known about the transport behavior of small cuttings. In this study, extensive experiments with three sizes of cuttings (0.45 mm-3.3 mm) were conducted in a field-scale flow loop (8 in.×4.5 in., 100-ft long) to identify the main factors affecting small cuttings transport. The effects of cuttings size, drill pipe rotation, fluid rheology, flow rate and hole inclination were investigated.The results show significant differences in cuttings transport based on cuttings size. Smaller cuttings result in a higher cuttings concentration than larger cuttings in a horizontal annulus when tested with water. However, a lower concentration was achieved for smaller cuttings when 0.25 ppb Polyanionic Cellulose (PAC) solutions were used. Unlike the transport of large cuttings, which is mainly dominated by fluid flow rate, the key factors controlling small cuttings transport were found to be pipe rotation and fluid rheology. Improvement by pipe rotation in the transport efficiency of small cuttings is up to twice as large as the improvement in large cuttings transport. Compared with water, PAC solutions significantly improve smaller cuttings transport, while the transport of larger cuttings is only slightly enhanced.Mathematical modeling was performed to develop correlations for cuttings concentration and bed height in an annulus for field applications. Predictions from a three-layer model previously developed for larger cuttings were also compared with experimental results. Differences (up to 80%) indicate the need for improving the frequently used three-layer model by including correlations specifically developed for small cuttings to get a better design of extended reach drilling. This study is also useful for horizontal or high-angle well drilling and completion through sand reservoirs.

Review of Hole Cleaning in Complex Structural Wells

“…Therefore, mud rheology [20][21][22][23][24], particle size [20,21,23,25,26], and drillpipe rotation [6,24,27] continued to be studied.…”

“…Duan et al [25] focused on studying three sizes of cuttings(0.45mm-3.3mm) with TUDRP's 8 inch 100 feet flow loop. These experiments were conducted with water and polymeric fluids.…”

“…In previous studies, equivalent cuttings bed height [14,25,41,42,[44][45][46], cuttings concentration [25,43], annular bed area [50], and the ratio between mass of suspended particles and initial mass of deposited cuttings [27] can be used to depict the amount of annular cuttings. As shown in Table 2 and Table 3, even more factors such as mud rheology, cuttings concentration were considered in some correlations and models, complexity of cuttings transport leads to the big gap between theoretic studies and real drilling conditions.…”

A New Mathematical Method for Solving Cuttings Transport Problem of Horizontal Wells: Ant Colony Algorithm

“…Over the past 30 years, considerable effort has been expended on solving cuttings transport problem in drilling horizontal wells. Many researchers developed various models [1][2][3][4][5][6][7][8][9][10] to investigate this problem, among which the two-layer model is one of the analytical research models and is formulated with highly nonlinear equations set.…”

Simulation on Cuttings Transport with Drillpipe Rotation in Highly-Inclined Well Section

“…Many models to calculate cuttings bed height and minimum mud rate have been established. Part of these models are theoretical, including steady models [1,2,3,4] and unsteady models [5,6,7,8], and the rest are experimental [9,10,11]. The influence rules of different factors on cuttings transport have been studied deeply except the drill pipe rotation because the pipe rotation can make the two-phase flow in annular become more complicated and difficult to solve.…”