Analysis of Cuttings Transport and Flow Pattern in Nearly Horizontal Extended Reach Well

Abstract

During the drilling activity, in an extended reach well, the deposition of cuttings (solids) in the annulus can lead to issues such as differential sticking and inefficient hole cleaning. This makes it essential to identify different multi-phase flow patterns and study the effect of drill pipe eccentricity and rotational speed on cutting transport in the annulus. Therefore, in this study, the experiments were conducted in a near-horizontal flow loop system, where the length of an annulus section was 6.16 m (20.2 ft) long and the outer and inner diameters were 4.5 in. (11.4 cm/0.37 ft) and 2.5 in. (6.4 cm/0.21 ft), respectively. A high-speed CCD camera was used to perform the in-situ visualization of the multiphase-flow through the annulus. Then the recorded videos were used to investigate the cuttings transport for both 2 and 5 wt% solid concentrations. Glass beads having a diameter of 0.5-2 mm were used as cuttings for the experiments. The video recordings were used to scrutinize the flow behavior pattern which depicts the possible flow patterns for the gas-liquid-solid multiphase-flow through horizontal annuli. The effects of varying pipe eccentricity (0 to 75 %), drill pipe rotational speed (0- 120 RPM), air pressure (0.4-0.8 bar) and solid concentration on the cuttings transport through the annulus were investigated. It was observed that high rotational speed and eccentricity of the drill pipe lead to better hole cleaning. At 30% eccentricity, the solid bed height was found to vary from 8 to 20 times at different rotational speeds for changing the solid concentration form 2 wt% to 5 wt%. Moreover, while different drilling conditions were tested for cutting transport, six distinguishable flow patterns were observed. The findings also show that 75% of eccentricity may not be optimum drilling conditions because of the contact between cutting and the drill pipe. The novelty aspect of this work was the use of three phases (solid, liquid and gas) to investigate the flow pattern behavior and cutting transport phenomena in the annular flow loop system by varying drill pipe rotational speed and drill pipe eccentricity. The flow map of this work can be used to develop 3-phase models to figure out optimum conditions for cutting transport in horizontal wells for enhanced oil recovery.