New Developments in Aerated Mud Hydraulics for Drilling in Inclined Wells
- A.A. Sunthankar (U. of Tulsa) | E. Kuru (U. of Tulsa) | S. Miska (U. of Tulsa) | A. Kamp (INTEVEP)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- June 2003
- Document Type
- Journal Paper
- 152 - 158
- 2003. Society of Petroleum Engineers
- 1.11 Drilling Fluids and Materials, 1.8 Formation Damage, 4.1.5 Processing Equipment, 5.1.1 Exploration, Development, Structural Geology, 1.6.3 Drilling Optimisation, 4.1.2 Separation and Treating, 1.7.1 Underbalanced Drilling, 1.10 Drilling Equipment, 5.3.2 Multiphase Flow, 4.2 Pipelines, Flowlines and Risers, 4.3.4 Scale, 1.7.7 Cuttings Transport, 1.7.6 Wellbore Pressure Management, 1.6 Drilling Operations, 1.7.5 Well Control, 2.1.7 Deepwater Completions Design, 4.1.6 Compressors, Engines and Turbines
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An experimental study of aerated mud flow in an inclined well has been conducted, and the results are presented in this paper. Extensive experiments were performed in a unique field-scale low-pressure flow loop (8×4.5 in. annular geometry and 90 ft long) in an inclined position (15° from vertical) with and without drillpipe rotation. Water and an aqueous polymer solution [CMC (sodium carboxymethyl cellulose)+XCD (xanthan gum)+water] were used as the liquid phase. The liquid flow rate was in the range of 100 to 325 gal/min. The air flow rate was in the range of 8 to 85 scf/min. Measurements of pressure drop and average liquid holdup were carried out for the entire annular section. To our knowledge, no such data has been published previously.
The two-phase flow patterns were identified by visual observations. Bubbly and slug/churn (intermittent) flow were observed for the ranges in the chosen test matrix.
The flow-pattern boundaries proved to be shifted as compared to pipe flow. The transition between bubbly and slug flow was observed at a void fraction of 0.32 as compared to that reported for pipe flow (0.25) for air-water flow. On the contrary, for air-aqueous polymer fluid, flow was the same as for air-water pipe flow (0.25). For flow with drillpipe rotation, churn flow was observed instead of slug flow because of the churning of slugs by the rotating drillpipe.
There was no significant effect of drillpipe rotation on the pressure drop for air-water flow. However, in the case of air-aqueous polymer fluid flow, the pressure drop decreased with drillpipe rotation.
A higher pressure drop was observed in case of air-aqueous polymer fluid flow as compared to air-water flow.
The aerated drilling fluids have the major advantage of controlling mud effective density, which influences the borehole pressure. Therefore, the aerated muds can be used to explore and exploit low-pressure reservoirs and to meet the requirements of underbalanced and/or balanced drilling. Aerated muds have the potential to increase the rate of penetration, minimize formation damage and lost circulation, and reduce drillpipe sticking, therefore assisting in improving productivity.1 Recently, the technology of drilling with aerated muds has reached even the area of offshore drilling.2,3
Because of the complex flow mechanisms involved in aerated drilling-fluid flow, predicting bottomhole pressure as a function of the gas and liquid injection rates becomes very difficult. This results in a lack of confidence in controlling the operational variables, such as gas-liquid injection rates, and in predicting variables like bottomhole pressures.
There have been only a few studies conducted on two-phase flow in annuli. Most of the available literature is concerned with the study of two-phase flow in small-scale vertical and inclined annuli that does not represent typical wellbore geometry used for drilling applications. Sadatomi et al,.4 Kelessidis and Dukler,5 Caetano et al.,6 and Das et al.7 reported experimental investigations leading to the development of flow pattern maps for two-phase flow in vertical annuli. Kelessidis and Dukler,8 Hasan and Kabir,9 and Hasan et al.10 combined the experimental study with hydrodynamic modeling to investigate two-phase flow characteristics. Mechanistic models of various flow patterns observed in upward two-phase flow in annuli were presented by Kelessidis and Dukler,5 Caetano et al.,11 Das et al.,12 and recently by Lage and Time.13 The literature also reveals few studies related to two-phase flow in large-scale vertical and inclined annuli. Nakagawa and Bourgoyne,14,15 Johnson and White,16 and Johnson and Cooper17 reported their investigations in large-scale annuli; however, their studies were mostly related to the gas migration velocities encountered during gas kick in vertical and inclined annuli. Shiomi et al.18 investigated the effect of pipe rotation on two-phase flow patterns in a concentric annulus with a narrow annular gap.
Recently, a comprehensive study of aerated mud flow in horizontal and inclined wells was conducted.19 Results from this study regarding the flow of aerated muds in horizontal wells have been presented previously by Sunthankar et al.20 The results from the second part of this study regarding the flow of aerated muds in inclined wells are presented in this paper.
The following sections present details of the experimental study carried out to investigate the two-phase air-water and air-aqueous polymer solution flow in large-scale annulus in inclined position with/without drillpipe rotation.
Experiments were conducted in the unique experimental facility available at the U. of Tulsa (Fig. 1). A schematic diagram of the experimental facility is given in Fig. 2.
The flow loop is approximately 90 ft long with an 8-in. inside diameter (ID) transparent acrylic casing along with a 4.5-in. outside diameter (OD) inner drillpipe. The inner drillpipe can be rotated at variable speeds (0 to 150 rpm). The flow loop can be inclined at any inclination, from approximately 10° (nearly vertical) to 90° (horizontal). Experiments were conducted at 15 and 45° inclination angles. Only results from the tests conducted at 15° inclination are reported here. The results from 45° inclination tests are given in detail elsewhere.19
A centrifugal pump (maximum capacity of 650 gal/min) and a compressor (with working capacity of 0 to 1,200 scf/min at a delivery pressure of 125 psi) were used to supply liquid and compressed air.
The pressure drop was measured for the full test section (76 ft of separation) and the half test section (36 ft of separation). A "quick-closing valve" technique was used to measure the average liquid holdup. The valves located at both ends of the flow loop were closed simultaneously to trap liquid inside the annulus, and the flow was diverted via a bypass line. The hydrostatic pressure exerted by the trapped liquid column was measured, and the total liquid volume trapped inside the loop was calculated accordingly.
A fixed, high-speed camera was used to record the two-phase flow through the loop. In addition to high-speed camera recordings, each test was recorded with a hand camera. The recordings were used later to confirm visual observations.
Experiments were conducted with air-water and -viscous non- Newtonian aqueous polymer solution (water+4 lb/bbl of CMC+0.3 lb/bbl of XCD) in an inclined, nearly vertical position (15° from vertical) with and without drillpipe rotation (100 rpm).
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