Experimental Study of Cuttings Transport in Directional Wells

Abstract

Summary A large-scale study of cuttings transport in directional wells is discussed in this paper. Previous investigators used unrealistically high fluid velocities and/or short test sections where steady-state conditions had not been established. This study used a 40-ft [12.2-m] test section. Pipe rotation and eccentricity, as well as several types of drilling muds and flow regimes, were studied. Annulus angles varied from 0 to 90°, and actual drilled cuttings were used. The major factors affecting cuttings transport are drilling fluid velocity, hole inclination, and fluid rheological properties. Much higher annular velocities are required for effective hole cleaning in directional wells than in vertical wells. An increase in hole angle and/or drilling rate reduces the transport performance of drilling fluids. Hole angles of 40 to 50° are critical because of cuttings buildup and downward sliding of the bed of cuttings. High-viscosity muds were observed to provide better transport than low-viscosity muds. Introduction Since the introduction of rotary drilling, the circulation of drilling fluid has become an integral part of the drilling operation. Two primary functions of a circulating drilling fluid are (1) to remove generated cuttings from the bottomhole and bit teeth and (2) to lift those cuttings to the surface through the annular space between the drillpipe and the hole wall. The ability of the fluid to lift such cuttings is generally referred to as the carrying capacity of the drilling fluid. This study resulted from the need for accurate and realistic data to facilitate the optimum design of drilling-fluid systems for directional drilling. For vertical or near-vertical drilling, the problem appears to have been adequately contained. In directional well drilling, however, the inclined (usually eccentric) annulus poses several problems not encountered in vertical wells. Previous investigators1–7 have listed the most relevant factors affecting the carrying capacity of drilling fluids:fluid annular velocity;hole inclination;drilling fluid properties;penetration rate;pipe/hole eccentricity;hole geometry;annular velocity profile;particle density; settling velocity, size, and geometry;drillpipe rotary speed; andpipe/hole diameter ratio. It is difficult and impractical to investigate the effects of all these parameters simultaneously. Consequently, our objective was to develop field-oriented cuttings-transport models that account for the most significant factors affecting particle and fluid dynamics in directionally drilled wells. To achieve this objective, a two-pronged approach was adopted. Design and construct an apparatus for experimental investigation of the behavior of actual rock cuttings at realistic fluid velocities, hole inclination angles, pipe/hole eccentricities, drillpipe rotary speeds, and other relevant variables. Apply all theoretical considerations for the development of applicable mathematical relations based on detail analyses of relevant principles. These principles should include the dynamics of irregularly shaped particles in non-Newtonian fluids; the axial-velocity profile in inclined, eccentric annuli; and the tangential velocity produced by drillpipe rotation and pipe/hole eccentricity. This paper covers only the first phase of this study with brief comments on the second phase. The cuttings transport in vertical wells has been covered extensively by many investigators.1–5,8–24 In contrast, very little has been contributed to the problem of directional well drilling. Fujii and Sato25 conducted laboratory experiments at 0, 45, and 60° angles from the vertical with water and carboxymethyl-cellulose-polymer solutions and a 1.33-in. [34-mm] pipe inside a 2.36-in. [60-mm] casing. In our opinion, their results are of little practical significance because of the high, unrealistic velocities used (up to 10 ft/sec [3 m/s]) and because the short test section (10 ft [3 m]) did not establish steady-state conditions. Movsumov et al.26 attempted to solve the problem of drilled-cuttings transport in inclined, eccentric annuli purely from theoretical considerations. Their mathematical approach involved extensive trial and error and, therefore, is of little practical value, especially because their analysis was idealized to exclude the important phenomenon of bed formation that is discussed later. In the current work,6,7 a unique experimental facility was designed to provide flexibility for a comprehensive investigation of steady-state cuttings transport. Several angles of inclination, drillpipe rotations, pipe/hole eccentricities, and mud flow rates were investigated.

Improving the Cuttings Transport Performance of Water-based Mud Through the Use of Polypropylene Beads

“…This was inferred to have caused by a high impact of gravity acting on the sliding bed which led to the increase in cuttings concentrations on the lower end of the annulus. At this juncture, it is pertinent to say that this research work has demonstrated credence and the observed critical angle at 60° is in consonant with that observed by Binzanti et al (2003), Brown et al (1989), Ford et al (1990), Ogunride & Dosunmu (2012), Ozbayoglu et al (2008), , Sifferman & Becker (1992) and Tomren et al (1986). Dramatically, the declining performance of the transporting fluid reversed gradually as the hole inclination angle was changed from the near horizontal to the horizontal plane (75°-90°).…”

“…Parameters such as annular flow rate, rate of penetration, fluid density, effective fluid viscosity, cuttings size, cuttings density, well inclination and pipe/hole eccentricity play leading roles in cuttings transport performance of drilling fluid (Ozbayoglu et al 2004;Stan & Avram 2014). In the same vein, other factors such as fluid flow regime and pipe rotation have also been observed to have a great impact on drilled cuttings transport in vertical, deviated, and horizontal wellbores Ozbayoglu et al 2008;Rooki et al 2014;Tomren et al 1986). …”

Numerical modeling and simulation of drilling cutting transport in horizontal wells

“…Some of affective parameters on wellbore cleaning have been studied by some researchers experimentally (Tomren et al 1986;Yu et al 2004;Ford et al 1990;Hareland et al 1993;Okrajni and Azar 1986;Sifferman and Becker 1992;Hussaini and Azar 1983) and by modeling approach (Nguyen and Rahman 1998;Wazed 2002;Akhshik et al 2015;Zhu et al 2013). Tomren et al (1986) published the results of experimental studies with various drilling fluids in plastic pipe lines with inclination angle from 0° to 90°. They stated that for a constant mud flow rate cutting bed thickness increased by increasing inclination angle.…”

“…Although various affecting parameters on hole cleaning have been reported by some researchers during past decades (Tomren et al 1986;Yu et al 2004;Ford et al 1990;Hareland et al 1993;Okrajni and Azar 1986;Sifferman and Becker 1992;Hussaini and Azar 1983;Nguyen and Rahman 1998;Wazed 2002;Akhshik et al 2015;Zhu et al 2013), a comprehensive investigation of drilling fluid, cutting density, deposit ratio, string stress on the hole cleaning especially in horizontal wells has not been fully studied. Highlighting the contribution of the article, in this study various affecting parameters on hole cleaning in horizontal well by CFD simulator have been investigated and the results are verified with experimental data in literature.…”

PDC Bit Hydraulic & Mud Rheological simulation to model pressure drop across Bit

“…This brings about effective cuttings removal as the cuttings are removed as fast as they are generated [4]. Flow rate of mud has significant positive effect on cuttings removal away from PDC bit [5][6][7][8][9]. Increasing the annular velocity by increasing the flow rate decreases the cuttings bed height significantly.…”