The Effects of Mud Rheology on Annular Hole Cleaning in Directional Wells

Abstract

Summary The effects of field-measured mud rheological properties on cuttings transport in directional well drilling were studied experimentally. Water and bentonite/polymer muds were used, and angles of annulus inclination ranging from 0 to 900 from vertical. Experimental data were processed to express the cuttings transport quantitatively through annular cuttings concentration (vol%) at steady state. Three separate regions of hole inclination can be identified regarding cuttings transport: 0 to 45deg., 45 to 55deg. and 55 to 90deg. The effect of laminar flow dominates cuttings transport in low-angle wells (0 to 45deg.). In high-angle wells (55 to 90deg.), the effect of turbulent flow predominate. In the range of intermediate inclination (45 to 55deg.), turbulent and laminar flow generally have similar effects. In laminar flow, higher mud yield values and yield-point/ plastic-viscosity (YP/PV) ratio provide better cuttings transport. plastic-viscosity (YP/PV) ratio provide better cuttings transport. The effect of mud yield value is significant in the range of 0 to 45deg. hole inclination and becomes small or even negligible in the range of 55 to 90deg.. The effects of mud yield value and YP/PV ratio are more significant for lower annular fluid velocities. In turbulent flow, the cuttings transport was generally not affected by the mud rheological properties. properties. Introduction and General Discussion The problem of cuttings transport was studied by many investigators. An extensive literature review is given by Tomren. Recently, increasing attention regarding cuttings transport has been given to directional drilling. Tomren, Iyoho, and Becker, among others, have conducted studies in this area. On the basis of detailed analyses of previous and current work, several factors affect the cuttings transport in an inclined annulus. Axial and Radial Components of Particle Slip Velocity. According to gravity laws, only the axial component of the slip velocity exists in the case of a vertical annulus: ..........................................(1) This situation changes while the annulus is inclined gradually. The component of the slip velocity appears as ..........................................(2) and ..........................................(3) This situation is shown in Fig. Obviously, when the angle of inclination is increased, the axial component of the slip velocity decreases, reaching zero value at the horizontal position of the annulus. At the same time, the radial component reaches a maximum in the position mentioned. By taking these conditions into account, one can say that all factors that may lead to improved cuttings transport by a reduction of the particle slip velocity will have a diminishing effect while particle slip velocity will have a diminishing effect while the angle of inclination is increased. Annular Mud Velocity. The annular mud velocity in vertical drilling has to be sufficient to avoid cuttings settling and to transport these cuttings to the surface in reasonable time. As discussed earlier, in the case of an inclined annulus, the axial component of particle slip velocity plays a less important role, and one could conclude that to have a satisfactory transport, the annular mud velocity in this case may be lower than in the vertical annulus. The, however, would be a misleading conclusion. The increasing radial component of particle slip velocity pushes the particle toward the lower wall of the annulus, causing a particle toward the lower wall of the annulus, causing a cuttings (particle) bed to form. Consequently, the annular mud velocity has to be sufficient to avoid (or at least to limit) the bed formation. Studies show that to limit cuttings bed formation, the annular mud velocity in directional drilling has to be generally higher than in vertical drilling. Flow Regime and Regime of Particle Slippage. When the cuttings-transport phenomenon is considered, the regime of flowing mud and vertical slippage should be considered simultaneously. A mud in turbulent flow always induces turbulent regime of particle slippage, independent of the cuttings shape and dimensions. Therefore, in this case, the only factor that determines the particle slip velocity is the momentum forces of the mud; there is no influence of mud viscosity. P. 297

Impact of drilling fluid viscosity, velocity and hole inclination on cuttings transport in horizontal and highly deviated wells

“…3a-d. As far as cuttings transport in highly deviated wells is concerned, researchers offer various ideas about the effect of viscosity on hole cleaning. Some researchers such as Zeidler (1972), Okrajni and Azar (1986), Pilehvari et al (1999), Jawad (2002), Kelessidis et al (2007) and Mohammadsalehi and Malekzadeh (2011) believe that raising viscosity of the drilling fluid deteriorates hole cleaning, because type of flow regime changes from turbulent flow to laminar flow; and it has been proved that cuttings can be better displaced in turbulent flow than laminar flow. On the other hand, there are also some investigators, for instance, Ford et al (1990), Iyoho and Takahashi (1993), Belavadi and Chukwu (1994), Shou (1999), Li et al (2004) who claim that improvement in hole cleaning occurs as viscosity increases.…”

“…All lines give an upward trend by diverging from vertical, indicating that CTP has improved. Some researchers such as Okrajni and Azar (1986), Ford et al (1990), and Bilgesu and Chukwu (2007), believed that if hole angle increases, their negative influences on cutting transports will increase as well. However, the author believes that it also has some positive effects especially when the flow is laminar.…”

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 both muds with same rheological properties, water base mud has a better performance in the wells with 40°-50° inclination. Okrajni and Azar (1986) examined the effect of mud rheology on the annulus cleaning. The result of their experiments showed that mud rheology properties have a low effect on the cutting transport in turbulence flow, and in laminar flow, cutting transport is done better by increasing mud yield point.…”

“…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.…”