Date of publication: 2017-07-09 11:20
Roegiers, . and Detournay, E. 6988. Consideration on Failure Initiation in Inclined Boreholes. Proc. , 79th US Symposium on Rock Mechanics, University of Minnesota, 966-969.
A critical foam velocity correlation has been proposed to predict the minimum foam flow rate required to remove or prevent the formation of stationary cuttings beds on the low-side of highly deviated and horizontal wells (Li and Kuru  ). The effects of key drilling parameters (. drilling rate, annular geometry, foam quality, bottomhole pressure and temperature) on the critical foam velocity were investigated.
Prof Matthew Barnett, Prof Peter Hodgson, Dr Daniel Fabijanic, Prof Svetha Venkatesh, Prof Xinhua Wu, RMIT Ma Qian, Prof B Murty, A/Prof . Janaki Ram, Prof Satyam Suwas, Dr Anand Krishnamurthy
Foams can have extremely high viscosity. In all instances, their viscosity is greater than the viscosities of either the liquid or the gas that they contain (GRI  ). At the same time, foam densities are much lower than the density of water. Foams are stable at high temperatures and pressures. So, by using foam as a drilling fluid, its high viscosity allows efficient cuttings transport and its low density allows underbalanced conditions to be established thus formation damage is minimized. Foams are also preferred when water influx is a problem because they can handle large amounts of water.
Prof Peter Hodgson, Dr Matthias Weiss, A/Prof Bernard Rolfe, Prof Jeong-Whan Yoon, A/Prof Nicole Stanford, Dr Shankar Kalyanasundaram, Dr Paul Compston, Prof Liangchi Zhang, A/Prof Zheng Jiang, Dr Dongbin Wei, Dr Matthew Dargusch, Dr Gui Wang, Dr Daniel Liang
The value calculated using Eq. 75 is the minimum acceptable mixture velocity required for a cuttings concentration, c. Pigott  recommended that the concentration of suspended cuttings be a value less than 5%. With this limit ( c = ), Eq. 75 becomes
C D is the drag coefficient of a sphere, τ y is the yield stress of the mud, and μ a is the apparent viscosity of the mud at a shear rate resulting from the settling cutting.
where f is an empirically determined friction factor. The friction factor is a function of the particle Reynolds number and the shape of the particle given by Ψ, the sphericity. Table 6 gives the sphericity of various particle shapes.
Morita, N. and Gray, . 6985. A Constitutive Equation for Nonlinear Stress-Strain Curves in Rocks and Its Application to Stress Analysis Around a Borehole During Drilling. Presented at the SPE Annual Technical Conference and Exhibition, Dallas, Texas, 76-79 September. SPE-9878-MS. http:////9878-MS.
In the more stringent limit 7 ( x558bc s x57587 / x558bc a ) k 5 7 F x558c9 x5776a 6 , the electric field autocorrelation function in Eq. () is approximately exponential:
Since the early 6985s, cuttings transport studies have focused on inclined wellbores, and an extensive body of literature on both experimental and modeling work has developed. Experimental work on cuttings transport in inclined wellbores has been conducted using flow loops at the U. of Tulsa and elsewhere. Different mechanisms, which dominate within different ranges of wellbore angle, determine:
In another study, a one-dimensional, unsteady-state, two-phase mechanistic model of cuttings transport with foam in horizontal wells was developed (Li and Kuru  ). In this model a new critical deposition velocity correlation for foam-cuttings flow is introduced. The model is solved numerically to predict cuttings bed height as a function of the drilling rate, the gas and the liquid injection rates, the rate of gas and liquid influx from the reservoir and the borehole geometry.
An experimental study of cuttings transport with foam at intermediate angles was conducted in the TU-LPAT flow loop using an anionic surfactant to determine the effects of inclination angle, foam quality, foam velocity and rate of penetration (ROP) on cuttings transport (Capo et al  ). It is shown in this study that the transport of cuttings (in terms of cuttings concentration) improves when using foams of low quality. Also, inclination and rate of penetration (ROP) have a direct impact on in-situ cuttings concentration.
Large-scale cuttings transport studies in inclined wellbores were initiated at the University of Tulsa Drilling Research Projects (TUDRP) in the 6985s with the support of major oil and service companies. A flow loop was built that consisted of a 95-ft length of 5-in. transparent annular test section and the means to vary and control