Coiled-tubing drilling (CTD), which has grown significantly in recent years, is normally associated with high-angle to horizontal and extended-reach wells. In these applications, however, hole problems become more troublesome because of inefficient cuttings removal. Among the many parameters affecting efficient cuttings transport in CTD are pump rates, well dimensions, fluid properties, solid sizes, solid loading, and hole inclination. Several attempts have been made to determine the optimum operating range of these parameters, but complete and satisfactory models have yet to be developed.The purpose of this paper is as follows:• To provide a critical review of the state-of-the-art modeling for efficient cuttings transport during CTD.• To present the critical parameters involved.• To establish their range according to what is observed in practice.• To propose a different approach for predicting the minimum suspension velocity.• To describe the laboratory system that has been set up. The primary purpose of the flow system is to enable the gathering and publication of good-quality data that, together with previously published data, could further enhance our understanding of the flow of solid/liquid mixtures in annuli.

The phenomena occurring during the flow of dilute solid-liquid mixtures in a horizontal concentric and 100% eccentric annulus are presented, analyzed and discussed. The experiments were performed in a 5 m long, 7 cm by 4 cm transparent annulus. A range of superficial liquid velocities between 0 and 2.32 m/s were studied, with water and two aqueous Carboxyl-Methyl-Cellulose (CMC) solutions; one with Newtonian rheology (with a viscosity of 6.79 cP) and one with non-Newtonian rheology (with apparent viscosity of 8.3 cP at a shear rate of 170 s−1). The solids used were 2 mm glass spheres with sphericity close to one, while the tested solid loading was 2% and 4% w/v. The flow patterns at various experimental conditions were observed visually by video monitoring equipment and were analyzed to produce flow pattern maps. The main parameters affecting the transitions to the particular flow pattern are presented and the conditions for the transition are discussed. A method is presented for flow pattern detection using pressure drop measurements and the positive implications for real-life applications are discussed. Introduction Flow of solid-liquid mixtures in conduits is encountered in several situations of industrial significance like solid transportation with long pipelines, oil well and geothermal drilling, oil and gas production and mineral and waste-water processing. The flow geometry may be pipe or annulus in a vertical, inclined or horizontal orientation. While the issues dealing with vertical configurations have been mostly resolved, there are several unresolved issues for the flow of two-phase solid-liquid mixtures in horizontal and inclined conduits(1–10). During the flow, the liquid and solid phases may distribute in a number of geometrical configurations or flow patterns. The main parameters determining a particular flow pattern are the liquid velocity, the solid loading, the physical properties of the liquid and of the solids, the inclination angle and the conduit shape and size(2, 11,12). A detailed description of the flow patterns in a concentric annulus has been given by Kelessidis and Bandelis(13). They are the suspended symmetric flow, the suspended asymmetric flow, the moving bed flow and the stationary/moving bed flow (see Figure 1). At even lower liquid superficial velocities, the solids pile up in the annulus and full blockage may occur. Experimental evidence and theoretical analysis indicate that this may occur at relatively high solids concentrations. There have been several theoretical and experimental studies of solid-liquid flow in conduits(1–10, 14, 15) to describe the phenomenon, with many covering the situations of high solids loading (>20% w/v) targeting primarily slurry transport. However, there are situations of industrial significance, like oil-well drilling, where the volumetric solids concentration rarely exceeds 5% w/v(13). Solid suspension by liquid turbulent forces has also received considerable attention(13, 16, 17). FIGURE 1: Schematic representation of flow patterns in a horizontal concentric annulus(13) (Available in full paper) Flow pattern maps for the flow of two-phase solid-liquid mixtures flowing in horizontal pipes have been presented previously(5, 10, 11) but flow pattern maps for the flow in horizontal concentric and eccentric annuli have not been presented.

The combustion behavior of selected agricultural residues (olive and peach kernels, almond and walnut shells) and their blends was investigated in a prototype low-investment combustion unit of nominal capacity 65 kW th. Blending ratio for olive kernel was 50 or 70%, while for the rest of the residues 30 or 50%. Flue gas temperatures, inlet and outlet water temperatures of the boiler and gaseous emissions were measured at specific feed and air flow rates and combustion and boiler efficiencies were determined. CO and NO x emissions from all fuels during the whole operation of the unit were below legislation limits, while SO 2 emissions were negligible. Combustion efficiencies were satisfactory, ranging between 84 and 86%. Peach kernels burned with the highest efficiency. By blending olive kernels with peach kernels, almond or walnut shells at percentages up to 50%, the overall efficiency of the system in terms of emissions and degree of combustion was improved, achieving the best performance with olive kernels/peach kernels 50:50 blend. Co-combustion of unpelletized materials could be predicted to a great extent from the combustion of component fuels, offering apart from environmental and economic benefits.

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Casing drilling can be an effective method of reducing drilling costs and minimising drilling problems but its uptake around the world has been slow with only a few wells drilled so far with casing. Complex geological features like the high overburden on top of shallow unconsolidated reservoirs characteristic of offshore West Africa can benefit from casing drilling when effectively combined with Managed Pressure Drilling technique. For the industry to develop a managed pressure drilling capability that will allow today’s generation of complex wells to be drilled safely with casing, it is necessary to develop models that include the effect of eccentricity , rotation and fluid rheology at bottom hole conditions on flow and pressure regimes, and to embed these models within an easy to use, intuitive well design package for pre planning and as a real time tool to monitor and provide forward simulations based on real time rig and downhole data. The paper presents new results of the theoretical predictions of the wellbore pressure regimes incurred when different types of drilling fluid flows in concentric and eccentric horizontal annuli. The concentric and eccentric casing drilling results are compared with parallel predictions from conventional drillstring results from developed analytical solutions integrated into the VisWELL(DeskTop Simulator) , which is used in simulating well operations.