Songxiong Ding

Effect of Passive Inserts on the Granular Flow from Silos Using Numerical Solutions

Experimental investigations indicate that placing a passive insert in a silo is a method for influencing the discharging flow pattern. These inserts have consisted of an inverted cone, a cone-in-cone, and a double cone. However, providing unequivocal guidelines on where those inserts should be placed for an optimum effect has not been possible experimentally. A numerical approach was therefore developed to predict material flow in the presence of such inserts in silos. Simulation results showed that all these inserts could make a funnel-flow silo perform in mass flow under certain circumstances if positioned correctly. The inserts should be installed at higher levels close to the transition rather than at lower positions close to the outlet, especially with the cone-in-cone insert and the inverted inserts; the maximum diameter of the inverted cone and the double cone should, however, be below the transition of the silo. Among the three inserts investigated, the double cone appeared to be the best, although even with this insert mass flow could not always be obtained if the hopper had an inclination angle as large as 45°. In such a situation, more simulations revealed that the extension of the lower part of the double cone had the potential to improve the flow pattern in the hopper. This potential could be utilized by a combination of extending the lower cone of the double cone insert and reducing the friction between the material and the hopper wall. To ensure improvement, further simulations illustrated that a ratio of 2:7 between the maximum diameter of the insert and the diameter of the silo was also crucial for the best effect.

Experimental investigation of load exerted on a double-cone insert and effect of the insert on pressure along walls of a large-scale axisymmetrical silo

Applications of flow aid devices such as inserts improve the silo discharging mode. Considerable effort has been made in finding the best configurations between inserts and silos to achieve optimal functional results. In the present investigation, experiments were carried out to measure the loads imposed on a double-cone insert by particulate solids (free-flowing sand) when it was fitted within an axisymmetrical large-scale silo. Concentric filling/discharging was implemented to carry out such measurements. Pressures along the walls of the silo were also measured. Analyses of the measurement results showed that: (1) the loads on the insert were rather stable in total, but appeared to be asymmetrical at the end of filling; (2) a sudden increase of the loads on the insert was observed at the transition from filling to discharging, but this increase lasted only for a short moment; and (3) the loads on the insert decreased slowly but remained rather high for a large part of the discharge. Effects of the double-cone insert on the pressures along the silo walls were discussed.

Experimental Investigation of the Magnetic Shielding Effect of Mineral Powders in a Drilling Fluid

Magnetic contamination of the drilling fluid shields the Earths magnetic field measured by the magnetic sensors, and may contribute significantly to errors in directional surveying of a wellbore. A series of laboratory measurements were performed to investigate such magnetic shielding effects. In the measurement, a single axis fluxgate magnetometer was immersed in model drilling fluids prepared by mixing powders of known magnetic properties (magnetite and pure iron) into a solution of xanthan gum in fresh water, whereafter the vertical component of the Earths field inside the fluid was measured. It was found that the strong shielding effect of dry iron powder essentially vanished when was suspended in the drilling fluid. The magnetic shielding caused by magnetite, however, remained significant also in solution, showing a complex dynamical behaviour. Initially the magnetic field was significantly damped, and this shielding was found to increase further for the next hour or so, reaching a fairly sharp maximum. The shielding then started to decay slowly and irregularly again over the next few days.

The Shielding Effect of Drilling Fluids on MWD Downhole Compasses: The Effect of Drilling Fluid Composition, Contaminants and Rheology

Materials such as added clays, weight materials, drill solids and metalic wear products in the drilling fluid are known to distort the geomagnetic field at the location of the Measurement While Drilling (MWD) tool magnetometers that are used to measure the direction of well path. This distortion contributes to substantial errors in determination of azimuth while drilling deviated wells. These errors may result in missing the target of a long deviated 12 ¼″ section in the range of 1–200m; representing a significant cost to be mitigated. The error becomes even more pronounced if drilling occurs in arctic regions close to the magnetic North Pole (or South Pole). The effect on the magnetometer readings is obviously linked to the kinds and amounts of magnetic materials in the drilling fluid. The problem has recently been studied by laboratory experiments and analyses of downhole survey data.A series of experiments has been carried out to understand how some drilling fluid additives relate to the magnetic distortion. Experiments with free iron ions show that presence of iron ions does not contribute to magnetic distortion; while experiments with bentonite-based fluids show a strong effect of bentonite on magnetic shielding. Albeit earlier measurements showing a strong dependency of the content of organophilic clay, clean laboratory prepared oil-based drilling fluids show no increased shielding when adding organophilic hectorite clays. The anticipated difference between these two cases is outlined in the paper. When eroded steel from an offshore drilling site is added into the oil-based drilling fluid, it is found that these swarf and steel fines significantly increase the magnetic shielding of the drilling fluid. The paper outlines how the drilling direction may be distorted by the presence of these additives and contaminants and how this relates to the rheological properties of the drilling fluid.Copyright