The present invention relates to an improved vibratory screening machine and feeder combination and to an oil or gas earth drilling installation utilizing said vibratory screening machine and feeder combination.
By way of background, a drill platform for drilling for oil or gas includes a drill rig having a drill casing and a bell nipple. Drilling mud is supplied through the drill casing for lubricating the drill and carrying drilled materials back to the surface. The drilled materials carried by the drilling mud are discharged from the bell nipple. The drilled materials may include rock, shale, clay or sand or combinations thereof. The drilling mud is separated from the drilled materials in a vibratory screening machine and reused. A conventional vibratory screening machine includes a feeder which receives the outflow from the bell nipple and an angularly adjustable vibratory frame having a screen bed on which screens are mounted. The feeder discharges the material to be screened onto the screen bed. The screen bed of the vibratory screening machine must be angularly adjusted for properly screening different compositions of drilled materials. The vibratory frame is positioned above a hopper which receives the drilling mud which passes through the screen bed. The height of the hopper determines the elevation of the screen bed, and the outflow from the feeder is above the screen bed. In the conventional screening machine the vibratory frame must have a walled construction proximate the feeder in order to retain the outflow of the feeder on the screen bed. Therefore, the outflow from the feeder has to be at least a foot above the screen bed to get over the walled structure of the vibratory frame. Also, the feeder is not physically connected to the screen bed because otherwise vibrations of the vibratory frame would be transmitted thereto. Additionally the feeder is not connected to the screen bed because the screen bed must be separate from the feeder so that it can be angularly adjusted.
It is conventional to conduct the outflow of the bell nipple to the screening machine by a gravity feed, especially considering that it is impractical to pump drilled materials containing rocks and shale. In order to have the desired gravity feed from the bell nipple, to the feeder of the conventional screening machine, the conventional screening machine must therefore be placed in a lowered position on the drill platform. This may be difficult to achieve because of space and structure limitations on the drill platform. Therefore, the lower the outflow from the feeder, that is, the closer the outflow from the feeder to the screen bed, the easier it will be to have the outflow of the bell nipple higher than the outflow from the feeder without requiring specialized placements of the vibratory screening machine on a drill platform.