1. Field of the Invention
This invention relates generally to drilling mud separation systems, and more particularly to a drilling mud separation system which utilizes a moving continuous belt in the form of a screen, chain, self-cleaning chain link belt, or combination chain link belt and wire mesh screen to remove large drill solids and gumbo from the drilling mud or drilling fluid prior to the drilling fluid or drilling mud flowing to conventional solids control equipment.
2. Brief Description of the Prior Art
Effective solids control systems for controlling the solids in drilling mud has been a goal in the oilfield industry for many years. Various have been employed to give higher penetration rates, less contamination of formations, lower mud costs, and less abrasives and sticky materials in the mud system. The systems which are most effective require expensive and complicated machinery and require personnel to monitor and maintain the machinery. Common apparatus used for mechanically removing solids from drilling mud include shale shakers and vibratory screens, desanders, desilters, mud cleaners and centrifuges. Each piece of equipment is limited to a range of various particle sizes and selectively reject undesirable solids and retain desirable solids in the drilling fluid.
The shale shakers and mud cleaners employ a vibrating screen to selectively classify particles by size differences. The desander, desilter and centrifuge are usually located downstream from the shale shakers and utilize centrifugal force and mass difference between the solids density and liquid density for solids removal.
The initial removal step in most solids control systems is to conduct the drilling mud from the well directly to a shale shaker. Vibrating screen shale shakers of the type used in the oil industry fall into three general categories, as described below.
"Elliptical motion", or "unbalanced design" shakers have a downward slope on the screen to transport cuttings across the screen and off the discharge end. Optimum screening with these types of shakers is usually in the range of 30-40 mesh (400-600 microns), and they are prone to bearing failure.
"Circular motion", or "balanced design" shakers produce a balanced, or generally circular motion. The consistent, circular vibration allows solids transport with the basket in a flat, horizontal orientation. This type of shaker usually has multiple decks to split the solids load and allow the use of finer mesh screens in the range of 80-100 mesh (150-180 microns).
"Linear motion", or "straight-line motion" shakers produce a generally straight motion. This motion is developed by a pair of eccentric shafts rotating in opposite directions. Linear motion shakers provide superior cutting conveyance and are able to operate at uphill slope which allows the use of 200 mesh screens (77 microns).
Most prior art shakers tend to force the cuttings upward from the screen surface and as they continue upward the screen travels down, and as the cuttings fall downward, the screen travels upward and strikes the cuttings which chips small pieces off and creates very fine cuttings that are extremely difficult to remove. Shale shakers are prone to short screen life and their vibratory action tends to drive the cuttings into the screen and leads to screen "blinding" resulting in loss of fluid across the screen. "Blinding" is known as the phenomenon where near-size particles plug the screen or the screen becomes coated with sticky particles.
The present invention is not a replacement for the conventional solids control equipment but instead is installed upstream from the conventional solids control equipment and removes large amounts of large drill solids and gumbo from the drilling mud or drilling fluid prior to the drilling fluid or drill mud flowing to the conventional solids control equipment such as shale shakers. The present apparatus utilizes a separation unit removably installed in a box-like housing which receives the drilling mud or drilling fluid from the well separates the large drill solids and gumbo by utilizing a moving continuous belt in the form of a screen, chain, self-cleaning chain link belt, or combination chain link belt and wire mesh screen which moves in an continuous loop. By removing large drill solids and gumbo from the drilling mud or drilling fluid, the present apparatus improves the efficiency and performance and reduces the cost of operating and maintaining the conventional solids control equipment. Removably mounting the separation unit in the box-like housing allows a replacement separation unit to be easily and quickly installed so that operations may continue while the removed separation unit is repaired.