Shale Shakers Information
Shale shakers remove large solids (typically larger than 75 microns) from drilling fluid. (Drilling fluid is also known as drilling mud due to its turbid appearance.) Drilling fluids lubricate and cool the drill bit and are therefore integral to any drilling process. Because fluids are expensive to produce, shale shakers improve a rig's economy by stripping away cuttings for disposal before recycling the fluid.
Shale shakers consist of vibrating sieves or screens which use force to advance the filtered mud through to the mud tank. During operation the inclination of the screen varies proportional to the flow rate of mud.
Shale shakers are important components integral to the drilling process and represent the first phase of solids control in drilling industries such as coal cleaning, mining, and oil and gas production. They are often considered one of the most important pieces of equipment in the solids control system, as the efficiency and performance of all subsequent components depends on the cleanliness of the treated drilling fluid.
In the petroleum industry, drilling fluid is a critical component during well construction. It transports cuttings to the surface, prevents well-control issues and wellbore stability, minimizes formation damage, cools and lubricates the drillstring, and provides information about the wellbore. Transportation of drilled cuttings to the surface is by far the most basic and important function of mud. For both environmental reasons and to reduce the cost of drilling operations, drilling fluid is stripped of the drilled cuttings before the cuttings are disposed of and the drilling fluid is further processed for re-use. Shale shakers are the most important device on the rig for removing drilled solids from the mud. Without proper screening of the drilling fluid during this first mud processing step, downstream drilling fluid processing efficiencies and effectiveness are diminished.
Shale shakers are intensive vibrating devices. At the first stage of mud separation, they utilize a motor to generate vibrations. Acting as a sieve, the vibrating action pushes the drilling mud through a wire cloth screen. Drilling mud that filters through the shaker screen is moved into a mud tank for additional processing if necessary. Larger solids pass over the screen surface and are discharged for later collection and disposal.
Shale shaker construction.
Linear motion shale shakers represent the newest shaker technology and are the most common approach to solids control in the oil and gas drilling industries. They produce linear motion via a pair of eccentric shafts rotating in opposite directions. Linear motion provides superior cuttings conveyance and is able to operate at an uphill slope to provide improved liquid retention.
Balanced elliptical motion shale shakers are especially effective while drilling top-hole sections where heavy, high-volume solids are present. On a balanced elliptical shale shaker, the difference in power between the two vibrating motors results an unbalanced force. With this setup, elliptical motion shakers can effectively remove solids and eliminate larger particles in drilling fluids. The relatively moderate vibration strength of balanced elliptical shale shakers can reduce the screen consumption.
Circular motion shakers have a single vibrator shaft located at the center of mass of the shaker tray. A motor drives a concentric shaft fitted with counterweights, providing pure circular motion along the length of the vibrating tray. This feature improves solids movement off the deck compared with unbalanced elliptical designs. The circular motion transports solids along the screen reducing the loss of drilling fluid. Circular motion shale shakers are often operated as stacked units with the coarsest screens on the top deck becoming finer on the lower decks.
The American Petroleum Institute (API) states that every foot of well drilled generates about 1.2 barrels of waste drilling mud. The impact of waste on the cost and effectiveness of the drilling activities has become a major concern for drilling companies. Waste control and associated environmental hazards and liability have become a major driver for solids control equipment including shale shakers. Modern drill rigs have doubled or quadrupled the number of shale shakers used to process drilling fluid in order to maximize throughput and efficiency.
Though shale shakers overwhelmingly find use in petroleum exploration and production, other industries that require solids removal are worthy of mention. The mining industry relies on screening devices. Recently, the linear vibration and fine screening capabilities of shale shakers has become more desirable by coal and precious metal mining companies. The process industry also utilizes screening and shaker equipment in a variety of applications. Chemical, paper, sand, powder, plastic, and other plants may use a shale shaker in their process flow.