The rotary drilling equipment used for oil drilling. It is usually composed of four main operations: hoisting, rotating, circulating, and power. The rotary drilling rig is caused to rotate by means of the power plant, thus causing the solid fracturing when the bit is rotating. According to different ways of mud circulation, the rotary drilling rig can be divided into two different types: positive circulation rotary drilling rig and reverse circulation rotary drilling rig.
The drilling rig of positive circulation rotary drilling rig is driven by rotary device to cut rock and solid. Meanwhile, wash the bottom by transporting mud or clean water to drill pipe with the help of mud pump. The liquid filled with debris will rise along the annulus between drill pipe and bore, flow from orifice to sedimentation tank. The liquid can be reused after purification, and so forth. And that is what called positive circulating discharge system. While the debris is continuously discharged, the drill becomes deeper and deeper, until the expected depth. Since the discharge way is the same with the geological exploration drilling’s, we call it positive circulating.
The drill hole caused by reverse circulation rotary drilling rig is also driven by rotary device. The slurry circulate through pumping, gas lifting, injection, and so on. According to the principle of suction, it can be divided into three types: pump suction reverse circulation, air-lift reverse circulation and injection reverse circulation. The pump suction reverse circulation make the liquid up by the help with pumping action caused by gravel pump. Air-lift reverse circulation use the high velocity flow sprayed by jet pump to form negative pressure, making the liquid go up and forming reverse circulation. The injection reverse circulation make the liquid circulate by compressing air into the drill pipe. The rate of liquid rise has something to do with weight differences in and out of the pipe. The deeper the drill hole is, the more efficient it would be. When the depth is less than 50 m, we would better choose the way of pump suction reverse circulation or air-lift reverse circulation. However, when the depth is more than 50 m, the injection reverse circulation would be better.