Study On Solution Of Backing Pressure While Drilling Horizontal Well By Using Hydraulic Forcing Principle

With the great increase of production difficulty in oil-gas fields, the horizontal drilling technology is applied more and more widely. However, the special wellbore trajectory of horizontal well results in the weight on bit of horizontal section is difficult to be applied, which is called backing pressure. It seriously affects the drilling time-efficiency and drilling safety. Therefore, how to put weight on bit is the key to solve backing pressure.Two kinds of downhole hydraulic transmission tools were proposed at home and abroad to solve backing pressure. They are sliding forcing and rotary forcing respectively. The former category includes coiled tubing anti-friction device and hydraulic thruster, and the latter is hydraulic impactor. Cuttings bed can form easily in low side of horizontal section using sliding forcing, while the structural design of rotary hydraulic impactor is complex and its application cost is high. Based on previous research, this paper combines the advantages of two kinds of downhole hydraulic transmission tools—sliding forcing and rotary forcing, this paper designs a new type of rotary CZ type hydraulic thruster and based on the correlation theory of mechanical engineering, hydraulics and vibrational science. It consists of multistage pressure cylinder in series, and its exterior has rotating balls and spring is installed in last stage piston cylinder. In the process of work, the tool not only helps horizontal section cuttings rise smoothly in the form of rotation, but also absorbs vibration effect through spring and return piston, thus decreasing drill string vibration and guaranteeing stationarity of putting weight on bit.Finally, the paper researches on the vibration absorption theory of CZ type hydraulic thruster to drill and gives relational expression between CZ type hydraulic thruster and drill vibration and then solves it based on the three different levels CZ hydraulic thruster. At the same time, the longitudinal vibration of piston and the movement rule of piston rod are studied. The calculations results show that CZ type hydraulic thruster can increase exceed 10% WOB, which improves the drilling efficiency in horizontal section.