Calculation and Experimental Study on a Rotary Percussion Positive Displacement Motor

A positive displacement motor (PDM) driven rotary percussion drilling tool, named rotary percussion PDM (RP PDM), is developed. Using conventional PDM as rotating power source, high-frequency axial impact and vibration or impact is generated to raise rate of penetration (ROP) through an impact mechanism consisting of a couple of mating cams. Strength is calculated and checked for dangerous cross-sections, and all of them meet the strength requirements. Stress distribution under different loads is analysed for the mating cam mechanism. Safety coefficients of upper and lower cams under maximum load are 3.69 and 2.36 respectively. Both are greater than the allowable safety coefficients, which prove tool's design safety and reliability. Ground performance test shows that its overall power output parameters meet field compound drilling condition requirements. Field trials shows preferable ROP improving effect by over 30%. In Xu36A well especially, ROP is more than doubled. Therefore, the tool has positive significance to accelerate the pace of oil exploration and development and to reduce drilling costs.