Adaptability research on compound drilling technologies to formations in western Sichuan

Field test is conducted to improve the penetration rate, reduce the drilling cost, and accelerate the exploration and development of the gas reservoir in Xujiahe formation in western Sichuan. Results show that the formation’s drilling strength in Penglaizhen formation is enhanced along with the increase of the bit load and the rotation rate. The drilling rate in Penglaizhen formation increases dramatically, while that in Suining and Shaximiao formations increases more slowly. Considering the factors such as the formation lithology and the formation pressure gradient, Suining and Penglaizhen formations are fit to drill with high rate. It is shown that the average penetration rate used in 311.15 mm and 215.9 mm wellbore of Penglaizhen and Suining formations can be increased twice higher than that used in the formations without using compound drilling. Compound drilling is not fit to be used in the Shaximiao, Qianfoya, and Xujiahe formations, because the formation pressure gradient exceeds 1.5 MPa/100m. Also compound drilling can not be used in Baitianba formation, owing that the gravels in the formation may accelerate the abrasion of PDC bit. Field tests show that when the compound drilling is applied to the the vertical and fast drilling technology, it can increase the bit load for more than 50% compared with the pendulum assembly in addition to controlling borehole deviation. As a result, the compound drilling technology suitable for the safe and faster drilling in western Sichuan is developed.