Abstract: Because the ultra-shallow horizontal well in Block Chepaizi of Xinjiang has shallowly-buried target layer, poor diagenesis, large difference in drillability, and very low and unstable angle-building rate, large-degree progressive displacement motor (PDM) is needed to control the trajectory of the angle-building section. A large-degree PDM has large torque during compound drilling, and is very likely to have screw failure, which is not conducive to safe drilling. For the drilling of horizontal section, it is necessary to trip out and replace the large-degree PDM with a small-degree one. A large-degree PDM can neither achieve trajectory control for the secondspud vertical section, the deviated section and the horizontal section in one trip nor satisfy the demand for safe drilling. The analysis shows the one-trip drilling technique for the ultra-shallow horizontal well in Block Chepaizi requires that the PDM should not only have a high angle-building rate, but also be able to reduce the torsional force produced by compound drilling, so as to prevent the screw from twisting off or breaking off. Based on this, short-bend point PDM that meets the requirements is optimized and designed, which has the distance from the bend point of a conventional one to the bottom of bit adjusted to 1.3 m from 1.8 m. After such adjustment, anglebuilding ability of the screw is basically unchanged, but the screw offset value is reduced from 0.056 m to 0.038 m, which further reduces the torsional force acting on the PDM enclosure under compound drilling conditions from 3.7 kN·m to 1.5 kN·m. The newly-designed PDM can effectively control the trajectory by way of slide drilling combined with compound drilling, and complete the directional drilling operation of the ultra-shallow horizontal well in Block Chepaizi in one trip.

Key words: ultra-shallow horizontal well, short-bend point PDM, one-trip drilling, PDM drilling tool, Block Chepaizi

摘要：

关键词: 超浅水平井, 短弯点螺杆, 一趟钻, 螺杆钻具, 车排子