TECHNOLOGY OF WELL TRAJECTORY CONTROL APPLYING STEM ASSEMBLY ROTATION AND ELIMINATING ROTARY CONTROLLED SYSTEMS

Abstract

The article discusses the traditional stem assembly consisting of a bit, a screw downhole motor, a telemetry system and a drilling string. This system is relatively simple, however, it has significant drawbacks which are in the non-measured zone of 15 - 20 m, and in demand of a slide mode. The slide mode has significant drawbacks: increased friction forces, which makes it difficult to transfer the load on the bit, clean the wellbore and therefore form landings during the tripping down and drill pipe drag when tripping the drill string up, and contributes to the formation of oil seals. The stem assembly consisting of: a bit, a rotary steerable system, a telemetry system and then a drilling string with a top drive has a significant advantage over the above: it illuminates the non-measured zone, which increases the accuracy of hole making, the curvature of the well is controlled with constant rotation of the drill string, which helps to improve the cuttings lifting, reducing the coefficient of friction, improving the transfer of load on the bit. The complications when wells drilling can be minimized as well. However, the stem assembly with a rotary steerable system has a high cost of operation, up to half the cost of well construction. Based on the analysis of the assemblies, a fundamentally new drill string assembly is proposed, which includes an above-bit module that excludes non-measured zone, a screw downhole motor, a telemetry system, and a top drive. The rotation of the drill string is carried out «left-right» due to the spring turned by the drill string during operation of the top drive. By adjusting the magnitude of the torque, it is possible to achieve a state where the torque decays before reaching the telemetry system and the screw downhole motor. As a result, when the drill string is rotated, the screw downhole motor can control the zenith and azimuth angles in the slide mode. Moreover, the sensors (magnetometers, accelerometers and gamma ray logging) are located in the above-bit module within the distance of 1.5 - 2.0 m from the bit.