Calculation and analysis of dynamic drag and torque of horizontal well strings

In recent years, shale gas production horizontal well types mainly include conventional horizontal well, highly deviated well and scoop-shape horizontal well. For the sake of construction decision making, it is necessary to study these three types of wells from the aspects of drag and torque characteristic, weight on bit transferring efficiency, key hole sections or links and extreme penetration length. In this paper, these three types of horizontal wells were taken as the study objects. Their drag and torque, load transfer and extended reach drilling were explored based on the dynamic model of full hole drilling string and the simulation calculation of dynamic characteristics of full hole drilling string system. And the results were applied and tested on site in three shale gas wells (a conventional horizontal well, a highly deviated well and a scoop-shape horizontal well) in the Changning area, Sichuan Basin. And the following research results were obtained. First, the contact friction strength of the deeper part of the buildup section in the scoop-shape horizontal well is very high, and it is 1.67 times that of the hold section. The total contact force of buildup section in the scoop-shape horizontal well is 1.62 times that in the highly deviated well. Second, the contact friction strength of the hold section in highly deviated well is not only higher than that of its buildup section, but also higher than any characteristic section in the three well types of the same depth. Third, the operating stress of drilling strings during the drilling of three well types is not high, but during the extended reach drilling in the curved section of the scoop-shape horizontal well, it is necessary to focus on the twist off of drilling string in the hold section. Fourth, the weight on bit transferring efficiency of scoop-shape horizontal well is lower than that of conventional horizontal well and highly deviated well. In conclusion, the research results preliminarily reveal the drag and torque characteristics and active load transferring mechanisms of conventional horizontal well, highly deviated well and scoop-shape horizontal well for shale gas production, and present important hole sections for safety assessment. They can be used as references for efficient and safe construction of shale gas horizontal wells.