Method and apparatus for monitoring of downhole dynamic drag and torque of drill-string in horizontal wells

Monitoring and control downhole drag and torque is a eternal research topic in horizontal drilling technique, but the theory and experience are still in the exploring stage. In this work, an integrated dynamic monitoring method, including a downhole parameters measuring system and a model for calculating the effective weight of drill-string, is proposed to discover the downhole drag and torque. A computational program is developed in the Visual Basic environment. Taking well T2-4-22H1 as an example, the downhole experiment are conducted to obtain downhole weight-on-bit (DWOB) and downhole torque-on-bit (DTOB) by using the developed downhole parameters measuring apparatus (DPMA). The experiment results are utilized for verifying the feasibility and suitability of the present method. The results show that the measured DWOB is significantly lower than the recorded surface weight-on-bit (SWOB) under sliding mode. As a result, the downhole based drag force is obviously higher than that based on surface data. For rotary mode, though the weight-on-bit and drag force do not make significant difference on both surface and downhole, but excessive frictional torque is generated due to drill-string rotating. The main reasons caused the diversity of surface and downhole parameters are discussed. Additionally, based on the measured downhole parameters, the changing rules of friction coefficient under different drilling modes are inversed. The present drag and torque monitoring method can provide a powerful technical support for the safe and high-efficiency drilling of horizontal wells.