Study And Application Of Drill-string Rocking System In Long Horizontal Section Well

In recent years,the focus of oil and gas exploration and development has been extended to unconventional oil and gas resources.To control development costs,the extended reach wells and long horizontal section wells are now in widespread use.However,as the length of horizontal section increases,the issue of excessive drag/torque of drill-string becomes more and more prominent,especially for sliding drilling mode.The excessive drag/torque can result in serious backing pressure effect,which makes the effective weight-on-bit(WOB)and torque imposed on bit decrease obviously and then reduce the rate of penetration(ROP).This affects the drilling efficiency of the horizontal section,and even restricts its security extension.Based on lots of review and analysis of drag/torque reduction technologies both home and abroad,the investigation on drill-string rocking drilling technology was conducted.The main research achievements are as follows:(1)The conventional drag/torque prediction models for horizontal well are summarized.The calculated drag/torque results using the rigid string and soft string models under rotary drilling and sliding drilling modes are analyzed in which the drill-string buckling is taken into account.The friction coefficient of different borehole sections are inverted and analyzed to optimize bottom hole assembly(BHA)and drilling parameters.It also provides reference for torsion analysis of drill-string under rocking drilling condition.(2)Considering the characteristics of sliding friction between drill-string and borehole,the drag reduction mechanism of drill-string under rotary situation is analyzed.On this basis,the influence of reverse torque transmission of upper drill-string and positive displacement motor(PDM)on WOB during drill-string rocking is analyzed.A program for predicting the mechanical responses of drill-string during rocking drilling is developed,which contains data management,drill-string mechanics analysis and real-time monitoring of drill-string rocking modules.It can provide assistance and analysis for the optimization and determination of control parameters of drill-string rocking drilling system.(3)The drill-string rocking drilling system is developed according to the principle of intelligent slave station.It is mainly composed of top drive controller,touch operation screen,control signal switching part and fast connecting cable.It can be compatible with the top drive system to control drill-string rocking.The functions of the prototype,including torque control and loading,system zeroing and others,are tested in detail and meets the design requirements.The result indicates that the relative error between the setting torque and actual torque is less than 10%.(4)Field tests of the drill-string rocking drilling system were carried out in Sichuan and Chongqing areas.The results show that the backing pressure phenomenon can be effectively alleviated after using drill-string rocking drilling system.The transmission of WOB becomes stable,the sliding drilling efficiency is higher than 80%,the ROP increases by more than 50%,and the fluctuation range of the tool surface is controlled within plus or minus 20°.The string rocking drilling technology provides technical support for relieving the backing pressure of sliding drilling in extended reach horizontal wells.