| In recent years, along with the exploration of unconventional oil gas resources and the high efficient development of "three-low" oilfields, extended reach wells and horizontal wells with long horizontal wellbores have been in wide use. Along with the increase of the length of the horizontal wellbore, the friction and torque of strings increase severely, which is apt to cause backing pressure. Especially in the process of sliding drilling, owing to the un-rotation of string, which easily leads to the uncleanness of the wellbore, the friction of the integrate string system increases, resulting in serious backing pressure, eventually influencing the rate of penetration of the horizontal wellbore.Based on the application of the downhole engineering parameter measuring instrument in Sulige Gas field, the ways of dynamic friction and torque measurement and dynamic friction and torque index inversion have been proposed in this paper. Based on the theories of drill-string mechanics, the finite element simulation, and field experiment, the measurement and research of friction and torque of strings in long horizontal wellbores have been carried out, attaining several results, lying as follows:A downhole engineering parameter measuring instrument has been designed to be applied in experiment well. This instrument conducts measurement by way of strain testing principle. Through the general structure design, optimization design, the finite element simulation and calculation, laboratory experiments, a downhole engineering parameter measuring instrument has been manufactured to be applied in Sulige Gas field, and the performance indicators meet the field measurement conditions.A field experimentation has been conducted in well tiao2-4-22H1, nearly30hours’ measurement data were collected, including data of trip in different depth, surficial WOB and downhole WOB, surficial torque and downhole torque, all logging data in corresponding period and wellhole trajectory data, which laying the foundation for the frictional analysis.Based on the measured data, the basic thinking of dynamic friction measurement in horizontal well has been proposed, the measuring principle has been studied; the calculation model of string’s effective weight in different sections has been deduced. Obtained the dynamic friction of tiao2-4-22H1by the application of the dynamic friction access method in horizontal well.The drill string’s force in the experiment well has been analyzed, compared the theoretical friction in different working conditions obtaining by three dimensional calculating model for the friction with dynamic friction measurement results. The results show that, surficial WOB and downhole WOB have vast difference during sliding drilling and the dynamic friction measurement results are larger, which indicate there existing severe backing pressure. In the process of rotary drilling, surficial WOB and downhole WOB have smaller difference, backing pressure phenomenon is not obvious. Sliding drilling accounts for a long time, and the rotary drilling efficiency is low, resulting in slow penetration. Based the existing problems during the dynamic friction measurement in horizontal well drilling of sulige Gas field, the inversion method of dynamic friction index in different working conditions has been proposed to find its change rule in the drilling process, to carry out the optimization research of horizontal drilling in experimental block. Eventually, obtained the recommended optimization measures for horizontal section drilling according to analyze conclusion and the change rule. Then applied these measures to the similar well, greatly improved the rate of penetration and the overall efficiency of drilling, which proved the feasibility of optimization suggestions. To a certain extent, it may be useful for the drilling of the long horizontal section in horizontal wells of Sulige gas field. |
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