基于大位移井井眼清洁与钻柱力学动态耦合模型的钻井参数优化OA

With the development of unconventional oil and gas resources and offshore oil and gas,extended-reach well has gradually become an important well type.The cuttings accumulation in extended-reach wells has adverse impact on drilling efficiency and even threatens downhole safety.However,there is no quantitative coupling method for analyzing the influence of cuttings beds on drillstring drag and torque.In this paper,the quantitative coupling relationship of cuttings bed height with drag and torque is established on the basis of laboratory experimental results,and then integrated with transient cuttings transport model and friction-torque calculation model to form a transient hole cleaning-drillstring mechanics coupling model.This model enables the dynamic simulation of cuttings distribution and drillstring stress in wellbores and their evolution under varying drilling conditions.The following results are obtained.First,compared with the models only considering steady-state cuttings transport,the proposed coupling model provides a more accurate description about the drillstring mechanical response under the conditions of dynamic cuttings accumulation,and is more applicable to complex working conditions in extended-reach wells.Second,when cuttings bed thickness increases from 0 to about 80 mm(cuttings volume fraction is about 23%),the drillstring frictional torque increases by 30%-50%,and the axial drag increases significantly,leading to a significant reduction in effective weight on bit and a great increase in drillstring buckling and sticking risks.Third,off-bottom circulation time is a key parameter governing the formation and development of cuttings beds.An optimization method with off-bottom circulation time minimization as the objective is established by introducing circulation time constraints into the two-dimensional parameter domain.This method takes the continuous drilling of 2-4 drillstrings as the optimal operating interval on the premise of satisfying Equivalent Circulating Density,safety torque and drillstring buckling constraints.In conclusion,the proposed coupling model provides the synchronous dynamic description about the cuttings distribution and stress under the alternative working conditions of drilling and circulation,and the established transient hole cleaning and drillstring mechanics collaborative analysis method provides a theoretical basis for drilling parameter design and safety control of extended-reach wells.