中文摘要：

复杂裂缝内的支撑剂输送是压裂现场急需改善的关键问题之一,通过提高支撑剂在分支缝内的充填效率,能够显著提高油气增产效果.目前,复杂裂缝内的支撑剂输送研究还处于室内实验探索阶段,鲜有成熟的理论研究报道.本文总结了国内外最新研究进展,提出压裂液分流量和支撑剂转向条件是复杂裂缝携砂的两个关键参数,并将复杂裂缝系统抽象成单元化物理模型,分别开展了分流量和转向条件研究.借鉴限流压裂中压裂液分流量的计算方法和建模思路,分别建立了复杂裂缝单元模型中的压裂液分流量算法和改进算法,采用Fluent进行了分流量模拟和对比验证,结果表明,改进的算法与Fluent模拟结果相对误差为-2.76%,计算结果较准确.提出由砂堤表层支撑剂起动的临界流速表征支撑剂向分支缝转向输送的临界条件,并给出了临界转向条件的算法,将算法的计算结果与Colorado School of Mines的实验结果进行对比分析,平均误差为8.18%,表明该算法能够较好地预测支撑剂转向临界流速.综合压裂液分流量和支撑剂转向条件算法,在Katherine Thomas Technology Center的实验条件下,预测了不同粒径支撑剂在分支缝内的输送情况,结果与实验结论一致,从而为改善复杂裂缝内的支撑剂输送提供了理论和方法依据.

英文摘要：

The proppant transport in complex fracture has been a hot area of research. Via optimizing the pumping parameters, like pump rate and proppant type, the proppant packing efficiency will be improved in the branch fractures, by which the stimulation results will be enhanced. The research work on proppant transportation has just started, and the laboratory physical simulation experiments are the main methods. The researchers from Katherine Thomas Technology Center and Colorado School of Mines have carried out proppant transporting experiments in complex fractures separately. The major finding is the mechanism that the proppant flows from the main fracture turning into the branches：（1） the gravity effects of the proppant bed;（2） the fluid drag effect under the critical flow rate. However, only the descriptive results were obtained from the experiments. The further numerical models and calculations based on the experimental findings still can＇t be found in the current reports. This paper was aimed to reveal the proppant transporting in complex fractures using numerical methods. By literature surveys, the fractional flow of fracturing fluid and critical condition of proppant diversion were proposed to be the key parameters of proppant transport in complex fractures. The calculations of fluid fractional flow in complex fractures and the critical condition of proppant diversion were derived and verified in this paper. The fracture unit model was abstracted and used to describe the complex fractures, by using which the complex fractures could be simplified into the combination of superior fracture and sub-fracture. The fracture unit model was compared with the model of limited entry fracturing for the fluid flow, formation condition, flow friction, etc. A calculation of fracturing fluid fractional flow in complex fractures was built referring to the calculation of limited entry fracturing. Furthermore, an improved calculation of fracturing fluid fractional flow in complex fractures was derived based on the ele