体积压裂多分支裂缝支撑剂运移规律

Proppant transport law in multi-branched fractures induced by volume fracturing

为进一步明确体积压裂多分支裂缝内支撑剂的运移铺置规律,开展了不同裂缝形态、砂比、分支缝开启时机和不同粒径支撑剂注入顺序条件下的支撑剂运移模拟实验。研究表明,不同位置分支缝的逐级分流使分支后主缝砂堤高度增加,铺置长度减小。分支缝的流量是影响其充填的主要因素,分流作用使得远井分支缝流量小、充填情况较差。倾斜裂缝壁面对支撑剂施加减缓其沉降的摩擦力,提高支撑剂在裂缝纵向的分布。砂比增加可改善近井主缝和远井分支缝的充填并使主缝砂堤长度增加,由于缝高的限制,砂比提高到一定值后裂缝充填情况改善幅度减小。分支缝常开(持续扩展)时分支缝最终的支撑效果最好,但主缝铺置长度短,先关后开(后期扩展)的支撑效果优于先开后关(前期扩展)。不同粒径支撑剂顺序注入可增加主缝和分支缝的铺置长度,先小后大注入可改善近井裂缝充填,先大后小注入时近井裂缝充填情况不如先小后大注入时。

To further clarify the proppant transport and placement law in multi-branched fractures induced by volume fracturing,proppant transport simulation experiments were performed with different fracture shapes,sand ratios branched fracture opening time and injection sequence of proppants in varied particle sizes.The results show that the settled proppant height increases and the placement length decreases in main fractures as the fracturing fluid diverts gradually to the branched fractures at different positions.The flow rate in branched fractures is the main factor affecting their filling.The diverion to branched fractures leads to low flow rate and poor filling of far-wellbore branched fractures.The inclined fracture wall exerts a frictional force on the proppant to slow its settlement,thus enhancing the vertical proppant distribution in the fracture.The increase of sand ratio can improve the filling of near-wellbore main fracture and far-wellbore branched fracture and also increase the settled proppant height in main fracture.Due to the limitation of fracture height,when the sand ratio increases to a certain level,the increment of fracture filling decreases.In branched fracture,the support effect is the best when it is always open(or extends continuously).In main fracture,where the proppant placement length is small,the support effect is better when it is first closed and then opened(or extends in late stage)than when it is first opened and then closed(or extends in early stage).Injection sequence of proppants in varied particle sizes can improve the placement lengths of main fracture and branched fracture.Injection of proppants in an ascending order of particle size improves the near-wellbore fracture filling,to a better extent than that in a descending order of particle size.