选取准噶尔盆地玛湖凹陷二叠系乌尔禾组砾岩岩心开展真三轴加砂压裂实验,研究杂基支撑细砾岩、颗粒支撑中砾岩水力裂缝扩展形态与石英砂支撑剂运移情况,并通过3D打印技术对砾岩压后粗糙面进行重构,分析粗糙面对导流能力的影响。研究表明：杂基支撑细砾岩水力裂缝整体相对平直,仅局部遇较大砾石时迂曲明显,易于加砂,缝内支撑剂运移距离约占缝长的70%~90%;颗粒支撑中砾岩水力裂缝以绕砾扩展为主,路径迂曲,缝宽多变,不易加砂,缝内支撑剂运移距离不足缝长的30%。杂基支撑细砾岩因基质含量高且硬度较低,缝内支撑剂嵌入缝面较为严重;而颗粒支撑中砾岩砾石含量高,硬度较大,缝内支撑剂破碎严重;高铺砂浓度（5 kg/m2）条件下,提高闭合应力（大于60 MPa）,杂基支撑细砾岩、颗粒支撑中砾岩压后缝宽均大幅减小,导流能力较20 MPa低闭合应力时分别下降88%和92%。现场试验证实,在60 MPa以上高闭合应力下,保证高铺砂浓度的同时,使用高比例小粒径支撑剂,有利于增大运移距离,且支撑剂在粗糙缝内相对均匀铺置,裂缝导流能力较高,油井产量高且稳定。图13表4参19
True tri-axial sanding fracturing experiments are carried out on conglomerate samples from the Permian Wuerhe Formation of Mahu sag, Junggar Basin, to study hydraulic fracture propagation geometry and quartz sand transport in matrix-supported fine conglomerate and grain-supported medium conglomerate. The effect of rough fracture surface on conductivity is analyzed using the 3D-printing technology to reconstruct the rough surface formed in the fractured conglomerate. The hydraulic fractures formed in the matrix-supported fine conglomerate are fairly straight, and only more tortuous when encountering large gravels at local parts; thus, proppants can get into the fractures easily with transport distance about 70%-90% of the fracture length. By contrast, in the grain-supported medium conglomerate, hydraulic fractures tend to bypass the gravels to propagate in tortuous paths and frequently change in width; therefore, proppants are difficult to transport in these fractures and only move less than 30% of the fracture length. As the matrix-supported fine conglomerate has high matrix content and low hardness, proppants embed in the fracture surface severely. In contrast, the grain-supported medium conglomerate has higher gravel content and hardness, so the quartz sand is crushed more severely. Under the high proppant concentration of 5 kg/m2, when the closure stress is increased (above 60 MPa), fractures formed in both matrix-supported fine conglomerate and grain-supported medium conglomerate decrease in width significantly, and drop 88% and 92% in conductivity respectively compared with the case under the low closure stress of 20 MPa. The field tests prove that under high closure stress above 60 MPa, using a high proportion of fine proppants with high concentration allow the proppant to move further in the fracture; meanwhile proppant places more uniformly in the rough fracture, resulting in a higher fracture conductivity and an improved well performance.
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