不同脆性致密砂岩裂缝扩展规律实验

岩石的脆性与致密油气储集层压裂改造效果密切相关,但致密岩石的脆性对裂缝扩展规律的影响仍不明确。基于真三轴压裂模拟实验系统,对鄂尔多斯盆地东部3种不同脆性致密砂岩开展了压裂模拟实验,分析了脆性、压裂液类型和层理对裂缝扩展规律的影响。研究表明,山1段致密砂岩脆性最强,长7段致密砂岩次之,盒8段致密砂岩脆性最弱;在层理不发育的条件下,相比于中等脆性的盒8段致密砂岩,强脆性的山1段致密砂岩采用滑溜水压裂形成的单条裂缝扩展更充分,液态CO₂压裂形成的分支裂缝数量更多;在层理发育的条件下,长7段致密砂岩采用滑溜水压裂和液态CO₂压裂形成的裂缝的形态均较复杂;相比于滑溜水压裂,液态CO₂压裂形成的裂缝宽度更小;液态CO₂压裂更适用于脆性较强、层理发育的长7段致密砂岩储集层压裂改造。

Experiments on Hydraulic Fracture Propagation in Tight Sandstones with Different Brittleness

Rock brittleness is closely related to the effectiveness of fracturing treatment in tight reservoirs, but the influence of the brittleness of tight rock on fracture propagation is still unclear. In order to study how hydraulic fractures propagate in tight sandstones with different brittleness, fracturing experiments were conducted on three types of tight sandstone using a true tri-axial fracturing simulation system. The influences of rock brittleness, fracturing fluid and bedding on fracture propagation were analyzed. Experimental results show that Shan-1 tight sandstone has the strongest brittleness,followed by Chang-7 tight sandstone, and He-8 tight sandstone has the weakest brittleness. In the case with less beddings, the fracture induced by slick water extends more completely, and more fracture branches are created by liquid CO₂ in the most brittle Shan-1 tight sandstone than the He-8 tight sandstone. In the case with more beddings, the fracture shapes induced by liquid CO₂ in Chang-7 tight sandstone are more complex than those in the relatively homogeneous Shan-1 and He-8 tight sandstones. Compared with slickwater, the fractures induced by liquid CO₂ is narrower. Liquid CO₂ fracturing is more suitable for the most brittle Chang-7 tight sandstone reservoir with many beddings.