The influence of multi-metal-veins on fractures propagation investigated by the experiment and simulation

Fracture propagation is affected by multi-metal-veins formed by geological diagenesis in shale during the hydraulic fracturing.However,the influence of multi-metal-veins on fractures propagation remains unclear.To solve the problem,based on the semi-circle bending(SCB)test and the extended finite element(XFEM)theory,the interaction between multi-metal-veins and fractures is investigated.The experimental results reveal that the fractures usually deflect at the upper or lower interfaces between metal veins and rocks(e.g.the specimen S-2),which is different from the propagation behavior of fractures in calcite veins.Meanwhile,the fracture toughness of the specimen S-1 is 24.40%higher than that of the specimen S-2,indicating that the increasing of total thickness of multiple metal veins in-creases the resistance to the fracture vertical propagation.The simulation results show that the increasing of the number,total thickness of veins,the modulus difference between veins and rock,the approach angle and the notch angle all increase the resistance of the fracture passing through metal veins.The maximum deviation distance(Dmax)of the fracture decreases with the number of veins,while thickness combination types of metal veins do not affect Dmax.The reduction of the notch angle leads to the more tortuous fracture propagation path.Finally,we propose a new comprehensive fracture network pattern.Fracture networks are divided into two categories,including orthogonal fracture networks and sub-orthogonal fracture networks,and then divided into six sub-categories further.The research results will provide reference for hydraulic fracturing of shale reservoirs containing multi-metal-veins.

巨厚砂砾岩储层X形水力裂缝的形成——以中国渤海湾盆地储层为例

中国渤海湾盆地致密砂砾岩储层广泛发育,它们通常为深埋巨厚储层,其有效开发需依赖水力压裂技术。为了研究砂砾岩储层水力裂缝的扩展特征,首先,探究了此地砂砾岩储层的地质条件,包括地层纵向分布规律和岩性特征;然后,通过地面微地震系统对该地区盐222区块几口井的压裂过程进行了监测。结果表明,目标井大多数地层压裂后均形成了X形水力裂缝。本文将储层形成X形水力裂缝的主要原因归于(1)储层非均质性和(2)两条近距离同向扩展的水力裂缝的应力阴影效应,并通过数值模拟等方法对其进行了详细分析和验证。本文的研究成果和结论可为巨厚砂砾岩储层水力裂缝扩展特征的深入研究提供参考依据。