Analysis of the Influence of a Natural Fracture Network on Hydraulic Fracture Propagation in Carbonate Formations
Analysis of the Influence of a Natural Fracture Network on Hydraulic Fracture Propagation in Carbonate Formations
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DOI：
10.1007/s00603-013-0414-7
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发表时间：
2014-03-01
影响因子：
6.2
通讯作者：
Zhang, Guangqing
中科院分区：
文献类型：
--
作者：
Liu, Zhiyuan;Chen, Mian;Zhang, Guangqing
利用三轴压裂系统，设计了一个新的实验模型来模拟天然裂缝网络对天然裂缝扩展几何形状的影响。在该模型中，通过在立方模具中放置水泥板并在模具中填充额外的水泥来创建一个平行和对称的预破裂网络，以创建最终的测试块。因此，板的表面将被弱胶结并形成预断裂。预裂的尺寸和方向可以通过板来控制。试验结果表明，水平应力差和最大水平主地应力与裂缝前的夹角是水力裂缝起裂和扩展的主导因素。对于和或和，水力裂缝的起裂和扩展方向与裂缝前的正常方向一致或偏离。当水力裂缝接近裂缝前时，水力裂缝的扩展方向将与裂缝前的法向一致。否则，水力裂缝将偏转并垂直穿过平行和对称的裂缝前网络。对于和、和或和，在水力裂缝与预缝相交之前，水力裂缝的扩展方向保持不变，当水力裂缝扩展到交点时，预缝张开或扩张，形成一个复杂的水力裂缝网络，整个水力裂缝网络的扩展区域呈椭圆形。在这种情况下，水力裂缝的复杂程度由净压力、作用于裂缝前的压正应力、软弱面的抗剪强度和内聚强度控制。本研究的结论与以往研究普遍接受的接近角的表述不一致。水力裂缝扩展遵循阻力最小、扩展最优先、扩展路径最短的原则。
A new experimental model has been designed to simulate the influence of a natural fracture network on the propagation geometry of hydraulic fractures in naturally fractured formations using a tri-axial fracturing system. In this model, a parallel and symmetrical pre-fracture network was created by placing cement plates in a cubic mold and filling the mold with additional cement to create the final testing block. The surface of the plates will thus be weakly cemented and form pre-fractures. The dimension and direction of the pre-fractures can be controlled using the plates. The experiments showed that the horizontal differential stress and the angle between the maximum horizontal principal in situ stress and the pre-fracture are the dominating factors for the initiation and propagation of hydraulic fractures. For and or and , the direction of the initiation and propagation of the hydraulic fractures are consistent with or deviate from the normal direction of the pre-fracture. When the hydraulic fractures approach the pre-fractures, the direction of the hydraulic fracture propagation will be consistent with the normal direction of the pre-fracture. Otherwise, the hydraulic fracture will deflect and perpendicularly cross the parallel and symmetric pre-fracture network. For and , and or and , before the hydraulic fracture and the pre-fractures intersect, the direction of the hydraulic fracture propagation remains unchanged, and the pre-fractures open or dilate when the hydraulic fracture propagates to the intersection point, forming a complicated hydraulic fracture network with the propagation region of the overall hydraulic fracture network taking the shape of an ellipse. In this condition, the complexity level of the hydraulic fracture is controlled by the net pressure, the compressive normal stress acting on the pre-fractures, the shearing strength and the cohesion strength of the planes of weakness. The conclusions of this research are inconsistent with the formulation of the approach angle that has been widely accepted by previous studies. The principle of hydraulic fracture propagation is that it follows the least resistance, the most preferential propagation, and the shortest propagation path.