定面射孔对压裂初始裂缝形态的影响研究

Impact of Transverse Perforations on the Initial Fracture Shape of Hydraulic Fracturing

定面射孔是致密油水力压裂改造的一种新型完井措施。利用大尺寸真三轴水力压裂实验系统开展了300 mm×300mm×300 mm立方体试样定面射孔压裂物模试验,结合有限元三维应力分析,研究了定面射孔相位角对水力压裂初始裂缝形态的影响机制。研究结果表明:定面射孔各射孔道之间的应力干扰改变了近井筒应力分布格局,导致沿定面射孔方向水力裂缝呈倾斜状及迂曲状扩展,背离射孔方向裂缝形态为近垂直状形态。随射孔相位角减小,孔道间应力干扰增大、裂缝起裂压力提高,各射孔均产生破裂进而形成横向倾斜压裂平面。利用定面射孔技术可控制压裂初始裂缝呈非对称、非规则扩展形态,增加近井筒水力裂缝的复杂性。

The transverse perforation technique is a new perforation method for tight oil hydraulic fracturing. A large scale hydraulic fracturing experiments were conducted using an tri-axial physical simulation apparatus with 300 mm×300 mm×300 mm cube rock samples, and combined with the three-dimensional stress analysis using finite element method, the effects of transverse perforations azimuth angle on fracture propagation were studied. Research results show that the distribution of stress around wellbore changed by the stress interference among neighboring perforations. Tortuous fracture trajectory was observed along the direction of perforations, and vertical fracture in the opposing direction of perforations. With the decrease of transverse perforation azimuth angle, the stress interference is stronger and the breakdown pressure is increasing. Which leading to the fractures break on each of the perforations, and forming a transverse fracturing plane. The transverse perforation completion technique can control the initial fracture shape of hydraulic fracturing as a non-symmetric and non-regular extended pattern, and the fracture complexity of near wellbore was enlarged.