径向钻孔引导水力压裂裂缝定向扩展机理研究

Hydraulic fracturing by radial wells has become a new technology to effectively develop low-permeability reservoirs, thin reservoir, fractured reservoirs, “dead oil area” after water flood and depositional trap reservoirs. Due to the uncertainty of mechanism on hydraulic fracture directional propagation by the guidance of radial drillings, whether hydraulic fracture may be able to propagate smoothly along a single radial well direction to communicate the target area or not can’t be understood well, greatly limiting the application of this technology. For the conventional sandstone reservoirs, this project will first carried out the experimental study of hydraulic fracturing simulation based on vertical multi-radial wells, summarizing fracture propagating law and proposing the program of hydraulic fracture directional propagation. Then the mechanism of hydraulic fracture directional propagation will be revealed by carrying out the basic theoretical research. After that, a three-dimensional fracture propagation model used to stimulate hydraulic fracturing by radial wells will be established. The effects of crustal stress, radial well completion parameters, natural fractures, rock physical and mechanical properties, displacement, fracturing fluid viscosity on fracture initiation pressure, position and propagation shape will be studied. Mechanism and applicative conditions on hydraulic fracture directional propagation by the guidance of the single radial well will be understood well. Then the numerical simulation research on hydraulic fracture directional propagation by manual control based on the interference between the radial boreholes will be carried out. Through experimental study of hydraulic fracturing simulation, mechanical analysis and numerical simulation, the design theory and methods will be established to achieve the fracture directional propagation by overcoming stress control and the effects of heterogeneity. The study will reveal hydraulic fracture initiation and propagation mechanism by guidance of radial wells, and provide a reliable scientific basis for the effective implementation of hydraulic fracturing by radial wells. Meanwhile, the new technology on hydraulic fracture directional propagation by manual control will have important practical significance.

径向井水力压裂改造技术已成为有效开发低渗透油层、薄油层、裂缝性油气层、注水后“死油区”以及岩性圈闭油藏的新工艺技术。但由于径向钻孔引导水力裂缝扩展机理不明确，导致对于裂缝是否能够沿径向井方向延伸沟通目标区域认识不清，极大限制了该技术的应用。本项目针对常规砂岩储层，开展垂向多径向井水力压裂物理模拟实验，总结裂缝扩展规律，提出实现水力裂缝定向扩展的方案。进而开展基础理论研究，揭示定向扩展机理。最后建立用于模拟径向井水力压裂的三维裂缝扩展模型，研究地应力、径向井完井参数、天然裂缝、岩石物理力学性质、排量、压裂液粘度等对裂缝起裂和扩展的影响，明确单径向井引导水力裂缝定向扩展的机理和适用条件，进而开展基于垂向径向井孔间干扰实现人工控制裂缝定向扩展的数值模拟研究。通过水力压裂模拟实验、力学分析和数值模拟研究，建立克服地应力控制和非均质影响，实现裂缝定向扩展的设计理论和方法。该研究能够揭示径向井引导水力压裂的裂缝扩展机理，不仅可为径向井水力压裂技术的有效实施提供可靠的科学依据，同时人工控制裂缝定向扩展的新技术具有重要的实际意义。

径向井水力压裂改造技术已成为有效开发低渗透油层、薄油层、裂缝性油气层、注水后“死油区”以及岩性圈闭油藏的新工艺技术。但由于径向钻孔引导水力裂缝扩展机理不明确，导致对于裂缝能否沿径向井方向延伸沟通目标区域认识不清，极大限制了该技术的应用。此外，单一径向钻孔辅助水力压裂在很多情况下存在引导强度不足的问题。为此，创新性地提出了垂向多径向钻孔引导水力压裂裂缝定向扩展的设计思路。首先，针对常规砂岩储层，开展了垂向单一和多径向井水力压裂物理模拟实验，总结了裂缝扩展规律；进而充分考虑了原地应力、井筒内压以及压裂液渗滤效应对井筒周围地层应力场分布的影响，建立了两个径向孔条件下的理论力学模型，开展了垂向两径向钻孔辅助水力压裂裂缝起裂机理研究；最后利用Abaqus软件建立了垂向单一和多径向井辅助水力压裂的三维扩展有限元数值模型，全面考察了水平地应力差、径向井方位角、径向井井径、径向井间距、径向井长度、压裂液排量和粘度、岩石杨氏模量和泊松比以及储层渗透率等因素对径向井引导水力裂缝效果的影响。研究结果表明：径向井辅助水力压裂的裂缝起裂位置位于径向井跟部；径向井参数、储层物性参数和压裂施工参数之间相互影响、共同制约着径向井排对水力裂缝的引导效果；单一径向井辅助水力压裂引导强度有限，当水平地应力差或径向井方位角较大时，难以实现沿径向孔眼定向扩展，裂缝极易沿缝长和缝高方向产生扭曲；垂向上科学合理的布置多径向井，可有效实现水力裂缝的定向扩展，通过增加径向井井径和井数、减小井距和增大压裂液排量等可控措施可提高引导强度。通过水力压裂模拟实验、力学分析和数值模拟研究，建立了克服地应力控制和非均质影响，实现裂缝定向扩展的设计理论和方法。该研究能够揭示径向井引导水力压裂的裂缝扩展机理，不仅可为径向井水力压裂技术的有效实施提供可靠的科学依据，同时人工控制裂缝定向扩展的新技术具有重要的实际意义。