拉链式压裂中裂缝互作用与渗流力影响机理研究

Volume fracturing technology is the main technique for exploiting tight oil resource. Due to the different characteristics of tight oil reservoirs in China, the successful volume fracturing technology in oversea countries is difficult to form effective volume stimulation for some of the reservoirs. Zipper fracturing is a new technique of volume fracturing, and there are a few field application examples of obtaining high oil and gas production in the world. The basic idea of zipper fracturing is a fracture using another fracture’s changed local stress and seepage force fields, to create a complex fracture network to achieve effective reservoir volume stimulation. However, because of the fracture network formation mechanism of zipper fracturing is not mature, the most advanced international oil and gas company has come to a standstill..The concept of seepage force is introduced in the application. Two key scientific problems of seepage force on crack initiation and propagation and the interaction between the two fractures are solved by using laboratory experiment, theoretical and digital simulation methods. From the study of previous fracture’s new stress and seepage force fields, study the interaction of a later fracture close to the two fields and mechanism of forming complex fracture network. Finally, on the basis of improving single well production and ultimate recovery of zipper fracturing wells, optimizing the main parameters of well and fracture spacing, internal pressure of a later fracture, and the previous fracture length and its different internal pressures.

体积压裂技术是开采致密油的关键技术，由于我国致密油储层特征不同，国外成功的单井体积压裂技术对我国的部分储层难以形成有效的体积改造。拉链式压裂是体积压裂的一种新工艺，在国外已有获得高产油气流的现场应用实例。拉链式压裂的基本思想是一条裂缝利用另一条裂缝改变其周围的局部地应力场结果，造出复杂裂缝网络，实现储层有效体积改造。然而，由于拉链式压裂下的缝网形成机理尚不成熟，目前国际最先进的油气公司也裹足不前。.本申请引入渗流力概念，采用实验室实验、理论推导、数字模拟相结合的研究方法，拟解决渗流力对裂缝起裂扩展的作用机理，先后两条压裂缝的互作用机理两大关键科学问题。从研究拉链式压裂中先压裂的压裂缝对周围储层形成新的实地应力场和渗流力场出发，研究后压裂的压裂缝靠近该新力场时的互作用与形成复杂裂缝网络规律，最后以最终采收率为目标优化拉链式压裂的井间距、缝间距、缝内压力、裂缝长度等主要参数。

拉链式压裂作为非常规储层体积压裂的一种新工艺，其缝网形成机理仍然不清晰，参数优化设计方法仍然不成熟。基于此，项目围绕拉链式压裂裂缝互作用机理以及渗流力对裂缝起裂扩展影响机理两个关键科学问题开展系统研究，建立了渗流力理论力学模型和拉链式压裂裂缝扩展模型数值模拟器，开展了渗流力作用下水力裂缝起裂与拉链式压裂裂缝扩展数值模拟研究，探究了渗流力对井筒周围有效应力场和地层破裂压力的影响机理，明确了拉链式压裂裂缝间互作用与缝网形成机理。通过本项目的研究，主要取得以下几个方面的重要成果：（1）揭示了不同渗流参数和岩石力学参数影响下，井筒周围渗流力作用形成的应力场的变化规律，探究了渗流力作用对裸眼井筒有效应力场与地层破裂压力的影响机理；（2）研发了测量渗流力大小与模拟渗流力对岩石变形破坏作用的实验装置，填补了国内石油工程领域渗流力实验技术的空白；（3）明确了传统拉链式压裂与改进拉链式压裂裂缝扩展形态与裂缝互作用机制，揭示了缝间距、井间距、缝内压力等参数对拉链式压裂裂缝扩展行为的影响机理；（4）探究了基于裂缝间相互作用的水力裂缝网络形成机制，揭示了水力裂缝间的抑制、偏转与聚集作用，明确了诱导应力场的屏蔽效应与传递作用。（5）基于储层压后焖井的渗吸特征曲线建立了非常规致密砂岩储层分类新认识。本项目的研究成果为我国页岩气与致密油气开展拉链式压裂提供了重要的理论支撑，对拉链式压裂施工方案参数的优化设计具有实际指导作用。