高温射流冲击-热裂解耦合破岩机理与实验研究

A key barrier to develop deep oil and gas reservoirs efficiently lies in improvement in penetration rate in deep formation. Conventional mechanical method can hardly meet the demand for oil and gas in China because of its low penetration rate, long cycle and high cost. Based on impingement of high temperature jet, thermal spallation method can enhance penetration rate in hard formations significantly. However, it has a narrow application scope due to its high demand for fluid temperature and rock properties. Inspired by high pressure water jet rocking breaking method, this proposal presents a new efficient drilling approach, which integrates rock thermal spallation principle and high pressure jet rock breaking method. High pressure and high temperature jet is formed downhole to impinge on the rock surface, causing the rock to crack. With rapid heat transfer and jet impingement, these cracks will expand and then the rock will be crushed efficiently. Therefore, this proposal will focus on the following aspects. First, distribution characteristics of temperature and pressure of the impinging flow field caused by high pressure thermal jet are studied through numerical simulation and laboratory experiments. Then, through AE and CT methods, rock dynamic damage and fragmentation process under high temperature and pressure jet impingement are studied to reveal the mechanism of jet impingement and thermal spallation in rock breaking. The threshold temperatures and pressures of different rocks are also determined by experiments to clarify the influence on rock breaking efficiency of jet parameters and rock properties. Through the research mentioned above, the results will be able to reveal the mechanism of rock breaking by integration of thermal spallation and jet impingement and provide an initial theoretical basis for hydrothermal jet drilling method.

深层油气资源勘探开发是国家油气发展的重大需求，但深部地层岩石硬度高、可钻性差，导致钻井周期长、成本高，提高深井硬地层破岩效率是亟待解决的关键问题之一。结合高压水射流和流体热裂解破岩方法，课题提出高温射流冲击和热裂解耦合破岩新思路：高温高压射流作用于井底岩石，诱导岩石热裂解产生裂缝，并在射流冲击下加速裂缝扩展，有望实现二者耦合作用下岩石的高效破碎。拟开展以下研究：数值模拟和实验研究井下淹没环境中高温高压射流的冲击流场，得到岩石表面非均匀温度场和冲击压力场的分布特征；基于声发射和CT扫描方法，研究高温射流作用下岩石的动态损伤破碎过程，揭示热裂解和射流冲击在破岩过程中的作用机制；实验研究不同岩石的破岩门限温度和压力，探索射流参数和岩石物性对破岩效率的影响规律。通过上述研究，旨在揭示热裂解和射流冲击耦合作用下岩石的破碎机理，探索高温射流提高深井硬地层钻井速度的可行性，为深井钻井提速提供一种新途径。

深层油气资源开发是国家油气发展的重大需求，提高深井硬地层的破岩效率是亟待解决的关键问题之一。结合高压水射流和流体热裂解方法，项目提出了高温射流的破岩新思路，即采用高温高压射流作用于井底岩石，使得岩石在高温作用下产生微裂缝，并在射流作用下加速扩展，有望实现二者耦合作用下岩石的高效破碎。本项目采用数值模拟和实验的方法，系统的研究了高温射流冲击流场和破岩机制。首先，建立了井底淹没环境下高温射流冲击流场数值模型，揭示了围压下高温射流冲击传热动态演化规律，为揭示热裂解和射流冲击耦合作用下破岩机理提供基础。其次，采用有限元法建立了岩石内部动态传热与应力数值模型，研究了岩石内部温度与应力分布规律，揭示了非均匀热应力是破岩的关键。再次，设计研制了高温高压超临界水环境下岩石损伤实验装置，研究了超临界水浸泡下花岗岩成分、强度、波速变化，揭示了花岗岩在超临界水作用下的损伤特性与裂缝分布特征。最后，分析了花岗岩破碎形态与岩屑特征，实验和模拟研究了热破岩中的破岩门限温度，建立了高温射流作用下钻速模型和破岩比能模型，揭示了影响高温射流破岩效率的关键因素。本项目可为深井钻井提速探索一种新思路。研究成果在Applied Thermal Engineering、Journal of Petroleum Science and Engineering、Geothermics等期刊发表论文11篇，其中SCI检索10篇、EI检索1篇，TOP期刊4篇；出版英文专著1部；已授权国家发明专利4项，申请发明专利4项，登记软件著作权1件；国内外学术会议报告6次；培养博士研究生2名、硕士研究生1名。项目研究成果在2017年国家自然科学基金在研项目交流会中获“优秀报告奖”。