多场多相条件下超临界二氧化碳粒子射流破岩和井筒携岩机理研究

The unconventional oil and gas have become China's main alternative energy with the rapid growth of economy as well as the implementation of new energy strategy. However, there are still many problems to be solved in the development process of unconventional reservoirs. Such reservoirs can not be effectively developed using conventional drilling and production technologies, so it is urgent to develop new drilling and completion technologies. Because it has low interfacial tension and high density characteristics, the supercritical carbon dioxide can be used as drilling and completion fluids while avoiding reservoir damage and solving a lot of problems encountered during the development of unconventional oil and gas. Then a kind of high-efficient drilling and completion integration technology for the development of unconventional reservoirs is expected to be formed using this fluid. Practice has proved that the particle jet drilling is an important way to improve the drilling rate in hard formations. The higher rock-breaking efficiency can be obtained at lower jet pumping pressure if the particles are introduced into supercritical carbon dioxide jet, and the application feasibility of supercritical carbon dioxide jet in drilling and completion can be further enhanced. The project intends to study the force analysis of particles in the jet, establish the supercritical-phase and solid-phase turbulent flow equations, and reveal the rock-breaking and wellbore cuttings-carrying mechanism of supercritical carbon dioxide particle jet combining experimental research method and numerical simulation analysis method. Finally the project wishes to lay the theoretical foundation for the development of supercritical carbon dioxide jet drilling and completion methods and promote the efficient development of unconventional oil and gas reservoirs.

随着国家经济发展对能源需求量的急剧增长以及油气能源新战略的实施，非常规油气已经成为我国主要的接替能源，但在开发过程中尚存在很多难题亟待解决，采用常规钻采技术难以有效开发此类油气藏，亟需发展新型钻完井技术。利用超临界二氧化碳的低界面张力和高密度特性，作为钻井和完井流体介质，可以避免储层伤害，解决非常规油气开发过程中遇到的很多难题，有望形成一种高效的非常规油气藏钻完井一体化技术。钻井实践证明粒子射流破岩是硬地层提速的重要途径，将粒子引入到超临界二氧化碳射流中，可在更低的泵压下获得更高的破岩效率，进一步提升超临界二氧化碳射流应用于钻完井的可行性。本项目拟结合射流破岩过程中粒子的受力分析，建立超临界流体和固体两相湍流流动方程组，运用试验研究和数值模拟分析相结合的方法，揭示超临界二氧化碳粒子射流破岩和井筒携岩机理，为形成超临界二氧化碳射流钻完井方法奠定理论基础，促进非常规油气藏的高效开发。

本项研究采用装置研制、理论分析、数值模拟与实验研究相结合的研究方法，对多场多相条件下超临界二氧化碳粒子射流破岩机理及井筒携岩机理进行了较为系统的研究：首先，为了保证超临界二氧化碳射流破岩和携岩过程的安全，分析了各因素对超临界二氧化碳携岩的影响规律，建立了相关流动方程组，分析了粒子和岩屑在超临界二氧化碳中的沉降规律及最小环空返速，为本项目后续超临界二氧化碳实验装置研制、井筒携岩机理和破岩规律研究奠定了理论基础；其次，依据二氧化碳在井筒内的流动和传热特点，考虑研究所需要的多场多相条件，优化了超临界二氧化碳粒子射流破岩实验流程，研制了配套的粒子注入设备，采取模块化设计方法建立了超临界二氧化碳射流破岩和携岩实验装置；第三，优选了适用于破岩系统的粒子类型和非常规油气藏岩石类型，开展了多场多相条件下超临界二氧化碳粒子射流破碎页岩和致密砂岩的破岩探索性试验，发现了不同条件下超临界二氧化碳粒子射流的破岩特性，并与纯超临界二氧化碳射流等的破岩性能进行了对比分析；第四，基于所建立的携岩实验装置，进行了超临界二氧化碳携岩实验研究，获得了不同流速、不同井斜角条件下，超临界二氧化碳的携岩效率，在室内实验的同时，建立了超临界二氧化碳流体井筒携岩模型，采用数值模拟方法，分析了温度、压力、工程参数等对超临界二氧化碳携岩效果的影响。研究成果为形成超临界二氧化碳粒子射流破岩钻井方法奠定了理论基础，有助于促进超临界二氧化碳射流破岩钻井技术在非常规油气藏中的应用、提高非常规油气采收率。