致密油压裂水平井渗流机理研究

The development of tight oil is a new technology in petroleum industry,and it has been aware of the potential after shale gas in the global unconventional oil and gas exploration and development,so the tight oil is called “Black Gold” in petroleum industry. But the pore structure and fluid flow mechanism of tight oil are not clear now.Due to the ultra low permeability i.e. micro nano - nano scale and complex pore structure in tight oil,the permeability is less than 0.1 md, there is a big difference in fluid diffusion law between conventional sandstone and low permeability oil reservoirs. Especially after the stimulation,the flow mechanism becomes more complicated due to the coupling effect of fluid micro-scale flow and stimulated fracture macroscopic flow, which can not be described with the existing theory and methods..The project aims for the coupling flow mechanism of fluids in the matrix,natural fracture and stimulated fracture in horizontal well. The method of physical model and reservoir numerical simulation will be used to study the physical property distribution in tight oil , stress sensitivity characteristics and matrix flow rule in sub-micron pores, considering the the coupling effect of fracture network flow and nanometer level pore flow.The mathematical model of productivity prediction for single horizontal fractured well will be established with the consideration of starting pressure and stress sensitivity. The effective displace theory and method for the flooding system will be established, which provides theoretical support for the effective development of tight oil.

致密油开发是一种新兴的石油技术，是继页岩气之后全球非常规油气勘探开发的又一新热点，因此被石油工业界誉为“黑金”。致密油储层由于其微纳-纳米尺度孔隙和复杂的孔隙结构，其内部流体的运移机理还不明确，渗流规律与常规砂岩储层有很大差别。致密油水平井压裂后储层微尺度流动与人工裂缝宏观流动耦合作用的渗流机理复杂，用现有的渗流理论和方法无法描述。本项目以致密油水平井压裂后流体在基质、天然裂缝及人工裂缝内的耦合渗流规律为研究目标，采用物理模拟和数值模拟研究相结合，开展致密油储层物性分布规律、应力敏感性特征和基于裂缝流动与次微米级基质流动的渗流规律研究，考虑流体在复杂裂缝网络与纳米级孔喉流动耦合作用下的渗流机理，建立考虑启动压力及应力敏感条件下水平井分段压裂后的产能预测数学模型，研究致密油有效驱替机理，分析影响致密油产能的因素，探索致密油渗流的基本规律，为致密油有效开发提供理论支持。

致密油作为非常规能源之一，其内部流体运移机制尚不明确。由于致密油储层复杂的孔隙结构，致密储层中流体的运移规律与常规砂岩储层有很大差别，现有的渗流基本理论无法对其进行准确表征与描述。本项目以致密油水平井多段压裂后流体在基质、天然裂缝及人工裂缝内的耦合渗流为目标，采用物理模拟和数值模拟相结合的方法，开展致密油储层物性特征和渗流机理、应力敏感和基于天然裂缝、人工裂缝与次微米级基质流动的渗流规律研究，形成致密油有效驱替理论和方法。.项目通过致密油启动压力梯度实验、应力敏感性实验、毛细管实验和致密储层有效驱替实验等分析了致密油储层物性分布特征及应力敏感性特征，研究了基于微尺度流动效应的致密油渗流规律。建立考虑致密油次微米孔喉基质的启动压力梯度、应力敏感性和微尺度效应的水平井多级压裂的裂缝宏观流动与基质微尺度流动耦合作用的渗流模型，模型内区为人工裂缝及压裂开启的天然缝形成的微裂缝网络与基质组成的双重介质，外区为单一基质。模型中充分考虑了启动压力梯度、压敏效应、毛管力，以及生产过程中人工裂缝导流能力失效性的影响。应用流量连续性推导了双重介质油藏与人工裂缝之间、缝与井筒之间的流量，通过油藏-裂缝的流量交换、裂缝-井筒的流量交换建立了三者之间的耦合关系。.实验结果表明：长7致密岩心有应力敏感性，岩心渗透率随着有效压力的增大而减小；岩心的油、水两相的启动压力梯度与渗透率为乘幂关系，启动压力梯度先是急剧减小再逐渐趋于平缓；动态毛细管效应在常规油藏中不明显，但在致密油藏中十分明显，必须予以考虑。.数值模拟结果表明：压裂段数、每段压裂簇数、裂缝半长、微裂缝渗透率和导流能力是影响产能的关键因素。通过正交化方案设计可知，裂缝长度对致密油藏波及范围有重要作用，裂缝条数其次（压裂段数、压裂簇数）、裂缝导流能力对波及范围影响最小。