THEORETICAL MODEL ABOUT FRACTURE POROSITY, PERMEABILITY AND STRESS FIELD IN THE LOW-PERMEABILITY SANDSTONE
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摘要: 低渗透砂岩储集层普遍发育裂缝, 裂缝不仅是重要的流体渗流通道, 而且在油井周围的发育程度直接影响着油井的生产能力.目前裂缝定量化预测方面存在的焦点问题是:缺乏一个有效而合理的力学模型, 裂缝渗透性的求取方法仍处于半定量化, 不具通用性.以史深100块沙三中储集层为目标, 从应力场和裂缝主要参数的关系入手, 以裂缝开度为桥梁, 通过实验和理论推导的方法, 建立了构造应力场和裂缝孔隙度、渗透率之间的定量关系模型.在岩石力学参数测试结果和地质模型建立的基础上, 对目的层裂缝发育时期的古构造应力和现今地应力进行数值模拟, 将结果代入关系模型, 计算研究区裂缝孔隙度和渗透率的空间分布, 进而指导低渗透砂岩油藏的裂缝参数定量预测、产能规划及井网部署.Abstract: Aiming at low-permeability sandstone, based on the principles of geological mechanics, using relationship between fracture parameters and stress field as a bridge, on the premise of reasonable preference of fracture criteria, through methods of tests and theoretical derivation, this paper establishes mechanical model between stress-strain and fracture parameters(porosity and permeability)to develop a set of quantitative methods. Results show that combining energy method with fracture criteria is effective approach to confirm the relationship between stress field and fracture parameters, after inner stress state reaching or exceeding failure conditions the fracture aperture, density will increase with strain energy density. At the same time, it is found that fractures in rock commonly formed under palaeostress field and their aperture and density were much larger than the present. Consequently, we can understand that current stress field goes against producing fractures and fracture aperture can be figured out through positive stress and shear stress acting on fracture face. Finally, Great success has been achieved in middle reservoirs of the third Shahejie Formation of Block Shishen100 in Shinan Oilfield by applying the program.
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图 1 σ1-σ3切面裂缝真实间距和视间距的关系
Figure 1. Relationship between the real spacing and apparent spacing of the fractures in σ1-σ3 shear plane
图 2 裂缝主平面和应力主平面示意图
Figure 2. A sketch map showing the main fracture plane and main stress plane
图 3 史深100块古应力场和现今应力场最大主应力(σ1)空间分布
Figure 3. Spatial distribution of maximum principal stress (σ1) in palaeostress field and present stress field in Block Shishen 100
图 4 史深100块沙三中3古应力场与现今应力场下裂缝开度分布
Figure 4. Fracture opening distribution under palaeostress field and present stress field in Block Shishen 100
图 5 史深100块沙三中3现今应力场下裂缝孔隙度分布及X方向裂缝渗透率分布
Figure 5. Distributions of fracture porosity and permeability in X-direction under present stress field in Block Shishen 100
表 1 裂缝计算开度、线密度和实测开度、线密度对比
Table 1. Comparison of calculated opening and linear density with measured opening and linear density
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