| 利用含可控裂缝人工岩样研究裂缝密度对各向异性的影响 |
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| 引用本文： | 丁拼搏,狄帮让,魏建新,李向阳,邓颖华.利用含可控裂缝人工岩样研究裂缝密度对各向异性的影响[J].地球物理学报,2015,58(4):1390-1399. |
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| 作者姓名： | 丁拼搏 狄帮让 魏建新 李向阳 邓颖华 |
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| 作者单位： | 1. 油气资源与探测国家重点实验室, 中国石油大学(北京), 北京 102249;2. CNPC物探重点实验室, 中国石油大学(北京), 北京 102249;3. Edinburgh Anisotropy Project, Edinburgh, EH9 3LA, UK;4. 东方地球物理公司大港分院研究所, 天津 300280 |
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| 基金项目： | 国家重大专项(2011ZX05019-008)资助. |
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| 摘 要： | 利用新方法制作出含可控裂缝的双孔隙人工砂岩物理模型,具有与天然岩石更为接近的矿物成分、孔隙结构和胶结方式,其中裂缝密度、裂缝尺寸和裂缝张开度等裂缝参数可以控制以得到实验所需要的裂缝参数,岩样具有真实的孔隙和裂缝空间并可以在不同饱和流体状态下研究流体性质对于裂缝介质性质的影响.本次实验制作出一组具有不同裂缝密度的含裂缝人工岩样,对岩样利用SEM扫描电镜分析可以看到真实的孔隙结构和符合我们要求的裂缝参数,岩样被加工成八面棱柱以测量不同方向上弹性波传播的速度,用0.5 MHz的换能器使用透射法测量在饱和空气和饱和水条件下各个样品不同方向上的纵横波速度,并得出纵横波速度、横波分裂系数和纵横波各向异性强度受裂缝密度和饱和流体的影响.研究发现流体对于纵波速度和纵波各向异性强度的影响较强,而横波速度、横波分裂系数和横波各向异性强度受饱和流体的影响不大,但是对裂缝密度的变化更敏感.
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| 关 键 词： | 双孔隙物理模型 裂隙密度 纵横波速度 各向异性 横波分裂 岩石物理 |
| 收稿时间： | 2014-03-13 |
Experimental research on the effects of crack density based on synthetic sandstones contain controlled fractures |
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| DING Pin-Bo,DI Bang-Rang,WEI Jian-Xin,LI Xiang-Yang,DENG Ying-Hua.Experimental research on the effects of crack density based on synthetic sandstones contain controlled fractures[J].Chinese Journal of Geophysics,2015,58(4):1390-1399. |
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| Authors: | DING Pin-Bo DI Bang-Rang WEI Jian-Xin LI Xiang-Yang DENG Ying-Hua |
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| Institution: | 1. State Key Laboratory of Petroleum Resource and Prospecting, Beijing 102249, China;2. CNPC Key Laboratory of Geophysical Exploration, Beijing 102249, China;3. Edinburgh Anisotropy Project, British Geological Survey, Edinburgh, EH9 3LA, UK;4. BGP Dagang Branch, CNPC, Tianjin 300280, China |
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| Abstract: | Fracture development and distribution in underground rocks have strong influence on rock properties, understanding the fracture system is critical to the oil and gas reservoir detection and production, groundwater resource, underground wastes storage, mining, seismology and CO2 capture and storage.Due to the complex fracture distribution and geometry in nature rocks, the lack of information about fracture parameters (fracture density, length and thickness) makes the nature rock cannot be used in laboratory experiments. Rock physics experiments require the controlled and known fracture parameters and orientation in rock samples, thus synthetic samples were used to represent fractured rocks in several previous studies. However, the fractures were represented by other week material, such as silica rubber imbedded in epoxy solid, to simulate the fractured rocks in previous studies. The materials used to construct the samples (Lucite, silica rubber, sand bonded by epoxy) were very different from nature rocks, the solid representing background matrix and the week material representing fractures have no porous and fracture space and saturated fluids. In this study, we use new construction method based on material science progress to build synthetic samples which have similar mineral component, porous structure, cementation as nature rocks. The synthetic rock containing controlled fracture geometry provides a different way to create fractured rocks to observe the seismic anisotropy influenced by fracture parameters and fluids. The synthetic rocks are tested under high pressure to observe the pressure sensitivity, and SEM is used to observe the porous structure and fractures distrubution. We build a set of synthetic rocks to observe the effect of fractures upon seismic wave velocity and anisotropy. The samples are measured with 0.5 MHz transducers. P and S wave velocity in different propagation directions of these four samples are measured when saturated by air and water.The experimental results can help in investigating the relationship between fracture density and P and S wave anisotropy in fractured reservoirs. The measurement results show that the P wave velocity and anisotropy is significantly influenced by saturating fluid. Shear wave velocity, shear wave splitting and shear wave anisotropy are less sensitive to saturating fluid but significantly affected by fracture density. P wave velocities in perpendicular direction show significant influences of fracture, the velocity decreases as the fracture density increases. Shear wave velocity in perpendicular direction decreases with the increasing fracture density, the difference between fast shear wave and slow shear wave velocity is smaller in this direction. However the slow shear wave velocity is more sensitive to fracture density than fast shear wave velocity in parallel direction, thus the difference of fast and slow shear wave velocity in parallel direction increases as the fracture density increases. P wave velocity is more sensitive to saturating fluids, as the velocity is higher in water saturation than air saturation. P wave anisotropy is much higher in air saturation, but decreases while saturated by water. Shear wave velocity and anisotropy is less sensitive to fluid saturation, but is more sensitive to fracture density since shear wave anisotropy increases significantly with increasing fracture density.The new construction process can provide more realistic rocks for rock physics experiments, in which the fracture parameters can be controlled. The measurement results show that P wave velocity and anisotropy is very sensitive to fluid saturation, P wave anisotropy decreases while rock is saturated by fluid with higher modulus. Shear wave velocity is not sensitive to fluids but is significantly influenced by fracture density. |
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| Keywords: | Physical model Fracture density Elastic wave velocity Anisotropy Shear wave splitting Rock physics |
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