潜山花岗岩裂缝性储层阵列声波测井数值模拟研究
A numerical simulation study on array acoustic logging of fractured granite reservoirs in buried hills
通讯作者: 张冲(1983-),男,博士,教授,博士生导师,从事测井数据处理与综合解释的教学与研究工作。Email:yzlogging@163.com
责任编辑: 叶佩
收稿日期: 2023-06-15 修回日期: 2023-09-5
基金资助: |
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Received: 2023-06-15 Revised: 2023-09-5
作者简介 About authors
杜惟一(1999-),女,在读硕士,主要研究方向为测井数据处理与综合解释。Email:
南海琼东南盆地潜山储层储集空间类型复杂多样,裂缝多发育,导致储层具有较强的非均质性,该地区多见花岗岩沉积,因此有效评价花岗岩储层中裂缝的发育情况至关重要。利用COMSOL Multiphysics有限元模拟软件,采用有限元方法,对使用阵列声波测井探测不同宽度、不同倾角及不同长度的花岗岩储层进行模拟,总结出不同发育状态裂缝的阵列声波测井响应特征。研究发现:裂缝性地层横波受裂缝宽度变化影响不明显,横波衰减程度与裂缝倾角变化呈反比,与裂缝长度变化呈正比;斯通利波对裂缝宽度、裂缝倾角、裂缝长度等变化均有明显响应,斯通利波衰减程度与裂缝宽度及裂缝倾角均呈正比;在裂缝长度小于0.1 m时,斯通利波衰减程度与裂缝长度呈正比,裂缝长度大于0.1 m之后,斯通利波对裂缝长度变化无明显响应。本文研究结果为采用阵列声波测井方法判断花岗岩储层中裂缝的发育状态提供了依据。
关键词:
The buried-hill reservoirs in the Qiongdongnan Basin of the South China Sea exhibit intricate reservoir spaces and numerous fractures, leading to their pronounced heterogeneity. Since granite sediments spread across the study area, it is critical to effectively evaluate the development of fractures in granite reservoirs. Based on the COMSOL Multiphysics software and the finite element method, this study simulated the use of array acoustic logging to detect granite reservoirs with different widths, dip angles, and lengths, summarizing the response characteristics of fractures in different development states. The results are as follows: (1) Shear waves in fractured formations are subjected to non-significant influence of fracture widths, and their attenuation is inversely proportional to fracture dip angles and directly proportional to fracture lengths; (2) Stoneley waves manifest significant response to the changes in fracture widths, dip angles, and lengths, and their attenuation is proportional to both fracture widths and dip angles; (3) The attenuation of Stoneley waves is directly proportional to fracture lengths below 0.1 m but shows subtle response to fracture lengths above 0.1 m. The results of this study provide a basis for determining the development state of fractures in granite reservoirs using the array acoustic log method.
Keywords:
本文引用格式
杜惟一, 张冲, 韩华洋, 赵腾腾, 张文艺.
DU Wei-Yi, ZHANG Chong, HAN Hua-Yang, ZHAO Teng-Teng, ZHANG Wen-Yi.
0 引言
常规油气储层的裂缝勘探常使用阵列声波测井方法,国内外专家学者对此展开过不同的研究[7⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓-20]。综合前人的研究发现,在常规储层中,纵波对裂缝反映不敏感,横波及斯通利波受裂缝影响产生衰减[21⇓⇓-24]。帕尔哈提·祖努等[25]和齐兴华等[26]研究了煤层中不同裂缝宽度和不同裂缝条数下声波测井的响应特征。但目前鲜少有应用阵列声波测井方法开展花岗岩储层裂缝形态的研究,无法确定花岗岩储层中声波对裂缝的响应规律。因此,本文采用数值模拟阵列声波测井方法研究花岗岩储层裂缝的形态规律,即通过对花岗岩裂缝宽度、裂缝倾角、裂缝长度不同情况下的阵列声波测井数值模拟,来研究纵波、横波、斯通利波在不同裂缝情况下的声场响应规律,为采用阵列声波测井判断花岗岩储层中裂缝的发育状态提供依据。
1 模型建立
1.1 理论基础
式中:
式中:ρ为介质密度;u为振幅;S为第二类Piola-Kirchhoff应力张量;
1.2 模型设置
图1
表1 模型各材料参数
Table 1
材料设置 | 密度/ (kg·m-3) | 声速/ (m·s-1) | 杨氏模 量/Pa | 泊松比 |
---|---|---|---|---|
地层 井眼 裂缝 | 2600 1000 1000 | 5000 1500 1500 | 6×1010 0 0 | 0.5 0.25 0.25 |
发射探头所激发的波主频约为10 kHz。为了得到更精确的数值解,模型网格设置为极细化剖分,网格最大单元设置为0.02 m。模型中设置吸收边界,分别在花岗岩地层周围设置低反射边界,在井眼顶底设置平面波反射边界。
2 模拟结果
2.1 含裂缝模型模拟
图2
2.2 裂缝宽度变化模拟
保持其他条件不变,当裂缝为30°贯穿缝,裂缝宽度分别为10 μm、20 μm、50 μm、100 μm、200 μm、500 μm、1 mm、2 mm、5 mm时,裂缝在源距2.5 m处对声波的衰减结果如图3所示。可以看出,裂缝宽度的增加与裂缝对声波的衰减程度呈正比,缝宽小于100 μm时,裂缝对声波的衰减程度影响变小,裂缝小于20 μm时,缝宽的减小对声波的衰减情况基本不再改变;纵波、横波对裂缝宽度的改变无明显影响;斯通利波的到时并未有明显改变,但斯通利波的响应幅度与裂缝宽度的增加呈反比关系。
图3
图3
裂缝宽度与声压衰减的关系曲线
Fig.3
Relationship between crack width and sound pressure attenuation
2.3 裂缝倾角变化模拟
当裂缝宽度为100 μm,贯穿缝分别为0°、15°、30°、45°、60°、75°时裂缝在源距2.5 m处对声波的响应结果如图4所示。可以看出,当裂缝倾角为低角度(倾角<45°)时,声波响应值与裂缝倾角呈反比,声波衰减与裂缝倾角呈正比;当裂缝倾角为高角度(倾角>45°)时,声波衰减程度变大且相位发生变化;纵波对不同倾角裂缝的响应无明显变化。裂缝倾角在低角度范围时,裂缝倾角的增大和横波到时呈正比关系,与横波响应幅度呈正比关系。斯通利波到时未发现明显改变,斯通利波幅度值与裂缝倾角增加呈反比关系。裂缝倾角在高角度范围时,裂缝倾角的增大和横波到时呈正比关系,但由于相位发生改变且反射波发生叠加,与横波响应幅度关系无法确定;由于相位发生改变,斯通利波对高倾角裂缝的响应无明显规律。
图4
图4
裂缝倾角与声压的关系曲线
Fig.4
Relationship between crack inclination and sound pressure
2.4 裂缝长度变化模拟
当裂缝宽度为100 μm、裂缝倾角为30°时,裂缝长度分别为0.01、0.02、0.05、0.1、0.2、0.5、1 m和无限延伸长度时裂缝在源距2.5 m处对声波的响应结果如图5所示。可以看出,当裂缝长度小于0.1 m时,即裂缝主要分布在井壁周围时,裂缝长度增加与声波衰减程度呈正比且声波相位发生改变;纵波对裂缝长度变化不敏感;横波到时与裂缝长度增加呈反比,横波响应幅度与裂缝长度呈反比;斯通利波到时与裂缝长度增加呈正比,斯通滤波响应幅度与裂缝长度增加呈反比。当裂缝长度大于0.1 m时,此时裂缝主要分布在地层中,裂缝长度的增加对声波衰减程度的影响不明显;纵波对裂缝长度变化不敏感;横波到时与裂缝长度增加呈反比,横波响应幅度与裂缝长度呈反比,横波衰减程度与裂缝长度增加呈正比;斯通利波对裂缝长度变化无明显响应。
图5
图5
裂缝长度与声压衰减的关系曲线
Fig.5
Relationship between crack length and sound pressure attenuation
3 结果分析
由于纵波对裂缝响应变化相对较小,因此本文主要分析横波与斯通利波对裂缝的响应。
3.1 裂缝宽度对声波的影响
裂缝宽度变化对横波无明显影响,因此,此处主要分析裂缝宽度变化对斯通利波的影响。图6为裂缝宽度变化对斯通利波衰减的影响,其中声波衰减是指无裂缝模型的斯通利波声压值与含裂缝模型斯通利波声压值之差。从图中可以看出,裂缝宽度与斯通利波声压衰减具有很好的正相关性,且当裂缝宽度小于100 μm时,裂缝对斯通利波的衰减程度影响变小,裂缝小于20 μm时,裂缝宽度的减小不再对斯通利波的衰减程度造成影响。
图6
图6
裂缝宽度与斯通利波衰减的关系
Fig.6
Relationship between crack width and stoneley wave attenuation
3.2 裂缝倾角对声波的影响
图7为裂缝倾角对横波与斯通利波的影响。从图中可看出,横波到时在裂缝倾角增大时出现明显滞后,且当裂缝倾角小于30°时,横波到时受裂缝倾角影响较小,当裂缝倾角大于30°时,横波到时受裂缝倾角影响出现显著变化。因高角度(倾角>45°)裂缝相位发生变化,反射波出现叠加,所以此处主要分析低角度裂缝下横波与斯通利波的响应。裂缝倾角在低角度范围内时,横波响应声压与裂缝倾角呈正相关关系,即裂缝倾角越小横波衰减越明显;而斯通利波响应声压与裂缝倾角呈负相关关系,表明裂缝倾角越大斯通利波衰减越明显。
图7
图7
裂缝倾角与横波、斯通利波的关系
Fig.7
Relationship between crack inclination and transverse and Stoneleigh waves
3.3 裂缝长度对声波的影响
长度小于0.1 m的裂缝主要为井旁诱导缝。图8为裂缝长度<0.1 m时对横波与斯通利波的影响,其中横波衰减程度是指无裂缝模型的横波声压值与含裂缝模型横波声压值之差。从图中可以看出:横波到时与裂缝长度呈正相关关系,横波衰减程度与裂缝长度呈正相关关系;斯通利波到时与裂缝长度呈负相关关系,斯通利波衰减程度与裂缝长度呈正相关关系。
图8
图8
裂缝长度<0.1m时与横波和斯通利波的关系
Fig.8
Relationship between crack length (<0.1m) and transverse and Stoney waves
长度大于0.1 m的裂缝主要存在于地层中。图9为裂缝长度>0.1 m时对横波到时、横波衰减的影响,从图中可以看出横波到时与裂缝长度呈正相关关系,横波衰减程度与裂缝长度呈正相关关系。
图9
图9
裂缝长度>0.1m时与横波的关系
Fig.9
Relationship between crack length (>0.1m) and transverse wave
4 结论
本文通过使用COMSOL Multiphysics有限元模拟软件对阵列声波测井探测裂缝性花岗岩储层进行模拟,得出以下结论:
1)裂缝性花岗岩地层中,横波受裂缝宽度变化影响不明显,横波衰减程度受裂缝倾角与裂缝长度变化影响,裂缝倾角越小,横波衰减程度越大;裂缝长度越长,横波衰减越大。
2)裂缝性花岗岩地层中,斯通利波对裂缝宽度、裂缝倾角、裂缝长度等变化均有明显响应,即裂缝宽度越大,斯通利波衰减程度越大;裂缝倾角越大,斯通利波衰减程度越大;在裂缝长度小于0.1 m时,裂缝长度越大斯通利波衰减程度越大,在裂缝长度大于0.1 m时,斯通利波对裂缝长度改变无明显响应。
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基于反射声波测井有限元方法的井旁裂缝分布特征
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Near wellbore fracture distribution characteristics based on acoustic reflection logging finite element method
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裂缝对井眼声波的传播影响规律研究
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Studies on the effec of crack on the propagation of acoustic waves in wellbore
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基于线性滑动模型的裂缝性地层声波测井响应数值模拟
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Numerical simulation of acoustic logging in fractured formation based on linear-slip model
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多极子声波测井的裂缝识别与评价
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Fracture identification and evaluation based on multi-pole acoustic logging
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粗糙裂缝对井眼声波传播的影响
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Data influence of rough crack on borehole acoustic wave propagation
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三维声波测井探测特性分析与处理技术应用
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Analysis of detecting characteristics and application of data processing technology for 3D array acoustic logging
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裂缝模型声波衰减系数的数值模拟
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Numerical simulation of the fractured model acoustic attenuation coefficient
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用有限元法计算井中水平裂缝的反射斯通利波
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Computation of reflected stoneley wave at a horizontal fractures using finite element method
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裂缝性煤层声波测井响应的有限元模拟研究
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Finite element simulation of acoustic logging response in fractured coal seams
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