倾斜薄裂缝多孔地层的井眼声场

IF 1.6 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS
Yang Shouguo, Xie Fu-li, Gong Dan, Zhang Cheng-guang, Zhang Bixing
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grid finite difference method in order to satisfy the computation of thin fractures,the precision and speed of calculation are improved significantly.We process the fluid inside fractures through setting the parameters of constitutive functions as fluid limitation,which uniforms the difference equations on the fluid-porous media boundary and makes the computation more flexible.We investigate and compare many parameters influencing on the array waveforms,such as fracture width,fracture zone width,tilt angle and permeability.By the computations and analysis of borehole acoustic fields in different conditions,we can get conclusions as follows:1.The fractures barely influence body waves because the fracture width is much less than the acoustic wavelength,but the reflected shear wave and reflected Stoneley wave still could exist when Stoneley wave goes through the fracture.2.When the fractures are horizontal,only reflected Stoneley wave can be observed if the source is low 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引用次数: 3

摘要

随着全球油气勘探水平的提高,裂缝性储层成为勘探的重要对象之一。由于裂缝带分布的多样性,裂缝对测井阵列波形产生了复杂的影响,使得裂缝带的识别和评价成为声波测井的难点之一。本文采用数值模拟的方法研究了含倾斜裂缝的多孔地层包围下的井眼声场,并研究了不同裂缝参数地层的井眼场特征。采用三维交错网格应力-速度有限差分法,对倾斜裂缝含孔隙地层包围井中点源激发的声场进行了数值模拟。为了满足薄裂缝的计算,设计了一种非均匀网格有限差分法,大大提高了计算精度和速度。通过将本构函数参数设置为流体限制来处理裂缝内流体,统一了流-孔介质边界上的差分方程,使计算更加灵活。研究并比较了裂缝宽度、裂缝带宽度、倾角和渗透率等参数对阵列波形的影响。通过对不同条件下钻孔声场的计算和分析,得出以下结论:1.钻孔声场的分布;由于裂缝宽度远小于声波波长,裂缝对体波影响不大,但当斯通利波穿过裂缝时,反射横波和反射斯通利波仍然存在。当裂缝处于水平状态时,低频(2.5kHz)震源只观察到反射斯通利波,高频(5kHz及以上)震源同时存在反射横波和反射斯通利波。反射斯通利波的振幅随裂缝宽度的减小而减小,而反射横波的振幅不变。当裂缝宽度减小到20 m3时,反射横波仍然存在。裂缝带的密度和宽度对反射波的振幅有显著影响。当密度较小时,由于低密度导致小裂缝相互作用,反射波较弱;随着密度的增加,反射波变强。当裂缝穿过井眼并倾斜时,反射横波消失,而反射斯通利波仍然存在,这有利于倾斜裂缝的测试。斯通利波的衰减随渗透率的增大而增大。这导致裂缝边界处的弯曲斯通利波振幅减小,因此当裂缝距离震源较远时,无法观测到反射斯通利波。本文采用三维非均匀网格有限差分法,对含裂缝和裂缝带的多孔地层包围井眼的声场进行了数值模拟。通过计算和分析得出如下结论:裂缝上的斯通利波的弯曲导致反射横波和反射斯通利波的存在。反射斯通利波的振幅随裂缝宽度的减小而减小,而反射横波对裂缝宽度的变化不敏感,这有利于探测单薄水平裂缝的存在。反射斯通利波的振幅随裂缝带密度和宽度的增大而增大,当裂缝(裂缝带)倾斜时,反射横波消失,但反射斯通利波对裂缝角度的变化不敏感,这有利于探测倾斜裂缝带的存在。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Borehole acoustic fields in porous formation with tilted thin fracture
As the improvement of global oil and gas exploration,the fractural reservoir becomes one of the most important objects.The fractures complicatedly influence the array waveforms of logging because of the diversity distribution of fracture zone,which causes the recognition and evaluation become one of the most difficult problems in acoustic logging.In this paper,we research the acoustic field of the borehole surrounded by aporous formation with tilt fractures by numerical simulation,and also investigate the characteristics of borehole fields in the formations with different fracture parameters.We numerically simulate the acoustic fields excited by a point source in the borehole surrounded by aporous formation with tilt fractures using the 3-D staggered grid stress-velocity finite difference method.We design a non-uniform grid finite difference method in order to satisfy the computation of thin fractures,the precision and speed of calculation are improved significantly.We process the fluid inside fractures through setting the parameters of constitutive functions as fluid limitation,which uniforms the difference equations on the fluid-porous media boundary and makes the computation more flexible.We investigate and compare many parameters influencing on the array waveforms,such as fracture width,fracture zone width,tilt angle and permeability.By the computations and analysis of borehole acoustic fields in different conditions,we can get conclusions as follows:1.The fractures barely influence body waves because the fracture width is much less than the acoustic wavelength,but the reflected shear wave and reflected Stoneley wave still could exist when Stoneley wave goes through the fracture.2.When the fractures are horizontal,only reflected Stoneley wave can be observed if the source is low frequency(2.5kHz),while the reflected shear wave and reflected Stoneley wave both exist if the source is high frequency(5kHz and above).The amplitude of reflected Stoneley wave decreases when the width of fracture reduces,though the amplitude of reflected shear wave is unchanged.The reflected shear wave still exists when the fracture width reduces to 20 m.3.The density and width of fracture zone significantly influence the amplitude of reflected waves.When the density is small,the reflected waves are weak due to the low density causes the small fractures′interaction;as the density increasing,the reflected waves get stronger.4.When the fracture cross the borehole and tilt,the reflected shear wave disappears,however the reflected Stoneley wave still exists,this is good for testing tilt fractures.5.The attenuation of Stoneley waves increases along with the permeability increases.This causes the amplitude of inflected Stoneley waves on the fracture boundary decreases,so the reflected Stoneley wave could not be observed when the fractures are long away from source.In this paper,3-D non-uniform grid finite difference method is used to numerically simulate the acoustic field of the borehole surrounded by aporous formation with fracture and fracture zone.The conclusions are obtained by calculation and analysis as follows:The inflected Stoneley wave on the fracture causes the existence of reflected shear wave and reflected Stoneley wave.The reflected Stoneley wave′s amplitude decreases with the decrease of the fracture width,however,the reflected shear wave is not sensitive to the fracture width changing,this is good for detecting the existence of a single thin horizontal fracture.The reflected Stoneley wave′s amplitude increases along with the fracture zone density and width increasing;when the fracture(fracture zone)tilt,the reflected shear wave disappears,but the reflected Stoneley wave is not sensitive to the change of fracture angle,this is good for detecting the existence of the tilted fracture zone.
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来源期刊
地球物理学报
地球物理学报 地学-地球化学与地球物理
CiteScore
3.40
自引率
28.60%
发文量
9449
审稿时长
7.5 months
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