共查询到19条相似文献，搜索用时 187 毫秒
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采用柱状成层介质的并矢Green函数高效计算井眼中偏心发射源产生的电磁波,并利用该算法模拟了阵列感应测井仪器在井眼中偏心时的响应.在模拟时既考虑到了金属心轴的存在也考虑到了线圈系所处绝缘层的存在,并重点分析了绝缘层的影响.数值模拟结果表明,对相对低泥浆电导率情况而言,无论线圈距长短,线圈系所处绝缘层对仪器响应的影响均较小,可忽略不计.而对于相对高泥浆电导率情况,线圈系所处绝缘层对仪器响应的影响明显,不可忽略,且线圈距越短影响越大,仪器偏心距越大影响越大.另由数值模拟结果可以看出,在相同泥浆电导率情况下,仪器线圈距越短偏心对线圈系响应的影响越大. 相似文献
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《地球物理学进展》2015,(4)
地层电阻率是影响油气或煤层气评价的重要参数,水平井中常利用感应测井确定地层电阻率,由于水平井与直井测量环境有较大差异,响应方式势必与直井不同.水平井测井响应的环境影响复杂,不能使用基于几何因子的信号处理,必须通过三维正演数值模拟方法研究响应特征.本文利用基于有限元方法的COMSOL Multiphysics软件对三层对称地层模型中的水平井感应测井响应进行了数值模拟分析.通过分析比较源距为0.3m、0.6m、0.9m、1.2m的四个水平线圈系的响应特征发现,不同源距的线圈系测得的电导率值受仪器位置、上下围岩电导率、目的层厚度和仪器偏心的影响规律不同.数值模拟结果对水平井的解释工作及仪器研发具有指导性意义. 相似文献
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采用偏心状态下柱状成层各向异性(横向各向同性)介质中并矢Green函数的解析表达式高效模拟多分量感应测井仪器在井眼中偏心时的响应.为提高精度,在模拟时考虑到了金属心轴、绝缘保护层的存在以及各分量线圈系的具体形状.数值模拟结果表明,当井眼内钻井液电导率相对较高、地层电导率相对较低时,偏心对仪器响应的影响较大,尤其是对短线圈距线圈系的影响更为明显,必须进行偏心效应校正.当钻井液电导率相对较低时,偏心对线圈系响应的影响可忽略不计.对位于相对低电导率井眼中的线圈系而言仪器方位角的影响可忽略不计,而当线圈系位于相对高电导率井眼中时仪器方位角的影响极为明显.当仪器偏心率较小时线圈系的响应随仪器方位角的变化较小,仪器偏心率越大线圈系的响应随仪器方位角的变化越明显. 相似文献
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随钻地质导向钻井的关键在于对边界的探测,为提高仪器探测深度,时谐源激励的电磁波测井方法通常采用降低频率、增大源距的方式.瞬变电磁波测井信号源的突然关断产生会产生感应涡流,涡流随时间向地层深部扩散,与时谐源激励方式相比,其探测深度更大且测量过程不受信号源的干扰.因此,本文提出一种时间域瞬变电磁波测井边界远探测方法,采用余弦变换的数值滤波算法,模拟层状地层同轴发射接收线圈的瞬变电磁波测井响应,结果显示,地层电导率越大,电磁波传播速度越慢,测量晚期感应电动势与地层电导率线性相关;通过定义层状介质总场与线圈系所在当前层背景场的差值可方便提取界面信息,对界面的探测距离可达数十米;瞬变电磁波测井响应受源距的影响很小,为利用短源距实现远探测提供了可能.瞬变电磁波测井与时谐源电磁波测井相比优势明显,在电磁波测井领域中应用前景广阔. 相似文献
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采用递推矩阵方法计算各向异性介质的磁流源并矢Green函数,并利用上述并矢Green函数对层状各向异性倾斜地层中多分量感应测井的响应进行数值模拟,分析了线圈距、层厚、倾角和围岩对多分量感应测井响应的影响.计算发现,共面视电导率比共轴视电导率变化规律复杂,不能反映地层电导率的真实情况.各向异性地层共轴视电导率随井眼相对倾角的增加而减小,而共面视电导率随井眼相对倾角的增加而增加.仪器的垂向分辨率、围岩各向异性对目的层响应的影响程度取决于线圈距,围岩各向异性对高电导率目的层中测井响应的影响大于对高电阻率目的层中测井响应的影响. 相似文献
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现有海洋可控源电磁三维数值模拟方法大多基于电导率各向同性介质理论,不能模拟海底地层电导率各向异性的实际情况.本文给出了电导率各向异性三维介质中电性源海洋可控源电磁二次电场的边值问题以及相应的变分问题,采用长方体单元对研究区域剖分,将场分量定义在剖分单元的边上,利用矢量有限单元法求解变分问题,实现了电导率任意各向异性海洋可控源电磁三维矢量有限元数值模拟.这个新的正演方法可以计算电导率任意各向异性三维地电模型的海洋可控源电磁响应,基于二次场矢量有限元法直接求解电磁场,避免了传统有限元方法可能遇到的伪解问题和难于处理电场法向分量不连续的问题,提高了数值模拟计算精度.一维电导率各向异性模型电磁场数值解与解析解吻合得相当好,无论在源附近还是远离源处相对误差均不超过1%.电导率各向异性二维模型的计算结果与已有文献采用的非结构有限元模拟结果十分吻合.三维地电模型数值模拟结果显示,电导率各向异性张量电导率主轴分量和欧拉角对不同装置海洋可控源电磁响应均有着明显的影响. 相似文献
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同时考虑电导率和位移电流的影响 ,导出了基于A -Φ的一个新泛函表达式 ,并开发了能在宽频段内模拟电磁测井响应的三维有限元程序。计算了水平磁偶线圈和垂直磁偶线圈的场分布 ,也给出了倾斜井中感应测井的响应 ,最后分析了线圈半径和各向异性的影响 相似文献
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本文将应用2.5维数值模式匹配算法研究建立柱状横向同性地层中偏心条件下磁流源并矢Green函数的高效算法,并利用该算法高效计算多分量阵列感应井眼校正库.首先,通过Fourier展开技术将偏心条件下磁流源并矢Green函数的数值模拟转化为一系列的轴对称问题;然后利用模式匹配算法求解轴对称问题,得到柱状介质中偏心条件下磁流源并矢Green函数的半解析解;最后,结合中国石油集团测井有限公司开发的三维感应测井仪器(TDIT)的结构参数,推导出复合线圈系视电导率张量的计算公式.在此基础上,根据井场实际地层资料归纳出理论地层模型相应参数的变化范围,高效高精度建立一套直接应用于工业生产的多分量阵列感应井眼校正库,并利用井眼校正库详细地分析考察各模型参数对TDIT响应的影响. 相似文献
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本文开发了基于非结构化四面体网格的三维矢量有限元法,实现了固体矿床井眼中多分量感应测井响应的数值模拟,并分析了多分量感应测井仪器在复杂矿床模型中的响应特征.本文通过采用几何因子背景场,有效地避免了源的奇异性问题;同时,在井眼边界采用非均质网格并用Gauss-Legendre积分计算四面体单元的等效电导率.利用LU分解求解线性方程组,实现了一次网格划分多点的数值计算,提高了计算效率,从而实现快速连续的多分量感应测井模拟.非结构化的四面体网格确保了该方法可以模拟实际问题中所能遇到的复杂的矿体模型.基于水平三层分层和径向分层模型,验证了算法在各向同性和各向异性介质中的可靠性.我们还以三个不同的矿床模型为例,研究了多分量感应测井仪的不同分量的探测特性,结果表明,结合九个分量的信息,可以探测矿体的深度,也可以识别矿体的方位和走向,为精确地描述矿体的三维分布特征打下了基础. 相似文献
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三轴张量感应测井可探测地层电导率各向异性,Zhdanov et al.利用在横向各向同性均匀介质中测井响应的低频渐近式给出了由张量感应测井响应提取地层各向异性电导率和井孔倾角与方位角信息的解析公式,为张量感应测井资料解释奠定了基础.但是,他们给出的井孔倾角公式存在双值解的不确定性,其各向异性电导率解也不是最佳近似解.本文以更为简洁的推导和分析方法,给出了单值的井孔倾角解以及近似程度更好的各向异性电导率解,并通过数值模拟实例加以说明.本文的结果可为张量感应测井资料的视值解释提供更好的选择. 相似文献
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A novel fixed-source electromagnetic system has been developed. The transmitter is a large rectangular loop or grounded dipole. The transmitted waveform consists of up to five superimposed pure sinusoids at well-separated frequencies. The receiver measures the amplitude and phase at two frequencies from a single receiver coil. The amplitude ratio is routinely calculated. Field trials with both surface and downhole configurations show that the method has advantages over the more traditional frequency-domain Turam type and downhole electromagnetic (DHEM) systems. Among such advantages are the use of a single receiver coil and the removal of noise due to free-space variations in transmitter-receiver geometry. The latter is important for DHEM surveys. In terms of field procedures and quantities measured, the system is similar to time-domain methods. 相似文献
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The inductive transient electromagnetic method (TEM) shows good potential for the detection of metallic relics of historical interest, such as buried antique bells, Buddhist idols, or precious metal nuggets. The effectiveness of the method was investigated with analogue models, using transmitter-receiver loop configurations with sizes or receiver spacings slightly different from those usually applied in earth resources exploration with the Sirotem system. The analogue modelling results show that the location and depth of the buried treasure may be obtained from the Sirotem data. A solid metallic object such as an antique bell could be detected to a depth about 12 times greater than its size, and treasure consisting of separate metallic objects, such as gold nuggets, could be detected to a depth 5 times its linear dimensions with a transmitter current of ? 20 A. In scaling down the dimensions of a target, its conductivity should be increased in order to preserve the same TEM conditions found in the field. However, since the buried treasure consists of gold or copper objects, it is not possible to properly scale the conductivity. Hence, in the field, the depth detection limit is expected to be greater than that derived from analogue modelling. 相似文献
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固定翼时间域航空电磁探测系统在实际飞行测量过程中,发射线圈、接收线圈姿态和吊舱摆动状态不断变化,在测量数据中引入如发射磁矩方向、接收分量方向以及系统收发距等参数的误差,影响数据反演成像效果.本文基于固定翼时间域航空电磁正演理论,利用姿态变换,引入发射线圈、接收线圈双旋转矩阵;根据发射、接收线圈相对位置的几何关系,求得摆动格林张量;推导了任意姿态角度以及任意摆动角度情况下的固定翼航空电磁响应三分量计算表达式.通过层状大地模型的仿真计算,分别研究了发射、接收线圈各姿态以及吊舱摆动状态对航空电磁响应的影响,得出发射线圈、接收线圈俯仰旋转和吊舱同向摆动对系统电磁响应影响最强;仿真分析了实际测量中,三种角度同时存在情况下,航空电磁响应的定量变化规律.在此基础上,讨论了响应系数与大地电导率的关系,同时给出基于响应系数的固定翼航空电磁系统线圈姿态和摆动状态校正方法,准二维层状大地模型反演结果表明,校正后数据的反演精度提高了33.1%. 相似文献
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A first application of a marine inductive source electromagnetic configuration with remote electric dipole receivers: Palinuro Seamount,Tyrrhenian Sea 
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下载免费PDF全文 Roxana Safipour Sebastian Hölz Marion Jegen Andrei Swidinsky 《Geophysical Prospecting》2018,66(7):1415-1432
We study a new marine electromagnetic configuration that consists of a ship‐towed inductive source transmitter and a series of remote electric dipole receivers placed on the seafloor. The approach was tested at the Palinuro Seamount in the southern Tyrrhenian Sea, at a site where massive sulphide mineralization has been previously identified by shallow drilling. A 3D model of the Palinuro study area was created using bathymetry data, and forward modelling of the electric field diffusion was carried out using a finite volume method. These numerical results suggest that the remote receivers can theoretically detect a block of shallowly buried conductive material at up to ～100 m away when the transmitter is located directly above the target. We also compared the sensitivity of the method using either a horizontal loop transmitter or a vertical loop transmitter and found that when either transmitter is located directly above the mineralized zone, the vertical loop transmitter has sensitivity to the target at a farther distance than the horizontal loop transmitter in the broadside direction by a few tens of metres. Furthermore, the vertical loop transmitter is more effective at distinguishing the seafloor conductivity structure when the vertical separation between transmitter and receiver is large due to the bathymetry. As a horizontal transmitter is logistically easier to deploy, we conducted a first test of the method with a horizontal transmitter. Apparent conductivities are calculated from the electric field transients recorded at the remote receivers. The analysis indicates higher apparent seafloor conductivities when the transmitter is located near the mineralized zone. Forward modelling suggests that the best match to the apparent conductivity data is obtained when the mineralized zone is extended southward by 40 m beyond the zone of previous drilling. Our results demonstrate that the method adds value to the exploration and characterization of seafloor massive sulphide deposits. 相似文献
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The diffusion of electromagnetic fields is dependent not only on conductivity, but also on magnetic permeability, dielectric permittivity and polarizability, i.e. dispersive conductivity. The long‐offset transient electromagnetic (LOTEM) method is mainly used to determine the spatial distribution of conductivity in the subsurface. However, earlier work on loop‐loop TEM suggests that transient EM methods can also be affected by induced polarization (IP). Numerous 1D forward calculations were carried out to study the IP effect on LOTEM data, using the Cole‐Cole relaxation model to simulate the polarizability of the ground. Besides the polarizability of each layer, the IP effect depends on the LOTEM field set‐up and the spatial distribution of conductivity in the ground. In particular, near‐surface layers with high chargeabilities can significantly distort the late time transients of the electric field components in the vicinity of the transmitter. The influence of polarizable layers on the magnetic field components can be neglected under normal circumstances. In 1997 and 1999, LOTEM measurements were carried out at Mt. Vesuvius in Italy to explore the geological structure of the volcano. Sensitivity studies on the effect of polarizable layers suggest that high chargeabilities in connection with conductive layers at greater depths would result in a detectable distortion of the electric field transients. Although the simultaneous IP measurements revealed high chargeabilities in a near‐surface layer, no evidence of IP effects could be found in the measured LOTEM data. We conclude that the observed chargeabilities are local and that 3D effects are probably present in the data. Another aspect is the measurement of the system response, which is usually measured by placing a receiver very close to the transmitter. Therefore, large distortions can be expected if near‐surface polarizable layers exist. This was verified in practice by field measurements in an area with high chargeabilities in Longerich, Cologne. 相似文献
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从电偶源三维地电断面可控源电磁法的二次电场边值问题及其变分问题出发,采用任意六面体单元对研究区域进行剖分,并且在单元分析中同时对电导率及二次电场进行三线性插值,实现电导率分块连续变化情况下,基于二次场的可控源电磁三维有限元数值模拟.这个新的可控源电磁三维正演方法可以模拟实际勘探中地下任意形状及电性参数连续变化的复杂模型.理论模型的计算结果表明,均匀大地计算的视电阻率误差和相位误差分别为0.002%和0.0005°.分层连续变化模型的有限元计算结果表明,其与对应的分层均匀模型解析结果有明显差异.三维异常体组合模型以及倾斜异常体等复杂模型的有限元计算结果也有效地反映了异常形态. 相似文献
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G. Michael Hoversten Michael Commer Eldad Haber Christoph Schwarzbach 《Geophysical Prospecting》2015,63(6):1508-1526
As motivation for considering new electromagnetic techniques for hydraulic fracture monitoring, we develop a simple financial model for the net present value offered by geophysical characterization to reduce the error in stimulated reservoir volume calculations. This model shows that even a 5% improvement in stimulated reservoir volume for a 1 billion barrel (bbl.) field results in over 1 billion U.S. dollars (US$) in net present value over 24 years for US$100/bbl. oil and US$0.5 billion for US$50/bbl. oil. The application of conductivity upscaling, often used in electromagnetic modeling to reduce mesh size and thus simulation runtimes, is shown to be inaccurate for the high electrical contrasts needed to represent steel‐cased wells in the earth. Fine‐scale finite‐difference modeling with 12.22‐mm cells to capture the steel casing and fractures shows that the steel casing provides a direct current pathway to a created fracture that significantly enhances the response compared with neglecting the steel casing. We consider conductively enhanced proppant, such as coke‐breeze‐coated sand, and a highly saline brine solution to produce electrically conductive fractures. For a relatively small frac job at a depth of 3 km, involving 5,000 bbl. of slurry and a source midpoint to receiver separation of 50 m, the models show that the conductively enhanced proppant produces a 15% increase in the electric field strength (in‐line with the transmitter) in a 10‐Ωm background. In a 100‐Ωm background, the response due to the proppant increases to 213%. Replacing the conductive proppant by brine with a concentration of 100,000‐ppm NaCl, the field strength is increased by 23% in the 100‐Ωm background and by 2.3% in the 10‐Ωm background. All but the 100,000‐ppm NaCl brine in a 10‐Ωm background produce calculated fracture‐induced electric field increases that are significantly above 2%, a value that has been demonstrated to be observable in field measurements. 相似文献
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裂缝型储层的描述包括预测裂缝分布特征和识别裂隙充填物.依据等效介质理论计算的纵波速度随裂缝密度的增大而减小.正演地震记录显示,裂缝介质含气时反射振幅最大,且变化程度比含油或含水时大.叠前方位AVO反演所得的各向异性梯度Bani与裂缝密度成正比,可用于描述有效裂缝发育强度.对于不同的裂缝密度,各向异性梯度Bani与各向同性梯度Biso的比值I(1)fluid近似为常数,且对流体敏感.经裂缝纵横比和背景介质拉梅常数修正后,流体因子Ifluid既不随纵横比变化,又不受背景介质的影响,是裂缝型储层敏感的流体识别因子.在塔里木盆地塔北哈拉哈塘地区热瓦普区块碳酸盐岩储层裂缝发育区域,运用该参数在井点处的流体识别效果与钻井结果一致. 相似文献