大地电磁测深法中静态效应的反演研究及应用

发布时间：2018-03-09 08:58

本文选题：大地电磁测深　切入点：静态效应　出处：《吉林大学》2015年硕士论文　论文类型：学位论文

【摘要】：大地电磁测深法利用天然交变电磁场研究地球电性结构，不受高阻层屏蔽，，对低阻层分辨率高。无需人工建立场源，施工方便，成本低廉，勘探深度范围大，在能源、资源及深部地球物理勘探等领域得到了广泛的应用。大地电磁测深法中存在一个普遍问题是数据中存在静位移,亦即对数视电阻率-周期曲线相对于区域值有一个竖直方向上的平行移动。这些静位移是由于测点附近存在小规模，浅部导电性异常体。电荷在小于电磁场趋肤深度的近地表异常体上积累。这些积累电荷在观测电场区域值的基础上产生了一个持续到任意低频率的扰动。错误的移除这些局部失真会导致反演解释所要研究的深部目标体时出现错误。电磁测深法的数据解释和静态效应校正通常是分开处理的。对于同样的实测数据不同的静态校应校正方法可能会得到不同的静位移值，这样一来，先移除数据中的静位移再寻找一个拟合被处理过的数据的模型就存在一个风险，这个风险就是地电结构推断解释中出现的异常可能是由于特定的静位移选择引起的。反演的同时校正静态效应的方法则可避免这个风险。在一维情况下，对含有静位移的大地电磁测深数据做反演解释所获得的模型和基于未失真数据得到的模型可能有一致的结构，但视电阻率值和深度可能是错误的。在二维和三维情况下，每个测点静位移的量通常是不一样的，当试图解释含有静态效应的数据时可能会导致所获得的模型中出现多余的结构。在一些特殊情况下，甚至找不到拟合数据的模型。为了移除多余的粗糙度，可以在每个点引进两个静位移参数用于缩放每个点TE和TM两种模式的视电阻率，但相位数据不受影响。Occam反演可以在获得最光滑模型的同时移除静态效应的影响。把静位移当作自由的参数参与到光滑模型反演中可以保证反演结果中出现的异常不只是由错误的静态效应校正引起的。本文在对当前中外相关文献收集和研读的基础上，对当前大地电磁测深资料处理中经常用到的静态效应校正手段进行研究。对所建立的一些理论模型进行了正演模拟，得出近地表局部不均匀体位于不同地电模型中时，两种模式(TE，TM)的响应特征。然后将静位移作为一个反演参数直接参与反演，在反演过程中同时校正由地表局部不均匀体引起的静态效应。结果表明，利用静态效应的直接反演法来校正静态效应可以获得不错的效果。最后，用静态效应的直接反演法处理了本溪-集安地区的实测大地电磁测深资料。有效的消除了实测数据中含有的静态效应，使得反演解释更加合理。
[Abstract]:The magnetotelluric sounding method uses natural alternating electromagnetic field to study the electrical structure of the earth, which is not shielded by the high resistivity layer, and has high resolution to the low resistivity layer. There is no need to establish the field source manually, the construction is convenient, the cost is low, the exploration depth range is large, and the exploration depth is in the energy source. Resources and deep geophysical exploration have been widely used. A common problem in magnetotelluric sounding is the existence of static displacement in the data. That is, the logarithmic apparent resistivity periodic curve has a vertical parallel movement relative to the regional value. These static displacements are due to the presence of small scales near the measured points. Shallow electrical conductivity anomaly. The charge accumulates on an anomaly near the surface that is smaller than the depth of the electromagnetic field. These accumulative charges produce a disturbance that persists to any low frequency on the basis of the observed electric field region. Removing these local distortions will lead to errors in the inversion interpretation of the deep object. Data interpretation and static effect correction of electromagnetic sounding methods are usually handled separately. Different static correction methods for the same measured data may result in different static displacement values. There is a risk of removing the static displacement from the data and then finding a model to fit the processed data. The risk is that the anomalies in the geoelectric structure inference interpretation may be caused by a particular static displacement selection, and this risk can be avoided by the method of inversion and correction of the static effect. In one dimensional case, the model derived from inversion interpretation of magnetotelluric sounding data with static displacement may have a consistent structure with the model based on undistorted data. But the apparent resistivity and depth can be wrong. In two and three dimensions, the amount of static displacement at each measuring point is usually different. When trying to interpret data with static effects, it may lead to redundant structures in the obtained model. In some special cases, no model can even be found to fit the data. In order to remove the excess roughness, Two static displacement parameters can be introduced at each point to scale the apparent resistivity of the te and TM modes at each point, But the phase data is unaffected. Occam inversion can remove the static effect while obtaining the smoothest model. Taking static displacement as a free parameter to participate in the smooth model inversion can ensure the anomalies in the inversion results. It is not just caused by incorrect static effect correction. In this paper, on the basis of the collection and study of the relevant literature at home and abroad, the static effect correction methods used frequently in the processing of magnetotelluric sounding data are studied, and the forward modeling of some theoretical models is carried out. The response characteristics of the two models in different geoelectric models are obtained, and the static displacement is taken as an inversion parameter to directly participate in the inversion. In the process of inversion, the static effects caused by local inhomogeneous bodies on the surface are corrected at the same time. The results show that the direct inversion method of static effects can get good results. Finally, the direct inversion method of static effect is used to deal with the measured magnetotelluric sounding data in Benxi-Ji'an area, which effectively eliminates the static effect in the measured data and makes the inversion interpretation more reasonable.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P631.325

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