可控源電場數(shù)據(jù)三維反演及應(yīng)用
發(fā)布時間：2018-08-31 13:10
【摘要】：可控源音頻大地電磁測深法(CSAMT)自上世紀(jì)七、八十年代問世以來，已經(jīng)發(fā)展成為一種重要的電磁法勘探手段�，F(xiàn)在，可控源方法的一維、二維的正反演研究已日趨成熟，三維正反演研究也已有了長足的進(jìn)步。常用的正演算法有有限差分法、有限元法和積分方程法，反演方法有共軛梯度法、非線性共軛梯度法、牛頓法、擬牛頓法等。但由于計(jì)算量非常大，占用內(nèi)存空間多等的限制，距離實(shí)際應(yīng)用還有一定距離。因此本文期望在現(xiàn)有的技術(shù)的基礎(chǔ)上，考慮反演過程中如何選擇初始模型和頻率，期望通過大量的數(shù)值模擬，提出在滿足①節(jié)約計(jì)算量②提高反演速度③不犧牲反演效果的條件下，可控源實(shí)際應(yīng)用的一種解決方案，實(shí)現(xiàn)高效的三維實(shí)際數(shù)據(jù)反演。 首先，正演理論上我們借鑒了Commer等的思路，將有限長導(dǎo)線源激發(fā)的總電場，分解為由層狀介質(zhì)電阻率產(chǎn)生的背景場和三維異常體產(chǎn)生的異常場。背景場計(jì)算采用虛界面法，數(shù)值計(jì)算上用直接積分法。異常場計(jì)算采用的是交錯網(wǎng)格有限差分法。反演方面，本文利用了擬牛頓法中的一種，有限內(nèi)存（L-BFGS）法。它具有擬牛頓法不需要存儲大型海森矩陣或它的逆矩陣的優(yōu)點(diǎn)，同時在擬牛頓法的基礎(chǔ)上做了改進(jìn)，給定一個正整數(shù)m，只需存儲前面m次的迭代信息，大大減少了計(jì)算時占用的內(nèi)存空間，從而提高了計(jì)算速度。 然后，設(shè)計(jì)一個兩層介質(zhì)的模型，通過正演計(jì)算模型的響應(yīng)，對模型響應(yīng)施加固定誤差作為觀測數(shù)據(jù)參與反演。反演過程中，改變初始模型、網(wǎng)格大小和頻率，對比分析反演結(jié)果發(fā)現(xiàn)，因?yàn)長-BFGS法是在適當(dāng)?shù)臈l件下具有全局收斂性，所以初始模型如何選擇對于反演結(jié)果影響很大。為了提高反演的效率和準(zhǔn)確性，本次研究通過粗網(wǎng)格全頻率反演結(jié)果設(shè)計(jì)了反演的初始模型。再根據(jù)要反演的異常深度，計(jì)算關(guān)鍵頻率，采用精細(xì)網(wǎng)格部分頻率反演，得到準(zhǔn)確的反演結(jié)果。 最后，本文對理論模型中提出的反演方案對實(shí)際數(shù)據(jù)進(jìn)行了反演驗(yàn)證。根據(jù)粗網(wǎng)格全頻率反演結(jié)果設(shè)計(jì)初始模型。根據(jù)實(shí)際需要選擇反演頻率，在最佳頻率的基礎(chǔ)上，加入了高頻、低頻和高頻低頻的組合，來控制上下出現(xiàn)的虛假異常，對比分析尋找反演的最佳頻率組合。反演結(jié)果與地質(zhì)資料和其他地球物理方法結(jié)果吻合較好，說明了這種反演方案的可行性。 本文通過理論模型和實(shí)際數(shù)據(jù)的反演研究得出以下結(jié)論：1、提出了一種可行性的反演方案，首先根據(jù)粗網(wǎng)格全頻率反演結(jié)果設(shè)計(jì)初始模型，然后由探測深度公式求得關(guān)鍵頻率，加入高頻和低頻，初始模型選精細(xì)網(wǎng)格在進(jìn)行一次反演。這種方案既節(jié)約了計(jì)算時間，又保證了反演的準(zhǔn)確性。2、反演計(jì)算在選擇初始模型時，初始模型電阻率如果低于實(shí)際模型電阻率，反演結(jié)果較難擬合，反演的電阻率較低。初始模型電阻率高于實(shí)際模型電阻率則能更接近于理論模型。3、三維反演過程中頻率的個數(shù)不是越多越好，需要通過計(jì)算來求得關(guān)鍵頻率，再引入高頻和低頻進(jìn)行控制，，反演結(jié)果更為準(zhǔn)確。4、電場Ex分量反演，在x方向上控制較好，y方向上有延伸。
[Abstract]:Controlled Source Audio Magnetotelluric Sounding (CSAMT) has become an important means of electromagnetic exploration since it came out in the 1970s and 1980s. Now, one-dimensional and two-dimensional forward and inversion research of CSAMT has become more and more mature, and three-dimensional forward and inversion research has made considerable progress. The finite element method and the integral equation method, the inversion method has the conjugate gradient method, the nonlinear conjugate gradient method, the Newton method, the quasi-Newton method and so on. But because the computation quantity is very big, occupies the memory space many and so on the restriction, still has certain distance from the practical application. Initial model and frequency are expected to be simulated by a large number of numerical simulations, and a practical solution of controllable source inversion is proposed to realize efficient 3D real data inversion without sacrificing the inversion effect.
Firstly, we use Commer's method for reference, and decompose the total electric field excited by the finite-length wire source into the background field generated by the resistivity of layered medium and the anomalous field generated by three-dimensional anomalous body. In the inversion aspect, this paper uses one of the quasi-Newton methods, the finite memory (L-BFGS) method. It has the advantage that the quasi-Newton method does not need to store the large Heisen matrix or its inverse matrix. At the same time, it is improved on the basis of the quasi-Newton method. Given a positive integer m, it only needs to store the iterative information of the previous m times, which greatly reduces the calculation. The memory space is occupied, thus improving the computation speed.
Then, a two-layer medium model is designed, and a fixed error is applied to the model response as the observed data through forward calculation. During the inversion process, the initial model, mesh size and frequency are changed. The inversion results show that L-BFGS method has global convergence under appropriate conditions, so the initial inversion is carried out. In order to improve the efficiency and accuracy of inversion, an initial inversion model is designed based on the full-frequency inversion results of coarse grids. Then the key frequency is calculated according to the anomaly depth to be inverted, and the accurate inversion results are obtained by partial frequency inversion of fine grids.
Finally, the inversion scheme proposed in the theoretical model is used to validate the actual data. The initial model is designed according to the full-frequency inversion results of the coarse grid. The inversion frequency is selected according to the actual needs. On the basis of the optimal frequency, the combination of high frequency, low frequency and high frequency low frequency is added to control the false anomalies, and the comparison is made. The inversion results are in good agreement with geological data and other geophysical methods, which shows the feasibility of this inversion scheme.
In this paper, the following conclusions are drawn through the inversion of theoretical model and actual data: 1. A feasible inversion scheme is proposed. First, the initial model is designed according to the full-frequency inversion result of coarse mesh, then the key frequency is obtained by the formula of detection depth, and the high and low frequencies are added to the initial model, and the fine mesh is selected for one inversion. This scheme not only saves calculation time, but also ensures the accuracy of inversion. 2. When selecting the initial model, if the initial model resistivity is lower than the actual model resistivity, the inversion result is more difficult to fit, and the inversion resistivity is lower. In the process of the inversion, the number of frequencies is not the more, the better. It is necessary to calculate the key frequencies, and then introduce high and low frequencies to control the inversion. 4. The inversion results of Ex component of electric field are more accurate.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：P631.325
本文編號：2215083
[Abstract]:Controlled Source Audio Magnetotelluric Sounding (CSAMT) has become an important means of electromagnetic exploration since it came out in the 1970s and 1980s. Now, one-dimensional and two-dimensional forward and inversion research of CSAMT has become more and more mature, and three-dimensional forward and inversion research has made considerable progress. The finite element method and the integral equation method, the inversion method has the conjugate gradient method, the nonlinear conjugate gradient method, the Newton method, the quasi-Newton method and so on. But because the computation quantity is very big, occupies the memory space many and so on the restriction, still has certain distance from the practical application. Initial model and frequency are expected to be simulated by a large number of numerical simulations, and a practical solution of controllable source inversion is proposed to realize efficient 3D real data inversion without sacrificing the inversion effect.
Firstly, we use Commer's method for reference, and decompose the total electric field excited by the finite-length wire source into the background field generated by the resistivity of layered medium and the anomalous field generated by three-dimensional anomalous body. In the inversion aspect, this paper uses one of the quasi-Newton methods, the finite memory (L-BFGS) method. It has the advantage that the quasi-Newton method does not need to store the large Heisen matrix or its inverse matrix. At the same time, it is improved on the basis of the quasi-Newton method. Given a positive integer m, it only needs to store the iterative information of the previous m times, which greatly reduces the calculation. The memory space is occupied, thus improving the computation speed.
Then, a two-layer medium model is designed, and a fixed error is applied to the model response as the observed data through forward calculation. During the inversion process, the initial model, mesh size and frequency are changed. The inversion results show that L-BFGS method has global convergence under appropriate conditions, so the initial inversion is carried out. In order to improve the efficiency and accuracy of inversion, an initial inversion model is designed based on the full-frequency inversion results of coarse grids. Then the key frequency is calculated according to the anomaly depth to be inverted, and the accurate inversion results are obtained by partial frequency inversion of fine grids.
Finally, the inversion scheme proposed in the theoretical model is used to validate the actual data. The initial model is designed according to the full-frequency inversion results of the coarse grid. The inversion frequency is selected according to the actual needs. On the basis of the optimal frequency, the combination of high frequency, low frequency and high frequency low frequency is added to control the false anomalies, and the comparison is made. The inversion results are in good agreement with geological data and other geophysical methods, which shows the feasibility of this inversion scheme.
In this paper, the following conclusions are drawn through the inversion of theoretical model and actual data: 1. A feasible inversion scheme is proposed. First, the initial model is designed according to the full-frequency inversion result of coarse mesh, then the key frequency is obtained by the formula of detection depth, and the high and low frequencies are added to the initial model, and the fine mesh is selected for one inversion. This scheme not only saves calculation time, but also ensures the accuracy of inversion. 2. When selecting the initial model, if the initial model resistivity is lower than the actual model resistivity, the inversion result is more difficult to fit, and the inversion resistivity is lower. In the process of the inversion, the number of frequencies is not the more, the better. It is necessary to calculate the key frequencies, and then introduce high and low frequencies to control the inversion. 4. The inversion results of Ex component of electric field are more accurate.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：P631.325
【參考文獻(xiàn)】
相關(guān)期刊論文 前7條
1 林昌洪;譚捍東;舒晴;佟拓;張玉玫;;稀疏測線大地電磁資料三維反演研究:合成算例(英文)[J];Applied Geophysics;2012年01期
2 楊建國;翟金元;楊宏武;王小紅;謝春林;王興安;任秉琛;;甘肅花牛山噴流沉積型金銀鉛鋅礦床控礦因素與找礦前景分析[J];大地構(gòu)造與成礦學(xué);2010年02期
3 林昌洪;譚捍東;佟拓;;利用大地電磁三維反演方法獲得二維剖面附近三維電阻率結(jié)構(gòu)的可行性[J];地球物理學(xué)報(bào);2011年01期
4 劉云鶴;殷長春;;三維頻率域航空電磁反演研究[J];地球物理學(xué)報(bào);2013年12期
5 代文軍;;甘肅北山花牛山金銀鉛鋅礦床成因探討[J];華南地質(zhì)與礦產(chǎn);2010年03期
6 胡祖志,胡祥云,何展翔;三維大地電磁數(shù)據(jù)的二維反演解釋[J];石油地球物理勘探;2005年03期
7 翁愛華,王雪秋;利用數(shù)值積分提高一維模型電偶源電磁測深響應(yīng)計(jì)算精度[J];西北地震學(xué)報(bào);2003年03期
相關(guān)博士學(xué)位論文 前1條
1 劉云鶴;三維可控源電磁法非線性共軛梯度反演研究[D];吉林大學(xué);2011年
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