井—地瞬变电磁法浮动系数空间交汇与等效电流环反演方法研究

发布时间：2018-05-20 01:03

本文选题：井-地瞬变电磁法 + 等效电流环　；参考：《中国地质大学》2017年博士论文

【摘要】：我国煤矿水文地质条件十分复杂,水害防治形势愈发严峻,水源性隐蔽致灾体的准确探测仍将是今后防治水工作的重点和难点。煤矿井下水害事故主要发生在巷道掘进期间和工作面回采期间。虽然物探方法在以往实践中提前发现灾害性地质异常体,为保障矿井安全生产发挥巨大作用,但也存在对巷道前方探测距离不够长(一般在100m左右)、假异常多,对工作面穿透距离短(一般不超过200m)、远处分辨率不够等缺点。另外,在回采工作面顶底板含水层进行注浆改造时,对小体积的导水性陷落柱、岩溶、断层等水源性隐蔽致灾体的精确探测存在技术缺口。针对当前技术手段的不足,研究一种在煤矿井下水平钻孔中接收感应二次场、地面回线磁源激发一次场的瞬变电磁探测技术(简称井-地瞬变电磁法)。地面发射源可将回线源和电流尽量加大,增加发射磁矩以尽量激发地下水源性隐蔽致灾体;水平钻孔内布置的测点距离异常体更近,最大限度减少二次场的距离损失。理论上,井-地瞬变电磁法对水源性隐蔽致灾体具有更强的分辨能力。在煤矿巷道掘进前方超前钻孔中应用该项技术,能实现利用单个钻孔长距离准确探查掘进前方水源性隐蔽致灾体的目的;在工作面钻孔中应用该项技术,能对钻孔周围漏掉的水源性隐蔽致灾体进行定位,提高探查准确度和效率。论文以载流回线磁源激发场分布和异常体感应涡流场三分量特征为研究对象,以公式推导、三维时域有限差分数值模拟、理论分析等为研究方法,对异常体的井-地瞬变电磁法响应特征、感应涡流场三分量的空间指向性、浮动系数空间交汇算法和最小二乘反演算法进行研究,实现基于井-地瞬变电磁法的异常体三维空间定位技术。论文取得的主要研究成果如下:(1)推导了激发场的解析解公式,获得了激发场的分布特征和回线源最佳尺寸匹配依据。从毕奥-萨伐尔定律出发,对圆形回线源、长方形回线源和正方形回线源分别进行磁感应强度解析解的推导。对各种激发源载入直流电后在空间形成的磁场分布进行数值计算,分析总结其分布特征。依据回线源在地下不同深度产生磁场的强度分布特征,获得最佳回线源尺寸的选择办法。三种激发源的激发场在空间的分布特征基本一致,激发场强度总体呈浅部强、深部弱的分布特征,磁感应强度主要受与回线源的距离控制,在回线附近的磁场表现为最强值。随着与回线源之间距离的增加,磁感应强度变化逐渐减慢。在与回线源一定距离的平面上,磁感应强度分布呈中间强、边缘弱的特征,等值线依据回线源形状表现为圆形或椭圆形。在回线源中间部分区域,激发场主要为垂向磁场且强度在横向上的变化较小,这是地面瞬变电磁法将回线中心一定区域当作均匀场的原因。以实际生产中常用的正方形回线为例,计算8种常见尺寸回线在地下不同深度产生的磁场。大尺寸回线源在浅部产生的激发场并非更强,但随深度变化相对稳定,且深部的激发场相对更强。在某个固定深度的目标体处,过大或过小尺寸的回线源并不能激发出最大强度的一次磁场。计算结果对井-地瞬变电磁法回线源尺寸的选择具有指导意义。(2)获得了煤矿典型水源性隐蔽致灾体的响应特征,和主要参数改变对三分量响应的影响规律。采用三维时域有限差分算法,对构建的含水陷落柱、小煤窑积水采空区、含导水断层和顶板砂岩富水体等煤矿典型水源性隐蔽致灾体的全空间三分量响应进行数值模拟。各模型的异常体均有明显的三分量磁异常响应,异常测道曲线均以“N”或“V”为基本形状,过零点和极值点分别指向异常体中心在测线上的位置。对回线源尺寸、低阻覆盖层、异常体方位、异常体规模和距离这五方面因素的影响进行数值模拟。回线源尺寸的增加能提高总场和异常场的响应强度,但增加幅度逐渐减弱,且异常场面临幅值极限。低阻覆盖层使得异常响应幅值随覆盖层电阻率的降低而减弱。三分量异常曲线形态组合与异常体相对测线的空间方位具有单一的匹配性,可据此对异常体方位进行判断。异常体与测线距离的变化,只改变异常曲线的幅值,不改变曲线的形态。距离测线越远,异常信号越弱。以仪器精度和大地电磁噪声为基本阈值,确定可分辨最小信号强度。从测线深度改变时总场三个分量的强度与最小信号阈值之间的相对关系,探讨了井-地瞬变电磁法的极限探测深度。(3)以水平电流环辐射磁场各分量矢量的空间指向性为基础,开发出适用于水平测线不同Y偏移距的浮动系数空间交汇算法。通过分析水平电流环辐射磁场的三个分量在XY平面、XZ平面上,水平测线处各测点的三分量矢量分布,确定各分量矢量与电流环中心在XY平面、XZ平面上具有明确的指向性。采用时域有限差分算法模拟异常体的异常场,分析感应涡流磁场随时间的分布规律,通过与水平电流环产生磁场的进行对比,认为异常体在外部产生的异常场,可以用位于异常体内部的电流环所辐射的磁场来代替。研究水平测线上磁场三分量矢量对水平电流环中心的交汇特性,开发出适用于水平测线的浮动系数空间交汇算法,并建立基于不同Y偏移距的浮动系数表。在进行XZ平面交汇时,根据系数表对Z分量进行自适应调节,可使XZ平面的交汇结果更准确。分别位于水平测线不同象限四个模型的试算结果,验证了浮动系数空间交汇算法的准确性。采用此算法对不同倾斜角度的近似水平电流环进行空间定位试算,计算结果说明浮动系数空间交汇算法更适用于水平电流环,倾斜角度的增加会导致交汇准确度的降低。(4)以分离的异常场三分量数据为基础,采用基于电流环理论的最小二乘算法,反演异常体的尺寸、空间姿态和中心坐标。以水平测线正常区段采集的数据为背景场,采用多项式拟合算法对测线异常段的背景场进行曲线拟合,获得全测线的背景场。通过总场数据减去背景场的方式得到异常场。借助三维直角坐标系的旋转公式实现任意倾斜角度的电流环正演。视异常体内部的涡流场为一个等效电流环,赋予其中心点坐标、半径、倾斜角度等变量,使用带约束的最小二乘反演算法对各变量进行反演计算,以最小拟合误差为导向对电流环的参数不断迭代计算,获得异常体中心坐标、空间姿态、规模大小等参数。分别以MAXWELL软件对板状体的正演、时域有限差分算法对立方体的数值模拟、以地面铝板为异常体的现场试验,共三种方式取得的数据为基础,对反演算法进行验证。结果显示,对板状体数据反演得到的电流环中心坐标、空间姿态、尺寸均与模型参数吻合;对立方体数据反演得到的电流环中心坐标和空间姿态与模型参数吻合较好,但尺寸结果不稳定,与模型参数存在一定偏差;对现场试验数据反演得到的电流环中心坐标和空间姿态与模型参数吻合较好,但同样存在尺寸结果不稳定,存在一定偏差的现象。
[Abstract]:The hydrogeological conditions of coal mines in China are very complicated and the prevention and control of water hazards are becoming more and more severe. The accurate detection of the hidden source of water source will still be the key and difficult point in the future work of water prevention and control. The abnormal geological body plays a great role in ensuring the safety of mine production, but there are also shortcomings in the distance not long (usually around 100m), false abnormality, short penetration distance (generally not more than 200m), and not enough resolution in the distance in the front of the roadway. In addition, when the aquifer in the roof and floor of the mining face is modified, it is small There is a technical gap in the precise detection of water borne concealment bodies, such as the volume of water diversion column, karst, fault and so on. In view of the shortage of current technical means, a transient electromagnetic detection technique (called well ground transient electromagnetic method) for receiving the first field in the horizontal borehole in the underground coal mine is studied. The source and current can be used to increase the source and current of the return line as far as possible, to increase the emission magnetic moment to try to stimulate the underground water source hidden disaster relief body as far as possible; the measurement points arranged in the horizontal borehole are closer to the abnormal body, and the distance loss of the two field is reduced to the maximum. This technique can be applied in the front of the advance borehole in the front of the mine roadway, and it can realize the purpose of using the long distance of a single drill to detect the waterborne concealment body in front of the heading, and the application of this technique in the drilling of the working face can make the location of the waterborne concealment body leaked around the borehole, and improve the accuracy and efficiency of the exploration. The three component characteristics of the excitation field distribution of the loop magnetic source and the abnormal body induction eddy current field are studied. By formula derivation, the three-dimensional finite difference numerical simulation and the theoretical analysis are used as the research methods. The response characteristics of the well to ground transient electromagnetic method, the spatial directivity of the three components of the induced eddy current field, the spatial intersection algorithm of the floating coefficient and the most The small two ply inversion algorithm is studied to realize the three-dimensional spatial positioning technique of abnormal body based on well ground transient electromagnetic method. The main achievements of this paper are as follows: (1) the analytical formula of the excitation field is derived, the distribution characteristics of the excitation field and the best size matching basis for the return line source are obtained. The linear source, the rectangular return source and the square loop source are derived for the analytical solution of the magnetic induction intensity respectively. The distribution characteristics of the magnetic field in the space formed after the various excitation sources are loaded in the space are calculated, and the distribution characteristics of the magnetic field are analyzed and summed up. The intensity distribution characteristics of the magnetic field are generated by the source of the return line at different depths in the underground, and the optimum return line ruler is obtained. The distribution characteristics of the excitation field of the three excitation sources are basically the same, the intensity of the excitation field is shallow and the deep is weak, the magnetic induction intensity is mainly controlled by the distance from the return line, and the magnetic field near the return line is the strongest. With the increase of the distance between the return line and the return line, the magnetic induction intensity changes In a plane with a certain distance from the return line source, the distribution of magnetic induction intensity is strong in the middle and weak in the edge, and the contour lines are round or elliptical according to the shape of the return line. In the middle part of the loop source, the excitation field is mainly the vertical magnetic field and the intensity is slightly changed in the transverse direction. This is the ground transient electromagnetic method which is the return line. The cause of a certain area of the center is considered as a uniform field. Taking the square return line commonly used in actual production as an example, the magnetic field produced at different depths of the 8 common dimensions is calculated. The excitation field produced in the shallow part is not stronger, but it is relatively stable with the depth change, and the deep excitation field is relatively stronger. The maximum intensity of the primary magnetic field can not be excited by the large or too small return line source at the target body of the degree. The calculation results are of guiding significance to the selection of the source size of the well ground transient electromagnetic method. (2) the response characteristics of the typical waterborne hidden disaster body in the coal mine are obtained, and the influence of the main parameters on the response of the three component is changed. The three dimensional finite difference time domain method is used to simulate the full space three component response of the constructed water bearing collapse column, the small coal mine water gob area, the water diversion fault and the roof sandstone rich water body. All the abnormal bodies of each model have an obvious three component magnetic anomaly response, and the abnormal path curves are all "N" or "V" is the basic shape, the zero crossing point and the extreme point point to the location of the anomaly body center on the measuring line respectively. Numerical simulation is carried out on the influence of the five factors such as the line source size, the low resistance cover layer, the abnormal body azimuth, the abnormal body size and the distance. The increase of the return line source size can increase the response strength of the total field and the abnormal field, but increase the response strength of the total field and the abnormal field. The amplitude of the abnormal response decreases with the decrease of the resistivity of the overlay. The combination of the three component abnormal curve and the spatial orientation of the abnormal body has a single match, which can be used to judge the azimuth of the abnormal body and the variation of the distance between the abnormal body and the line measuring. It only changes the amplitude of the abnormal curve and does not change the shape of the curve. The farther the distance from the measuring line, the weaker the abnormal signal is. The relative relation between the intensity of the three components of the total field and the minimum signal threshold is determined by using the instrument precision and the magnetotelluric noise as the basic threshold. The relationship between the intensity of the total field and the minimum signal threshold is discussed. The limit detection depth of the variable electromagnetic method. (3) based on the spatial directivity of each component vector of the magnetic field of the horizontal current ring, a floating coefficient space intersection algorithm suitable for the different Y offset of the horizontal line is developed. By analyzing the three components of the radiation magnetic field of the horizontal current ring in the XY plane, the XZ plane, and the three measuring points at the horizontal line. The component vector distribution is determined by the definite directivity of each component vector and the center of the current loop in the XY plane and the XZ plane. The time domain finite difference method is used to simulate the anomalous field of the abnormal body and analyze the distribution of the eddy current magnetic field with the time. The anomalous field can be replaced by the magnetic field radiated by the current ring located in the abnormal body. To study the intersection characteristic of the three component vector to the center of the horizontal current loop, a floating coefficient space intersection algorithm suitable for the horizontal line is developed and the floating coefficient table based on the different Y offset is established. The intersection of the XZ plane is confluence. On the basis of the adaptive adjustment of the Z component according to the coefficient table, the intersection results of the XZ plane are more accurate. The accuracy of the floating coefficient space intersection algorithm is verified by the trial results of four models of the different quadrants of the horizontal line. The algorithm is used to calculate the spatial location of the near horizontal current ring with different inclined angles. The result shows that the spatial intersection algorithm of floating coefficient is more applicable to the horizontal current ring, and the increase of the inclination angle will lead to the reduction of intersection accuracy. (4) based on the three component data of the separated anomaly field, using the least square algorithm based on the current loop theory, the scale of the abnormal body, the spatial attitude and the central coordinate are retrieved, and the horizontal line is normal. The data collected in the section is the background field, and the background field of the anomaly segment is fitted by polynomial fitting algorithm. The background field of the full measuring line is obtained. The anomalous field is obtained by the total field data subtracting the background field. With the help of the rotation formula of the 3D rectangular coordinate system, the current loop of the arbitrary angle angle is realized. The interior of the apparent anomaly body is realized. The eddy current field is an equivalent current ring, which gives its center point coordinates, radius and angle of angle, and uses the least square inversion algorithm with constraint to calculate the variables. The parameters of the center coordinate, space attitude and size of the anomaly body are obtained by iterative calculation of the parameters of the current ring with the minimum fitting error as the guidance. The numerical simulation of the cube by MAXWELL software, the numerical simulation of the cube by the finite difference time domain algorithm, the field test of the ground aluminum plate as the abnormal body, the data obtained from three ways, and the verification of the inversion algorithm. The results show that the center coordinates of the current ring, the spatial attitude and the size are all obtained by the inversion of the plate data. The center coordinates and the spatial attitude of the current loop obtained by the inversion of the cube data are in good agreement with the model parameters, but the size results are not stable, and there is a certain deviation from the model parameters. The center coordinates and the spatial attitude of the current loop obtained from the field test data are in good agreement with the model parameters, but the size of the current loop is also in good agreement with the model parameters. The result is unstable and there is a certain deviation.
【学位授予单位】：中国地质大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TD745;P631.325

【相似文献】