含水溶洞的地面核磁共振响应数值模拟研究

Study of numerical simulation of SNMR response of water-filled cave

针对目前水平层状含水层的地面核磁共振响应特征已研究的比较透彻,而含水溶洞的响应特征却鲜有涉及的现状,本文给出含水溶洞地面核磁共振响应的计算方法.在文中,作者使用华军对双重Bessel函数无限积分的计算方法,实现了大回线源激发磁场的快速计算.再通过对地面核磁共振正演公式的离散化,实现了三维结构含水体的地面核磁共振正演计算.在此基础上,作者在柱坐标系下建立球形充水溶洞模型,针对其不同埋深情况,分别对其响应进行数值模拟,得到了球形充水溶洞模型的地面核磁共振响应.

The technology of surface nuclear magnetic resonance response on layered aquifer has been relatively mature. However the response of cave, which contains water, was rarely involved in professional articles. The method for calculating the surface nuclear magnetic resonance response of water-filled cave is given in this paper. Firstly, computation problem of excitation magnetic field, which is generated by a loop, and it＇s numeric expression contains two Bessel functions. It is solved by use of method of HuaJun. Calculated results show that the algorithm has high accuracy. Secondly, forward calculation of 3-D aquifer is achieved by way of discrete surface nuclear magnetic resonance forward formula. By comparing the results of two simple layer aquifer examples which respectively are calculated by this forward algorithm and NUMIS software. It proves that the algorithm can obtain approximate results. On that foundation, models of water-filled cave spherical cave are established in cylindrical coordinates, and surface nuclear magnetic resonance response of these models which are putted in different depths is calculated. Some laws of the response of water-filled cave are obtained. By comparing response characteristics between cave model and layer aquifer, the difference between the two is found that amplitude curve of a water-filled cave spherical cave have many crest but curve of a layered aquifer just have one.