井孔中多极源在分层介质中的声场模拟方法

Simulations of multipole acoustic waves in a borehole surrounded by layered media

水平分层地层是常见的地质模型,为了解声波在其中的传播规律,需要对该模型进行数值模拟,通常采用时域有限差分方法。然而对于地下数百米井段,如何提高计算效率,是必须考虑的问题。本文提出了一种可以动态获取计算区域的方法,保证在模拟结果可靠的情况下计算区域最小,并通过算例验证该方法的有效性。当发射器位于接收器下方,并且距离仪器下方最近的分层边界超过2.0 m时,位于仪器下方的所有分层介质可以在计算中忽略不计。对于位于阵列接收器上方的分层边界也同样采用类似的策略。本文利用该方法模拟了多层介质中单偶极声波测井响应,从中提取的纵横波速度与介质参数一致。

Horizontal layered formation is a common geological model, to obtain the response of acoustic logging in this media, we need to use the numerical simulation such as finite difference time domain. However,it is necessary to consider the strategy to solve the simulation of the sound field of the hundreds of meters underground, how to improve the calculation speed has to be considered. In this paper, we propose a simulation method for dynamic computing region, and give the optimization scheme of the region selection, and the effectiveness of the method is verified by numerical examples. It is shown that when the source is more than 2.0 m above from the nearest bed boundary, all layers beneath the logging tool can usually be ignored in the computation. The layers above the last receiver should be treated similarly. Two numerical examples, for monopole and dipole logging respectively, are presented to validate the developed program.