对3种典型检波器及其数据的几点看法

Discussions on three typical seismic sensors and their data

动圈式检波器与压电式检波器是当前石油地震勘探中应用最为广泛的两类检波器,典型代表包括动圈式速度检波器、水中压电式压力检波器以及陆上压电式加速度检波器。分析了3种检波器的物理结构、力学模型、等效电路以及传输函数,实际数据证明动圈式检波器拾取的地表振动速度与陆地压电检波器拾取的地表振动加速度在主要频带内是等效的,但后者一致性稍差。水中压电式检波器(简称水检)是压力型检波器,不是加速度型检波器,其与动圈式速度检波器或者MEMS加速度检波器(简称陆检)是组成双检海底电缆(OBC)与海底节点(OBN)施工、采用双检合并技术消除水层鸣震的装备基础。当前双检合并技术的几个假设前提,如地震波场是平面波场,检波器距离海底非常近但二者并不接触,不考虑耦合效应,不考虑检波系统的机电效应等,在实际生产中并不满足。因此,提高双检合并技术的实用性需要对以上假设条件进行更深入的研究并采取相应的工程措施。考虑到检波器的主要功能是“忠实地记录大地振动”,野外经由电路提频的做法不应提倡。此外,对比了容易混淆的两种检波器分类方法并清晰地展示了检波器的分类标准及其对数据的影响。

Moving coil geophone and piezoelectric sensor(including piezoelectric pressure hydrophones used in water and piezoelectric accelerometers used on land,LP)are the two most widely employed types of sensors in geophysical prospecting.A table consisting of the physical structures,mathematical models,and transfer functions of these two sensor types is established for comparison.Theoretical analysis and field experiment data showed that the velocity measured by moving coil geophone and the acceleration by LP accelerometer are equivalent across the major frequency bands in terms of representing ground movement.Regarding hydrophone,it is essential to understand that it is pressure-type detector,not an accelerometer.Based on the fundamentals of seismic wave dynamics and practical application,output of pressure-type hydrophone is proportional to the velocity of water particles for the up-going wave field and a-180°phase difference is exhibited for the down-going wave field.This relationship forms the basic principles for dual-sensor summation technology.This technology relies on several assumptions,such as a plane wave field,the sensor being very close to the seafloor but without direct contact(avoiding sensor-ground coupling effects),and without involvement of the sensing system.The author questions these assumptions and argues that more effective attenuation of water column reverberation by this technology requires additional efforts theoretically,experimentally and operationally.Meanwhile,the main function of sensor is simply to follow the movement of the ground faithfully,circuit-based enhancement of high frequencies in the field may reduce the S/N ratio and resolution and should not be promoted.Finally,the classification of sensors based on different standards has been clarified,contributing to a more thorough understanding of the nature of sensors and also its output data.