Geophysical Explorations for Deep Subsurface Structures

Abstract

(1) For seismic reflection method, we have made a study of noise in the area where the noise, what is called ground roll, is quite dominant. As the results, it becomes possible for us to clarify the subsurface structures up to around 4, 000 meters by controling the above noise with use of a well designed T-offset, in-line-offset, etc., because the noise was still more dominant than signal even by applying conventional pattern shooting, group setting of geophones and CDP (common depth point).
(2) The practical applications of analog data processing system and Laser Scan to seismic exploration have given us a good support to interpret the deep and the complicated subsurface structures, and synthesized seismogram made from sonic log has improved our interpretative techniques to grasp the state of oil reservoir, As we also have recently been introducing the digital techniques into our seismic exploration system, we are to some extent able to solve such hard problems as attenuations of water reverberation and other noises which require quite elaborate processes based on deconvolution principles, and which however contribute much to grasp the deep subsurface structures.
(3) The application of electronic digital computer to the analytical routines of gravimetric or magnetic explorations has been to obtain good results as well. With the computer we have energetically put into practice to compute gravimetric basement from gravimetric anomaly map and to compose profile on gravimetric or magnetic basement from respective profile, which is, we believe, powerful means to synthetically interpret the deep subsurface structures together with the informations from seismic explorations and from wells.