Micro-logging near-surface absorption compensation software.
The relatively loose near-surface medium seriously absorbs and attenuates the energy of seismic signals, especially the energy of high-frequency signals, which greatly reduces the signal-to-noise ratio and resolution of seismic signals. In order to solve this problem, we developed the near-surface absorption compensation software using micro-logging data. Characterized in that micro logging records obtained from seismic sources with different depths are edited, the first break waves are reserved, the amplitude spectrum and the phase spectrum are analyzed, and the systematic filtering response of the depth corresponding to the first break wave at the minimum depth is obtained, and the systematic filtering response of the first break wave at the minimum depth is taken as the expected output, and the filtered responses of the first break waves with different depths are obtained according to the least square inverse filtering principle, and after acting on the ground seismic data, the near-surface absorption attenuation of the ground seismic data is realized.
Figure 1 shows the comparison of stacked profiles before and after absorption compensation. It can be seen that the high-frequency components of seismic signals on the processed profile are obviously increased, and the information content is obviously increased. Many details are reflected, and some interference complex waves are separated. Fig. 2 is the spectrum analysis result of seismic exploration target layer in Figure 1. It can be seen that high-frequency compensation broadens the bandwidth of dominant signal-to-noise ratio before processing from 0~70Hz to 0~85Hz, and the high-frequency energy is strengthened, while the low-frequency components are basically unchanged, thus greatly improving the resolution of seismic signals.
Fig. 1 comparison of superimposed profiles before (left) and after (right) surface absorption compensation
Fig. 2 amplitude spectrum comparison of superimposed data before and after surface absorption compensation.
The software was developed by Zhejiang University and provided by Zhejiang University. At present, the products are mainly used in desert areas and soil-covered areas, and have been tested and applied in many different surface areas in China, belonging to mature software. A method for high-frequency compensation of seismic signals by micro-logging, patent number: ZL2005 10049340.4, patent authorization date: August 20, 2008.
Dedicated coupling detector and matching processing software
It is difficult for the conventional iron-pointed tail cone of geophone to be perfectly coupled with the loose surface medium in desert area, which causes serious energy loss and waveform distortion in the transmission process of geophone coupling system, especially the high-frequency component is greatly weakened, thus reducing the resolution of seismic data. Therefore, we have developed a special coupling device (Figure 3), and on this basis, we have developed a special coupling matching processing software. It is characterized in that cylindrical geophone bases with different concrete ratios are designed according to the parameters of P-wave velocity, density and surface thickness of the surface medium in the work area to replace the geophone tail cone with poor coupling with the surface. The wave impedance of the geophone base will be between the surface wave impedance and the wave impedance of the geophone core with different specific proportions. At the same time, in order to increase the reception of high-frequency signal components, the cylindrical size of the geophone base should match the dynamic characteristics of the topsoil medium, so as to reduce the scattering energy loss and achieve the best coupling with the surface medium. In the same buried position and under the same excitation conditions (Figure 4), the concrete base geophone and the conventional iron tail cone geophone with the same large line arrangement are observed on adjacent tracks to obtain comparable seismic records. The concrete geophone records obtained under the same conditions are regarded as the expected output of the conventional geophone records with iron tail cone, and the optimal Wiener filtering principle is used. The optimal coupling matched filter factor is obtained, and then the seismic records obtained by all conventional coupled detectors are matched and filtered, so that the signals obtained by all detectors are equivalent to the optimal coupling received signals.
Fig. 3 Heterocoupling detector
Fig. 4 Schematic diagram of field observation mode of special coupled geophone.
Fig. 5 Comparison of front (left) and rear (right) overlapping contours of special coupling matching.
Fig. 6 spectrum comparison of superimposed data before and after matched filtering.
The instrument and its supporting processing technology can be used in the field of high-resolution seismic exploration of oil and gas, as well as shallow seismic exploration. Figures 5 and 6 show an application example in the desert area of Tazhong, China. Fig. 5 shows the seismic stack data before and after receiving and matching by the dedicated coupling geophone. The left figure shows the unmatched partial stack section, and the right figure shows the matched corresponding partial stack section. As can be seen from Figure 5, after special coupling matching, the interlayer information on the superimposed profile is increased and the resolution is improved. Fig. 6 shows the frequency spectrum of seismic stack data before and after being received and matched by a special coupling detector. Fig. 6 directly reflects that the frequency band of the reflected wave of the target layer is well broadened (the high frequency band can reach nearly 100Hz).
The special coupling geophone and matching processing software were jointly developed by Zhejiang University and Jilin University and provided by Zhejiang University. At present, the products are mainly used in desert areas, and have been tested and applied in Tarim desert area in China and Mu Us desert area in Erdos, belonging to mature equipment and software. Optimal coupling matching method for receiving seismic data by special coupling geophone, patent number: ZL2005 1004934 1.9, patent authorization date: August 20, 2008.