| It has been more than60years since vibrator was first used in the1950s in the former Soviet Union and the United States. At the end of the1950s, the former Soviet Union developed the first eccentric wheel vibrator, and then developed a hydraulic vibrator. A vibratory seismic exploration method on the basis of excitation encoding signal was thereby developed. However, it wasn’t until the end of1970s that the vibratory seismic exploration method really moved toward industrial production. In1952, Continental Oil Company (CONOCO) started the continuous vibration test. With a massive vibrating body striking against a vibratory plate tightly coupled with the earth, a group of elastic signals are imparted continuously into the ground. Information related to the underground geological structure, stratigraphic lithology, oil and gas bearing conditions in strata can thereby be obtained through processing the said elastic signals transformed by the earth. The device producing continuous vibration signals is generally called vibrator. The same as the former Soviet Union, since establishment of the first vibroseis crew in1956, it was not until1970s that the real production of vibratory seismic exploration began in America.Besides the features such as "Safety and environmental protection", vibratory seismic exploration can also adjust parameters such as the size of force, frequency range, sweep time, phase and so on according to specific near surface and deep geological conditions. It is because of the above-mentioned characteristics that vibrator holds an important position in the field of seismic exploration. Comparing the use of vibrators at home and abroad from2004to2008in CNPC, it is not difficult to find out that there is still a large gap in using vibrators at home and abroad. There are a total of531seismic survey projects at home, only44projects use vibrators, the ratio is only8.3%. There are a total of413projects abroad,234projects use vibrators, the ratio is56.5%. The survey areas of only6.8%of the44projects are more than500Km2. However survey areas of47.5%of the234foreign projects are more than500Km2. Most domestic vibrator-sourced projects are at Gobi, accounting for68.2%of the total projects, only4.4%of the total projects are at desert. However foreign vibrator-sourced projects are mainly at desert, accounting for40.3%of the total projects, only34%of the total projects are at Gobi. Aiming at the current status of the use of vibrator at home lagging behind, on the basis of large amount of investigations and researches on new technologies and new methods, combined with the scientific research project undertaken on duty, the author carried out related research to promote the domestic use of vibrator-the "Safety and environmental protection" seismic exploration method. Since dynamite source, the main seismic excitation source cannot accommodate itself to the needs of security situation, promotion of vibratory seismic exploration technology has great significance. First of all, it satisfies the needs of the national security, which includes two aspects such as safe production and social security. The second, it satisfies the need of environmental protection since its incomparable advantage in environmental protection. The promotion of vibratory seismic exploration faces a series of technical problems. The first is the productivity; the second is data fidelity. It can be seen from the current technological developments that both these two issues have been solved successfully abroad.On the basis of research, the author divides the development of vibratory technology into three stages:the first stage is from the beginning of1950s to the end of1960s, which is called the pilot stage. It is a stage focusing on the research and development of vibrator system, which is mainly developed and perfected through field acquisition test. The second stage is called large-scale application stage, which is from the beginning of1970s to the end of1980s. This stage is commonly known as the conventional production stage of vibrator, where source array of multiple vibrators is generally used to get the field single shot record through cross-correlation. It is a point-by-point shooting stage with very low field productivity. In the late of this stage, the field productivity is only300-500shots per day. The third stage is the high efficiency vibratory acquisition stage, which has been developed since the early of1990s up to now. Several techniques such as Flip-Flop Sweep, Slip-Sweep, Independent Simultaneous Sweeping (ISS) and High Fidelity Vibratory Seismic (HFVS) emerge successively on this stage. At present, the highest productivity of vibratory seismic exploration is up to20000shots per day. With the emergence of high efficiency vibratory seismic acquisition, it is becoming more and more urgent to deal with problems such as harmonic noise and adjacent noise. Also, with the appearance of HFVS of multiple vibrators, separation of high fidelity data requires in-depth study. Suppression of harmonic noise and adjacent noise and separation of high fidelity data all fall into preprocessing of raw data, so the author calls them "preprocessing techniques of vibratory seismic data". Some techniques use mature mathematical methods, since these mathematical methods were applied to vibratory seismic exploration only recently, they are still called "new preprocessing technique of vibratory seismic data". Focusing on high efficiency vibratory seismic acquisition and high fidelity acquisition, the thesis carried out theoretical and applied research concerning related new techniques of acquisition and processing.The thesis consists of five parts. The first part focuses on the development of vibratory seismic exploration, where development history and current status, fundamental structure and features of vibratory system and conventional field operation method of vibrator are introduced.The second part describes the theoretical basis of vibratory seismic acquisition. Here the dynamite-sourced and vibrator-sourced shot records are compared, linear sweeping signal of vibrator is introduced and features of other sweeping signals are evaluated. Focusing on the basic principle of compression method of vibratory record-the basic principle of the relevant law, the thesis also analyzes the features of secondary interference wave of vibrator-the harmonic noise. Meanwhile, the thesis also discusses the convolution model of reflection wave, brings forward the integral convolution model of vibratory seismic survey and illustrates the theoretical basis of preprocessing of vibratory seismic survey.The third part details a variety of field operation methods of high efficiency vibratory seismic acquisition and data processing methods of raw data. Here the conventional acquisition method of vibratory seismic survey is first introduced to illustrate clearly the high efficiency acquisition technique of vibratory seismic survey. Shooting at one shot point and then move to another shot point, productivity of the conventional vibratory acquisition is very low since there is only one vibrator fleet in the field. Here the raw shot records are acquired through cross-correlation of sweeping signal and vibratory records. The flip-flop sweep is the foundation of high efficiency acquisition. Under the premise of the same sweeping parameters, productivity of flip-flop sweep is1.5-2times the conventional vibratory acquisition. Flip-flop sweep uses two or more vibrator fleets in the field. When one vibrator group is working, the other vibrator group can move to next shot point and be ready for operation. When the working vibrator fleet completes the vibration and certain duration of record time, the next fleet starts to work. Slip-sweep technique is developed on the basis of flip-flop sweep. The difference between slip-sweep and flip-flop sweep is the slip-sweep allow sweeps to overlap in time. Slip time of slip-sweep should be equal or longer than the recording length. Due to overlapping sweeps of multiple vibrator groups, harmonic energy of one vibrator fleet will interfere with other vibrator group. This thesis illustrates in detail the features of harmonic noise in slip-sweep and the basic principles and application effects of its removal using filtering. With multiple vibrator groups working in the field and no need to wait for the currently working vibration to be completed to start sweeping the next vibrator group so long as it is ready, Independent Simultaneous Sweeping (ISS) is an acquisition method of high efficiency beyond imagination. In principle, we can shoot from the first shop point to the last shop point without intermittence in one working day so long as there is no hardware and software failure and natural interference such as wind, rain and so on. Unlike traditional methods, in ISS the recording system and vibrator fleets work independently and synchronized with GPS time, where the start time TO of each vibrator fleet should be recorded. However ISS will introduce adjacent noise to interfere with signal to noise ratio. Since adjacent noise shows the character of random noise on the common-receiver-gather, the method suppressing random noise can be used here to remove the adjacent noise. In this thesis we illustrate the3D-RNA noise removal method and its application effect in test work area. Other high efficiency vibratory acquisition techniques such as DSSS, HPVA, V1and DSS are also recommended in the third part. All these techniques are developed on the basis of slip-sweep and face the problem of harmonics suppression, which can be suppressed using the same noise suppression method. There is a very big difference in field organization between high efficiency acquisition and conventional seismic exploration. Related technologies including continuous recording systems, vibroseis control systems, high-precision positioning systems, real time massive data storage technology and so on are also introduced in the third part. Without these technologies, it is impossible to perform high efficiency acquisition.The fourth part, another section of consequence, highlights the HFVS. Both conventional seismic exploration and high efficiency vibratory seismic exploration acquire seismic records through cross-correlation of theoretical sweeping signal (real reference signal) and the recorded vibration. The process of cross-correlation between sweeping signal and vibration record is in fact the convolution between self-correlated zero-phase Klauder wavelet of sweeping signal and the pulse response of reflection coefficient. Each impulse response corresponds to a Klauder wavelet, thus compress a long vibration record into a short seismic record. It is notable that though there is some correspondence between the cross-correlated seismic records and wave impedance interface, the cross-correlated seismic record is only a mathematical response of the wave impedance interface, which can not reflect the real geological meaning of horizontal and vertical change of the wave impedance interface. The characteristic of this mathematical response is affected by the characteristic of sweeping signal. Research has been ongoing in the industry as to how to eliminate the influence of sweeping signal on seismic data. With the development of equipment, we can now record the acceleration signal of vibratory plate and hammer. These two acceleration signal can be used to calculate the best approximation signal imparted to the ground-the ground force signal, which can be used to design filters in the industry. It is the basis of HFVS that processing the vibration records using deconvolution to acquire the high fidelity seismic data free of influences of sweeping signal and ground force signal. In real operation, multiple vibrators are generally used to simultaneously collect high fidelity data, thereby introduced another problem-data separation of different vibrators. The thesis introduces the basic principle of the singular value decomposition (SVD), a method can be used to separate high-fidelity data of multiple vibrators, which has been confirmed by real experimental data. HFVS possesses the following five advantages:Can acquire high fidelity vibratory seismic data with the impacts of sweeping signal and related noise avoided; Comparing with related vibratory seismic data, vibratory seismic data obtained from HFVS show higher signal to noise ratio; Solved the intractable first breaks picking problem of vibratory seismic data, improved accuracy of first breaks picking as well as static corrections; Suppressed harmonic noise; Solved the vibrator-ground-coupling differences in one project.The last part of the thesis describes the trend or direction of vibratory seismic exploration. The author believes that large-tonnage vibroseis exploration, low frequency vibroseis exploration technology and the combination of high efficiency, high fidelity and low frequency are the future directions of vibroseis seismic exploration. The thesis details the current development status of above technologies, gives typical instances and finally comes to this conclusion. |
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