The Study On Near Surface Structure Surveying By Surface Wave And High-Resolution Processing With Well Data

As the development of the petroleum exploration, seismic exploration has been developed from the simplex studying of structure to the studying of complex structure and the detecting of the lithology. All of these new researches depend on the improvement of resolution of the seismic exploration and the ratio of signal-to-noise. If the resolution and the ratio of signal-to-noise are not good enough, the technique of seismic exploration is too hard to get improvement on the study of reservoir and describing of the petroleum reservoir.The improvement of the seismic resolution is a systemic project including three important steps which are date collection, processing and interpretation. The technique of wield date collection and constructing quality have been developed greatly in these years and can not get more improvement for the limitation of the seismic theory and wield equipments. In these years there are several new techniques such as coherence cube, frequency diversion, attribute's fusion and so on appearing in the seismic date interpretation techniques. These new techniques could find out the weak signal about sand bodies in the seismic date. But there is still a question which is if there is still some useful information about sand bodies has been kept in the seismic date? So the most important point stays in the second step-the processing of the seismic date. Based on the foreland of the subject and the fact of oil exploration, and aiming at improving the seismic date resolution, the dissertation is extended roughly by three aspects: the feasibility of using of MASW on the accurate study of near surface structure, the use of well data (including up-/down-hold data and VSP data) and the corresponding software's development and the study on the attenuation characters of the linear transitional medium.1. The refraction and the up-/down hold methods are the ordinary ways in the research on the near surface structure of the desert area. The former has some limitations in the theories and precision, and the latter, on the other hand, mostly could be used for the controlling point of the structure for its high cost and construction difficulties. So it is necessary to find out a new technique which has the character of low cost, high precision and easy to operate. The surface wave method could be used in the petroleum seismic exploration for it has been successfully used in the engineering works and there is surface-wave information in the ordinary seismic exploration record of the desert area.On the area of the petroleum seismic exploration, surface wave should always be eliminated as noise. But materially, as the same as body waves, it has various useful information on the underground medium. As we known, surface wave exploration uses its frequency dispersion character in the heterogeneous medium which is that in the heterogeneous medium the phase velocity of the surface wave is the function of the frequency, it changes as the frequency changing. At the same time different depth has different frequency, so we could get the elastic information of the medium on different depth. In this paper, we firstly prove theory that the possibility of using MASW method for research on the structure of near surface medium in desert medium by making different models with different elastic parameters as character of the desert area, forward modeling the small layout MASW record by calculating the 2-D heterogeneous elastic wave equation using the finite difference method, and analyzing the forward and inversion result. The successful using of MASW on studying the structure of near surface medium in Neimenggu Maowusu desert and Xinjiang Takelamagan desert provided the practice proof for its feasibility. Specially, in the later one, we firstly used two different datasets to describing the near surface structure, i.e., the designed multi-channel record and the extracted multi-trace record from the ordinary seismic exploration record. By analyzing the two records with MASW, it is constructing the accurate structure information about 60m underground surface on some survey line in Talimu. This information does not only tally well with the up-/down-holes result but also become more various in details. The subsequent experiment on static correction makes a good direction for the processing of the surface wave date. Both of the theory discussion and practicing result prove that it is feasible to use the surface wave technique on studying the near surface structure in the desert area. In this paper, we make a new way on near surface research which could be use in production and has good future.2. In the year 2005, Tian Gang put out the theory that using the up-down hole method to compensate the near surface medium's attenuation on the seismic signal. This theory gets outstanding result on its practice. But the traditional date, collected by up-hole method, i.e., shoot in the well and collected in the ground, is hard to be used in processing of compensating processing. The ordinary way to dealing with the problem is to carrying out the special designed field layout to get the useful date used for compensation processing, but this way inspires the questions on cost and efficiency. In the paper, we put out the common shot gather method to deal with this question which gets rid of the source problem and make it possible for the using of traditional up-hole data to compensation processing. Other date collecting methods such as down-hole data also could be used in processing of compensating inversing filter under some conditions. This will extend the using of the the up-/down-hole method for compensating seismic wave's attenuation and also provide a new way for the use of the traditional up-/down-hold date. In the paper we firstly study the theory compensating result and prove that there is a limitation of compensation in using the up-/down-hole method to compensating the near surface medium's affects. It is the fact that the compensating result is influenced strongly by the quality of the date itself. We also firstly put out the up-/down-hole compensation method in pre-stack date.It is proved that the up-/down-hole compensation method could be used to compensate the seismic signal attenuation, to improve the quality of high frequency component, and extend the frequency bandwidth on both of the pre-stack and post-stacked data.3. Processing the surface seismic date for extending the frequency bandwidth based on the VSP data could not only protect the low frequency signal, but also improve the high frequency signal to extend the frequency bandwidth and improve the seismic date resolution. The ordinary way to get the VSP record is to shot on the ground and collecting in the well. The seismic wave only gets across the near surface low-depressing layer once so it has higher resolution.The information of absorbing and attenuation in the propagating area is included by the VSP down-going wave. From the point of system, if the inverse filters of the propagating field are computed, the attenuating relative high-frequent component of frequency and amplitudes of seismic signal could be recovered. Due to the regular VSP down-going wave is based on the given time interval to complete the compensating processing of inverse filtering, a series of problems would appear during the regular compensating process in some area where the subsurface medium changes fiercely. For those problems, the author has brought out a new method, which is dependent on slid time-variant compensation inverse filter. The series of problems could be perfectly solved by the new way. Found in the application study of L3 line of some area in Daqing oil field, the stacked profiles, filtered by the VSP down-going wave compensating inverse filter, have protected the low-frequent components, as well as widening the high-frequent part by approximate 10 Hz. the goal of improving the seismic data resolution was realized by the new method, which supplies perfect application effects.It is a new way which uses the up-going wave filed corridor stacked data to improve the resolution of the surface seismic data. It is called the slid time-variant matching filter method. Base on the essential relationship between the VSP data and the near well surface seismic data, matching filter factors are firstly calculated and then are applied to the surface poststacked seismic data using the slid time-variant method. The same data were processed with this new method proposed by author; it is proved that the frequency bandwidth extend greatly, about 30Hz, without depressing the lower frequency components. Compare with the other VSP corridor stacked data through the test line L3, the signal that is weakened or depressed in the original seismic data is improved, and can match with the corridor data very well. Still, compare with the down-going VSP method, the method is a most effective and useful method, which reduce the dependence of the time-depth data.4. Base on the academic research and practice and aiming at using the well (up-/down-hole, VSP) data for extending the frequency bandwidth and improving the seismic resolution, the software is developed. Using this system the speed of the conversion from academic study to field work has been accelerated greatly. In the practice, this system has many excellences such as easy to operate stability and so on.5. By analyzing the up-/down-going record, there is heterogeneous medium which has transitional character and could be supposed linear transition. By analyzing the result of the 1-D and 2-D forward modeling, the linear transitional model is equal to high-pass filter to the transmission wave. As the linear transitional model become thicker, the attenuation of the low frequency becomes stronger. The model's transmission parameter swing change between 0.92~1 which indicates that means the low frequency of transmission is limited. So this so called high-pass is nearly equal to whole pass. On the other hand, the linear transitional model is equal to a low-pass filter to reflection wave. As the linear transitional model become thicker, the bandwidth of low-pass becomes narrower. In the paper, the parameter of the reflection model changes between 0~1 which indicate that the high frequency of the reflection wave changes from absence to entity.To sum up, the linear transitional model has different influence on the transmission of the seismic reflection wave from swing to phase, even to frequency. And all of these influences are stronger than the reflection wave transmitting in the even medium. The attenuation of reflection wave swing and frequency in the linear transitional model is coursed by the heterogeneous character. And this is decided by the medium's character and is also a description for the medium which is useful for study the lithology of the medium and could be helpful on the study of the seismic attenuation. For the transmission wave, the linear transitional model is equal to a whole transmitted filter and has little influence.