A Study On Seismic Response Characteristic And Identification Technology Of Fluvial Sandstone Reservoir

In recent years, along with the deepening of the oil-gas exploration development, some collected strap of oil and gas has been found in the river way enclosed by sandstone lithology in many basins of our country and industrial oil has been obtained. The combination of mid-top oiliness in Chang-heng area of Da qing city has been put into operation for 40 years with the steady production of 5000×10~4t. There have abundant oil resources as it is located among the sunken area of Qi jia-Gu long and San-zhao. The Fuyang oil reservoir stratum of these area is mainly composed by delta diffluence plain river way sandstone and delta former underwater diffluence plain river way sandstone, and these river ways interlace each other with reticulation and make sand body overlapped and connected in planes so that a good reservoir formation space will be provided for a large area of lithological oil and gas.The sandstone of Fuyang oil reservoir overlaps and connects with each other because it transfers and swings frequently in the time of sediment, and the monolayer of these sandstone is so thin at 1～5 m, therefore identifying the river way and finding the thicker river way sandstone is the key of exploration for Fuyang oil reservoir and a difficult problem as well. This paper has been done in resolving the following problems:(1) A geology model has been established that describes reservoir sediment and distribution on the base of characteristics of reservoir geology in the research area. Through the modeling technology and on the assumption that the condition of underground geology is known, the fundamental of seismic kinematics and kinetic are used to calculate the response from the geology model which has been given.The geology models constructed in this paper include: fluvial folded sandstone model,sediment sandstone model in different time and sand model with different sediment character. Through the analysis of these models we can see that the sand stone in different periods has different imaging character for its different distributional manner. So we can conclude that the major factor influencing seismic imaging is configuration of sandstone overlapping and sandstone velocity. At the same time, we use the method of two steps finite difference to resolve sound wave equation to model the seismic geology on the base of actual seismic date that has been interpreted. We select the adopted modeling parameters and observation system parameters to obtain seismic response, using post stack time excursion and pre-stack deep excursion to revise the location. To compare the answer with actual seimic date so that the actual date is true or false can be judged and estimated.(2) The sandstone thin bed layer presents transverse isotropy for the difference between low velocity wave spread vertically upon the layer and high velocity along the layer. However, the axis of medium will not be vertical when the lay rots for draping and up rushing. So the layer is not horizontal but strikes upward. In this case, the difference will be more obvious for the difference of velocity of vertical and horizontal layer because of anisotropy. In the slope anisotropy, the numerical value of velocity changing with radial angle will affect profoundly the travel time from reflecting layer underground, i.e. apparent velocity abnormity.To analyze the influence of sandstone reservoir imaging that anisotropy makes, we use innerving girding finite difference to model anisotropy imaging of sandstone. We can see that the reflected elastic wave in TTI media include qP wave,qSH wave,qPSV wave,qPSH wave, the transmit wave include P wave,SH wave,SV wave and divert wave; axis of wave front deflexed, the mini travel time of qP wave excursed, this will cause disturbance of geology construction in actual seismic imaging. Simultaneously, we analyze the influence of Thomsen anisotropy parameters to seismic wave travel, and the influence is obvious when anisotropy parameter to elastic wave aversion distance changes, especially when the angle of incidence of reflected wave is bigger than critical angle in the far distance. So the fortification of the phase appears in the far distance on the seismic section. Further more, the influence that Thomsen parameters on vertical and horizontal wave are not the same, the influence on vertical wave is weaker than horizontal wave.(3) In recent years, high differentiate seismic explorations of 2D and 3D have been done in Chang-yuan, the technology of 3D seismic exploration complex ground surface condition is mature, which offers a information base to take a fine forecast and study of reservoir of Fuyang oil layers. On the base of these, we take the technology of compensate radiation and absorption of sphere in the field of time,frequency and space to improve the resolution. Utilizing these technologies, we have eliminated the effect of excitation in the near ground surface,frequency difference and false reflection and improve the resolution of datum. Using the method of restrict reversion, and basing on the geology model, we take the way of synthetic seismic record and wave impedance reverse to demarcate thin layer and the arithmetic model pre-select iterative disturbing. By modifying and updating the model continuously, we have successfully made the synthetic seismic modeled record ideally match real earthquake data.Applying the technology of spectrum decompose which is based on generalized S transform, we construct normal wavelet with parameters of swing,rate of energy attenuation,time of energy postpone and apparent frequency, the disadvantage of changeless normal wavelet in S transform has been overcome and we have attained a finer imaging effect than spectrum decompose based on Fourier transform, so a forecast in terms of quantity and quality for Fuyang research oil layers can be realized.