AVO Analysis And Fluid Identification

As the development of the seismic exploration for petroleum and gas, it is harder to identify the fluid by using only one or little information. So people wish to get more information which can reflect stratum fluid from the seismic data.In the recent years, lots of scholars have done some researches about fluid identification based on P-wave and S-wave. The researches show that the S-wave information is more effective to reflect fluid than P-wave information. But because of some reasons, such as the cost and difficulty to achieve and utilize the S-wave exploration and so on, it has not been applied widely and developed well. At the same time, it also suggests that if the incidence angle of seismic wave equals zero, there will be plane wave in the interface. Otherwise, there will be P-SV wave. In other words, different angle gathers reflect different fluid informationg, different fluid information reflect different seismic information. So it supplies one effective method and direction for identification fluid that utilizing the P-wave, S-wave and P-SV wave comprehensively. Based on those, the relational technologies of researching amplitude variation versus offset which are represented by AVO, have been studied deeply today. Moreover, AVO technology is based on rock physics and system, strict mathematical calculation, besides that, it can also reduce noise in some special process. And by AVO analysis, we can get some S-wave information from P-wave seismic data.We know that if the incidence angle of seismic wave equals zero, there will be plane wave in the interface. Otherwise, there will be P-SV wave. So the near-angle reflection wave contains more P-wave information and far-angle reflection wave contains more S-wave and fluid information.That is also the foundation of the wide-angle reflection research. In the attributes of different angle stack gathers, there is an apparent difference in the place existing fluid, but there is no apparent difference in the place without fluid.For those, the AVO technology is developed rapidly and utilized widely and become a very important method for reservoir prediction and oil and gas exploration. Firstly,this paper introduces the fundamental principles and rock physical foundation by learning the background, development history, present status and development trend of AVO. And talks about the researching purpose and meaning.And then, introduces the basic theory of AVO, includes the rockphysic foundationg and geophysical foundation, also introdeces the Zoeppritz equation and its different approximate equations,and discuss the accuracy of different approximate equations. And combined with parameter model, analyzes the AVO response characteristics of four categories of gas sandstone, at the same time, also analyzes the the AVO response characteristics carbonate stone, researches the AVO attribute parameters and lithologic parameters inversed from the pre-stack informations,further reveals the variable feature of lithology and pore fluid.And then, this paper introduces one new fluid identification factor idea and fluid identification factor based on angle gathers by researching the pre-stack seismic data. It also introduces another high sensitive fluid identification factor based on post-stack seismic data by using the union inversion of P-wave impedance and S-wave impedance in AVO analysis. In this paper, there is an analysis about the sensibility of different fluid identification factors. By the numerical experiment and practical application, the results show that the fluid identifying factors in this paper are more effective comparing with other factors.