Summary
Seismic reservoir fluid identification is the main goal of current pre-stack seismic inversion. Effective fluid bulk modulus is an effective fluid factor which can provide persuasive evidence for fluid identification. Under the theory of poro-elasticity, we deduced a PS wave linear AVO approximation equation based on effective fluid bulk modulus, dry rock matrix term, porosity and density. And we tested the accuracy of new derived equation by using a typical model. According to theory of joint PP-PS wave inversion, we tested the method on seismology of a real logging well data by comparing with single PP wave inversion. The result showed that the estimated parameters can agree with original data more accurately. Meanwhile, a real multi-component seismic data was used to verifying effectiveness and feasibility of new proposed algorithm. It showed exact effective fluid bulk modulus, dry rock matrix term, porosity and density estimated value can be obtained directly, which can avoid the error accumulation of indirect inversion. It can meet the demand of seismic fluid discrimination.
Introduction
Joint PP and PS wave AVO inversion as an effective seismic inversion can enhance the accuracy of seismic inversion because of adding constraint of converted wave. It is based on Zoeppritz equation which can be simplified by linearization techniques. PP and PS waves can be expressed by different elastic parameters (Aki and Richards, 1980; Jeffrey L, 1999). In order to enhance reservoir prediction and reduce seismic inversion ambiguity, threeterm joint PP and PS seismic inversion was executed by SVD algorithm, and it can get better inversion result than two-term inversion (Faranak, 2004; Helene, 2006).
Fluid identification is one of main objects of reservoir geophysics. Russell(2003, 2011) presented fluid factor r f and f which are concerned with fluid information and a new reflection coefficient equation is derived under the instruction of Biot-Gassmman theory. Yin(2014) proposed a new PP wave AVO approximate equation based on matrix-fluid decoupled, which can highlight respond of fluid item. Then, in the framework of Byes theorem, they developed pre-stack seismic inversion which can obtain effective fluid bulk modulus, rigidity, porosity and density.
