The Fluid Substitution Based On Gassmann Equation

With the oil and gas exploration and the deepening of increasingly complex oil and gas reservoirs, thus the focus from exploration of the structural reservoir to the lithologic reservoir, cover transfer of oil and gas reservoir type. Present-day seismic exploration technology to discover new oil and gas has become an important means of resources, rock physics technology has become the underground through the rock and fluid understanding of sound waves in response to the most effective way, while the seismic rock physics technology effectively and seismic rock physics research combine closely quantitatively describe the rocks and the relationship between oil and gas. Seismic data analysis is one of the key technologies for characterizing subtle reservoirs and monitoring subsurface pore fluids. Fundamental rock physics can help us understand seismic response of rocks and fluid properties. Fluid substitution is an important part of rock physics and is a tool of identifying fluid and quantifying formation, and it also plays an important role in AVO analysis.Propagation theory of seismic waves in fluid medium has been introduced in the paper firstly. In"Effective-Medium Model"section, the stress was analyzed the assumption and limitations for volume average model, self-consistent model, and scattering theoretic model, expound the self-consistent approximations to two-phase media, heterogeneous media, the geometry description to different shape inclusion, and the mathematic expression to a cracked media. In"Mechanism of Acoustic Propagation in a Fluid Saturated Porous Media"section, the kernel substance of seismic rock physics, emphatically expound Gassmann's relations, Biot's theory and BISQ (Biot-squirt) model, and what based on fluid flow mechanism. Comparative analysis attenuation and dispersion mechanism expressed in distinct model. In"Analyzing for Velocity Effects", many empirical relations was expounded in seismic wave velocity effected from rock density, porosity, clay content, saturation and correlated common empirical relation models, along with V P- V S relations and rock anisotropy research in laboratory. The significant technique in seismic rock physics analysis-fluid substation. Gassmann equation is an important theoretical tool for researching on rocks elasticity. Deduce the detailed calculation process of fluid substitution by use of Gassmann equation in the paper, and come to the equivalent value of the speed and density. Finally give out the density and velocity model diagram, and replace respectively a two-layer limestone when the porosity of 5% of the cases. At the same time, analysis and comparison of the replacement gas/water content of different porosity in the replacement of the replacement layer after reflection amplitude changes in different situations. At this point the smaller the porosity, the amplitude of the more intense the effect replaced the better.Reservoir in the actual applications, this article on the study area only when the purpose of drilling wells ma2 layer, and the once-ma2 drilling poor reservoir properties, there is no good for oil and gas show. Therefore, the carrying out of the wells ma2 study fluid replacement helps to extrapolate good reservoir properties have been in response to the characteristics of the earthquake. In accordance with the calculated velocity model for fluid replacement forward modeling, analysis of the different porosity(5%,8%,10%) of the reservoir at the time of the seismic reflection characteristics. Finally, with the actual information to draw the greater the porosity, Gassmann equation calculated using the equivalent speed of the lower, with the surrounding rock (limestone) of the material the greater the difference, after the layer of fluid to replace the reflection amplitude also will be stronger. In the end the actual information to draw with the increasing porosity of the reservoir to lower wave impedance and the surrounding poor increased, after the layer of fluid to replace the reflection amplitude will also gradually. This is in line with the actual situation, in order to provide a basis for fluid identification.