The Seismic Response Study Of Multiphase Fluid Patchy Saturations Rock Temperature-dependent

With the deepening of oil and gas exploration and development, the goal of oil and gas geophysics exploration become more complex, having transferred from the universal structural reservoir to lithology reservoirs and subtle reservoirs. On the one hand, the exploration targets gradually become deeper smaller, more difficult exploration, the prediction accuracy requirements are also increasing. On the other hand, the key goal of reservoir prediction in addition to determine the existence of the reservoir, forecast level of reservoir development is good or bad, also need to determine the quantitative nature of the fluid contained in reservoir, fluid reservoir characteristics of the wave field. The quantitative determination mainly rely on seismic rock physics to set up the "bridge" between the relationship of seismic data(properties parameter) and oil reservoir characteristics(elastic parameters). Seismic rock Physics main use the intrinsic relations of reservoir rock and its pore fluid versus the seismic property parameter. Based on the systematic theory and media models of rock physics property such as elastic, viscoelasticity and anisotropy in rocks, the empirical relations between seismic attribute versus reservoir property parameter are established. Using the techniques such as fluid substitution and so on, provides the reference fundamentals for lithology reservoirs and subtle reservoir exploration. The core of fluid substitution is the Gassmann effective medium theory, Based on this, using Gassmann equation to numerically simulate elastic parameters is meaningful. After determining the Gassmann effective medium theory is the core content, I introduce some important theoretical models of petro physics, such as the assumptions and application conditions of HashinShtrikman bounds, V-R-H average model, Wood fluid modulus formula, Kuster-Toks?z theory and the fluid mechanism model of porous media(Gassmann equation, Biot theory and BISQ model). And some of the classic speed equivalent empirical formulas are summarized.Since the capillary pressure, each lithology has different fluid pressure, so that the fluid saturation is different. When the capillary pressure keep equilibrium,according to three phase saturation fluid Brooks-Corey model, Gassmann theory and bound theory, we build the quantitative relationship between inhomogeneous saturated rock acoustic properties and water saturation. We calculate the seismic response of inhomogeneous saturated porous rocks and reveal the variation between seismic velocity and water saturation in different saturated fluid.If we want to predict the reservoir properties from measured seismic velocity, it is essential to verify the rock physics model. Because certain factors such as pore space deformation, fracture density, fluid saturation, tectonic stress, lithology and temperature et al. may probably lead to the deformation of seismic velocity space. It is very important to describe the influence of temperature on seismic wave velocity attenuation by analyzing and simulating the key attributes of rock sample saturated with hydrocarbon. According to different temperature environment, this paper modifies Gassmann’s equation to reaction temperature. As to different lithology, this paper verifies consistency of modified Gassmann’s equation when there is fluid substitution and actual measurements. Also, we calculates the change of the Q value. For the seismic response at different temperatures, one explanation is that Gassmann equation assumed that shear modulus is not affected by the presence of fluid, due to the weakness of chemical machinery caused by fluid. The shear modulus of the pore fluid saturated rock has a significant impact, especially when micro cracks appear under high pressure and high temperature. Another explanation is that physical properties of the fluid change when the temperature is not the same, including density, viscosity, speed and modulus and so on, which leading to the differences of seismic response of the fluids saturated rock.Based on the velocity of rock saturated with water varied with temperature, this paper discusses temperature-dependent fluid substitution by Gassmann of multiphase inhomogeneous saturated rocks. It shows the difference between seismic velocity of rocks saturated with different fluid, providing reliable rock physics basis for identification of oil and gas reservoirs.