Seismic Rock Physics Modeling And Its Application In Oil Shale Exploration

Seismic rock physics is the subject to study the relationship between rock physical properties and seismic responses. It focuses on the effects of rock physical properties such as lithology, porosity, pore type, fluid type, fluid saturation, frequency, etc. on rock elastic properties with the aim of establishing the relation between the reservoir physical parameters and seismic characters. Rock physics can bridge seismic data and reservoir properties. It includes two parts, one is rock physics modeling, and the other is rock physics analysis. Rock physics modeling is to offer an effective medium model for simulating the elastic moduli of actual rocks. The success of rock physics analysis is dependent on the accuracy of rock physics models. Therefore, the rock physics modeling is the foundation of rock physics research, but also the most important part.Through studying the theories of seismic rock physics modeling, the paper summarizes the methods of the seismic rock physics modeling, and establishes the process of base on modeling rock matrix, rock frame, fluid saturated rock and pore fluid basing on the Gassmann equation. By forward modeling, velocity prediction and Biot coefficient calculation the paper finds the problems in the process of rock physics modeling, especially in the modeling of rock frame, and points out that the Kreif model and the critical porosity model does not apply to low-pressure or low-porosity rock.For the defect of traditional critical porosity model, the paper develops and amends it on the basis of its basic principle, points that the critical porosity is variable and is a function of pore shape, and establishes a new model called variable critical porosity model. Also the paper proposes a new method of calculating the critical porosity, and introduces the new variable critical porosity model into S-wave velocity prediction, which improves the accuracy of the prediction greatly. Oil shale is a sedimentary rock which riches in organic matter, and can burn and produce shale oil which could be used as an alternative energy of natural oil and gas, so the oil shale is an important potential resource. At present the identification and evaluation of oil shale is mainly relying on logging method, while the research about seismic and seismic rock physics is very weak. On the basis ofâ–³logR method, the paper proposes a new method of overlapping acoustic impedance and conventional logging response characteristics of oil shale. With the establishment of oil shale rock physics model, the relationship between organic matter content and the velocity can be determined. And on the basis of the oil shale rock physics model this paper proposes a new method to calculate the organic matter content by the inversion of velocity.