Wavefield simulation of fractured porous media and propagation characteristics analysis

Most fractured reservoirs are two-phase media, that is, mixture of solid matrix and void. It contains rock skeleton and fractures or pores filled with oil, gas and water. These fractures are the channels of oil and gas storage and migration. In two-phase media, the interaction between the fluid and solid phases will further complicate the seismic wave propagation. Natural fractures are typically irregular in shape, thereby causing difficulties in the exploration of fractured reservoirs. Therefore, the key to the prediction of fractures is to study the equation of motion of seismic waves and energy distribution of seismic waves at the fracture interface. To derive the propagation law for complex irregular shape fractures in two-phase media, we combined the stiffness matrix of the media with linear slip theory and derived a numerical simulation scheme. The simulation scheme considers the fractures in the two-phase media to be in any direction. In addition, seismic wave energy distribution at the fracture interface was obtained. The linear slip boundary condition was introduced into the conventional Zoeppritz equation, and a modified Zoeppritz equation was proposed for two-phase fractured media. The reflection and transmission due to the fracture interface were considered in the new equation, thereby making the equation more flexible. Using the new numerical simulation scheme, we analysed the elastic waves produced by the linear slip fracture interface in two-phase media and provided the long-term stability results of the new scheme. Moreover, we provided the relationship between the reflection and transmission coefficients of the linear slip fracture interface and the incident angle and compliance in two-phase media using the new Zoeppritz equation. The results show that the reflection wave of two-phase fractured media can be divided into wave impedance and fracture parts to accurately describe the properties of underground rocks.