Studying On The Response Of Seismic Waves In Medium With Multiple Sets Of Multi-scale Fractures

Seismic wave anisotropy exists generally in the earth media. Anisotropyinduced by cracks is one of the important causes of seismic anisotropy. With theimprovement of degree of the exploration and development of oil and gas reservoirs,fractured oil and gas reservoirs become a very important target in the oil and gasexploration and development in China in that fractures are the main reservoir spacesand seepage channel for oil and the actual undergroud fracture distribution forms avery complex multiple sets of mult-scale fractured systerm. Fracture prediction isalso considered as an acknowledged difficulty. Therefore, it is of great significanceto study seismic wave propagation in the crack anisotropy medium.Studying the underground medium depends on the assumption of the mediummodels. So far, in oil and gas exploration and development, people have studied thefractured medium on the premise that there exists a single scale fracture set alignedin a vertical or horizontal direction. However, crack orientation has more than onepriority direction and the scale of cracks are distributed from a few microns to a fewmeters due to the affect of tectonic stress field. Therofore, in order to accurally getthe response characteristics of seismic waves in the anisotropy medium and satisfythe needs of production, the multiple sets of mult-scale characteristics of fracturesmust be taken into consideration and we must establish a fractured medium modelcloser to the underground actural reservior.In this thesis, on the theoretical basis of elastic waves in anisotropy medium,research and comparative analysis are carried on four kinds of effective mediumtheories-Hudson perturbation theory, Thomsen equant pore theory, Schoenberglinear slid theory and Chapman new theory; with finite element numericalsimulation method, we establish fractured medium models to study the relationshipbetween the characteristic parameters of fractured system and the characteristicattributes of seismic wave response. The results show that the propagation law ofseismic wave in multiple sets of mult-scale fractured medium is different from thatin isotropic medium, which shows significant anisotropy. Fractures have significanteffect on the response characteristic of seismic wave which changes with fractureparameters. We can get a more thorough understanding of the response characteristicof seismic wave in the multiple sets of mult-scale fractured medium in this studywhich provides theoretical basis for the detection and accurate description of thecomplex fractured system.