Research On Inversion Method Of Fracture Parameters In TTI Media

The fractures developed in the reservoir control the oil and gas distribution and seepage system in the reservoir.When fractures develop in the reservoir,the permeability will increase significantly.The improvement effect of fractures on the permeability of the reservoir is the key to the accumulation of many tight clastic rock reservoirs.When the long-wavelength assumption is satisfied,the non-uniform fracture-type rock with directional arrangement can be equivalent to a uniform anisotropic equivalent medium.Starting from the equivalent medium theory of fractured media,this paper mainly studies the inversion method of fracture parameters of TTI(Titled transversely isotropy)media,so as to realize the accurate estimation of fracture parameters of inclined fractured reservoirs.Provide accurate and reliable elastic and physical parameters for the exploration and development of fractured gas reservoirs.In this article,firstly,I derive the approximate formula of TTI media azimuth primary wave reflection coefficient,which characterizes the fracture weakness.Then,I discuss the relationship between the reflection coefficient in TTI media,fracture parameters,azimuth angle and other influencing factors.Secondly,I used AVO(Amplitude variation with offset)gradient attributes and amplitude ellipse fitting to calculate the fracture azimuth of TTI media.Thirdly,on the basis of AVAZ(Amplitude variation with incident and azimuthal angle)theory,I used the SCAM-MCMC algorithm to use the azimuthal seismic data difference to avoid the influence of the isotropic background part on the anisotropic disturbance part,and directly inverted fracture weakness and fracture dip angle.Finally,based on the difference in the azimuth seismic data,I used the damped least squares algorithm to invert the fracture weakness and extract the fracture dip angle.The two inversion methods are respectively applied to different fracture dip angle conditions.The AVAZ inversion method of azimuth difference based on SCAM-MCMC algorithm can accurately and reliably invert the reservoir fracture dip angle.This method does not need to limit the range of fracture dip angle and is suitable for reservoir development guidance with high quality seismic data.The azimuth difference AVAZ inversion method based on damped least squares algorithm,I adopt the discarding of higher orders to ensure the stability of the inversion.Thus,the reflection coefficient of TTI medium is linearized and the number of parameters to be inversed is reduced.Through the above measures,the uncertainty of the inversion of unknown fracture parameters are effectively reduced,and a reasonable and reliable method is provided for the prediction of fracture parameters.However,limited by the assumption of high fracture dip angle or low fracture dip angle,this method is suitable for the exploration and development of fractured reservoirs whose fracture dip angle range meets the assumed conditions.