Study On Method And Application Of Geostress Prediction With Seismic Data

In recent years,due to the increasing consumption of conventional oil and gas resources,the exploration and development of unconventional resources such as shale gas etc.has gradually become the research hotspot.The shale gas reservoir is characterized by low porosity and low permeability,and the hydraulic fracturing transformation should be performed during mining to make sure that,a lot of fractures are formed in the shale.The ground stress is the critical factor that determines the shape,orientation and extension direction of the formed fractures.Reliable estimation of ground stress of shale reservoir helps choose the areas susceptible to the net-fracturing,improve the recovery efficiency and yield of shale reservoir,so it is one of necessary step of exploration and development of shale reservoir.In the paper,starting from the fundamental theory of ground stress and the fundamental theory of seismic anisotropy,we introduce the basic concept,composition,distribution,influencing factors of ground stress and the contribution that the ground stress made to the oil-gas exploration.We present the constitutive equations of elastic medium,and display the stiffness tensor that characterizes the elastic property of anisotropic medium.Then,we generalize the anisotropy parameters of different media and the conversion relationship between them,and sort out the relationship between the elastic stiffness constant of different anisotropic medium and the anisotropy parameters.Meanwhile,we discuss the relationship between the fracture rock physical parameters and the anisotropy parameters,laying a theoretical foundation for the ground stress formula deriving.Starting from the constitutive equation of anisotropic medium,based on the fundamental theories of seismic anisotropy,we determine the stress indicators of fractured reservoir and establish the quantitative relationship of the ground stress to the elastic parameters and the anisotropy parameters,and derive the accurate formula for the ground stress of HTI medium and OA medium and the differential horizontal stress ratio.Meanwhile,the differential horizontal stress ratio of OA medium is defined as ODHSR(Orthorhombic Differential Horizontal Stress Ratio).Meanwhile,the linear slip theory is adopted to simply to the accurate formula of OA medium and the relationship between different calculation formula for inter-media ground stress is studied.Then,we introduce the basic elastic parameters,and provide the establishment process of seismic rock-physics model of unconventional reservoir,and analyze the influence of reservoir physical property parameter on DHSR(Differential Horizontal Stress Ratio).Finally,according to the logging curves estimated by the rock-physics model,the formula verification and model test are adopted to verify the formula derived in the paper and prove the rationality of formula.Based on the quantitative characterization of seismic rock physics parameters of ground stress of shale reservoir,we introduce the establishment of exact equation and approximate equation of azimuthal reflection coefficient,and provide the elastic impedance equation of azimuthal anisotropy,and explore the inversion method of anisotropy parameter based on the seismic data of pre-stack azimuth.We study the seismic prediction method by estimating the ground stress with azimuthal seismic data.Meanwhile,according to the approximate formula of ground stress for the orthotropic media,the influence of elastic parameters and anisotropy parameters on the estimated ODHSR are discussed to evaluate the credibility and stability of ODHSR.In the paper,the ground stress inversion method based on orthotropic media is adopted to perform application researches on the actual work area of one shale reservoir named A work area.The application results show that,ODHSR inverse result is matched with the azimuthal seismic data by adopting ground stress inversion method based on the theory of orthorhombic anisotropic medium,and it has good resolution and lateral continuity.The inverse result can indicate areas where the rock will have a greater tendency to fracture into a network and it is identical with the drilling results and applicable to the practical geological conditions.It brings relatively good application results and proves the feasibility and validity of such method.