Research On Fluid Detection Method Based On Seismic Frequency-dependent Attributes

Oil and gas exploration and development show that fractured reservoirs are a very important type of oil and gas reservoirs in China's petroliferous basins,and fluid detection is an effective means to improve efficiency.At present,most models discuss partial saturation and aligned fractures separately,and then usually both attenuation phenomena exist simultaneously in the fractured reservoir.In this paper,the Ordovician carbonate reservoirs in the Tarim Basin are research object,and the effects of fluids on seismic response characteristics are studied by constructing a reasonable petrophysical model.This paper focuses on the construction of the fractured porous medium model,and the fluid detection method combining the frequency-dependent AVO inversion method with the petrophysical model,and applied it to the Shunnan area of the Tarim Basin.Firstly,the paper constructs a fractured porous medium model containing both aligned fracture and partial saturation effect,which combines periodic lamellar porous media with Chapman theoretical model.We calculate the P wave elastic modulus of the two-phase fluid porous medium model when the P wave is perpendicularly incident.Then,based on the elastic parameter upscaling theory,the stiffness matrix of the periodic layered porous medium can be obtained from the stiffness matrix of the high and low frequency limit states and the elastic modulus at the normal incidence.Finally,the Chapman model is used to introduce the crack correction term into the periodic layered model to simulate the squirt flow effect of the fracture.Based on the model,the dispersion and attenuation characteristics of the P and SV waves of the fractured porous medium are numerically simulated.The results show that the P wave dispersion decreases with the increase of the incident angle,and the SV wave dispersion increases first and then decreases with the incident angle.The attenuation of fractured porous media is the result of a combination of partially saturated and aligned fractures.The numerical simulation results show that as the saturation of the gas increases,the partial saturation effect decreases and the effect of aligned fractures increases.Theoretical studies on dispersive media have shown that the frequency attenuation gradient property is an important method for reservoir prediction.With the development of time-frequency analysis methods,the understanding of seismic data is extended from the time dimension to the time-frequency dimension.Four time-frequency analysis methods are compared and analyzed.The results show that the generalized S-transform can be better applied in actual seismic data.The "low-frequency shadow" technique shows a trend of energy enhancement in the low frequency,while the frequency attenuation gradient focuses on the energy attenuation at high frequencies.At the same time,using the "low-frequency shadow" technique and the frequency attenuation gradient for reservoir comprehensive prediction can improve the prediction accuracy.Further,this paper combines a multi-scale fractured rock physical model and frequency-dependent AVO inversion method to establish a set of fluid detection technology.Firstly,based on the drilling,logging,seismic,and geology data,we use the Chapman equivalent model to simulate the fractured reservoirs in Shunnan area,and use the reflectivity method for forward modeling the seismic wave response feature of reservoirs saturated with different types of fluids.Secondly,it is necessary to carry out the seismic attribute sensitivity analysis of different type reservoirs to determine the seismic dispersion is more sensitive to fluid.Finally,based on the situation of seismic data in the study area,we establish a technical process based on the petrophysical model and the frequency-dependent AVO inversion,and apply it in Shunnan area.The results of fluid detection and real drilling verification show that the method proposed in this paper has a good practicality,which provides a method for the fluid detection of this type of oil and gas reservoirIn addition,the fluid saturation prediction method of the fractured porous medium model is also studied.Based on the fracture development characteristics of Yijianfang formation in the S area of the Tarim Basin,the modeling method of fractured porous media model is improved.Based on the improved model,the dispersion and attenuation characteristics of the fracture reservoir are analyzed.The results show that the P wave attenuation increases with the increasing of water saturation in the seismic frequency range.Then,the Zoeppritz equations for the frequency-dependent reflection coefficient and transmission coefficient at the interface of the isotropic layer and the vertical symmetric isotropic(VTI)layer are re-derived.The analysis of the five well model data and the actual data frequency-dependent AVO inversion in the study area indicate that the P wave dispersion is mainly affected by water saturation and permeability,and the reservoir water saturation directly affects the dispersion intensity,while the permeability influence the attenuated frequency band range indirectly affects the P wave dispersion intensity.