The Study Of Rock Physics Model In Tight Sandstones Considering The Effect Of Pore Fluid

More and more researchers pay attention to tight sandstones oil and gas reservoirs recently.Seismic rock physics is a bridge connecting the physical parameters and elastic parameters of reservoir.The establishment of correct rock physics model is very important for the prediction of reservoir elastic parameters.We introduce squirt fluid flow into the thin medium considering the soft pore and stiff pore,and establish a new full-frequency fluid substitution model-double scale model based on the analysis of pore structure,patchy-saturated fluid form,fluid-flow dispersion and single pore structure in patchy saturation model which is not strictly fitted well with practicial pore structure in tight sandstone.This fluid substitution model overcomes the limitation of single pore structure in patchy saturation model and interpretates interaction mechanism between microscopic squirt fluid flow and mesoscopic fluid flow.Then we establish attenuative rock physics model of tight sandstone based on double scale model and the non applicability of effective medium model in tight sandstone reservoir.And we discuss the division of soft and stiff pore aspect ratio and the attenuation effect on elastic parameter.It shows that when the stiff pore is close to the critical value of the aspect ratio between the soft and stiff pores,it will show the characteristics of soft pores,reduce the P and S wave velocity rapidly,and increase the frequency dispersion and attenuation peak.Finally,the prediction value is well fitted with the praticial value,and also the attenuative attribute can indicate the gas position differently in seismic and sonic frequency bands.So we must considere the P wave velocity difference between different frequency bands.At present,we often use the Gassmann model to complete the fluid substitution process in tight sandstone,ignore the interaction of fluid flow between different frequency bands and seismic velocity dispersion and attenuation,and can only establish a single scale rock physical interpretation template.So this paper studys the establishment of multi-scale rock physics template.Based on the established attenuative rock physics model of tight sandstone,we choose the sensitive parameters of porosity and gas saturation and build the rock physics template in different frequency bands.By comparing with the experimental data and the logging well data,we calibrate and verify the multi-scale rock physics model.The physical parameters of acoustic wave and ultrasonic frequency band are used as the input parameters of the rock physics template in the seismic frequency band,which can be used to correct the seismic rock physical template.Finally,the seismic inversion data volume is projected onto the seismic rock physical template to predict the porosity and gas saturation.The results show that the seismic rock physical template can well predict the reservoir physical parameters.