Rock Physics Modeling And Broad-band Experimental Measurement Of Carbonates

The major reservoir rocks of oil and gas fields around the world are carbonate rocks.Due to the effects of groundwater erosion and dolomitization,carbonate rocks often exhibit complex microstructure characteristics.The complex microstructure of rock has a direct impact on the speed of seismic wave propagation and the energy attenuation of seismic waves.Conversely,it also provides us the possibility to invert the microstructure of the rock,the type of the pore fluid,etc.from the velocity and attenuation of the seismic wave.In this paper,low-frequency rock physics experiments and theoretical modeling analysis are carried out for the Dengying Formation dolomite in the Sichuan Basin and the Ordovician limestone in the Tarim Basin,Xinjiang.The purpose is to clarify the influence mechanism of the microstructure and pore fluid properties of the carbonate reservoir on the dispersion and attenuation of seismic wave velocity.The main contents of this paper include: improving the low-frequency rock physics experimental measurement system,measuring the velocity dispersion and attenuation of carbonate rocks in the seismic frequency band,constructing a physical model of dispersion and attenuation suitable for carbonate rocks and comparing experimental data for analysis.Based on the use of strain gauges as sensors,we experimented the distributed feedback laser sensors in measuring dynamic small strains.The accuracy of the nano strain is compared with a conventional strain gauge sensor.In rock experiments,the collected carbonate samples were first classified according to the results of thin sections,electron microscopy,and CT scans.Then the dispersion and attenuation of saturated fluids in different pore types of carbonates were measured.The difference of dispersion and attenuation behavior caused by pore type and the influence of confining pressure on dispersion were obtained.The experimental results are compared with the squirt flow model considering the aspect ratio distribution and intermediate pores.It is considered that the model can better explain the dispersion behavoir in the seismic band for crack and fracture-pore carbonate measurement results.At the same time,the high frequency experimental results are compared with various effective medium models and fluid saturation models.It concludes that the Gassmann equation has good applicability to carbonate rocks under certain conditions.This thesis mainly included:(1)A DFB-strain gauge cross-band rock physics measurement system is built in the laboratory,which enriches the measurement method of using the core-scale reservoir rock samples in the laboratory for seismic frequency bands.(2)The paper studies the effects of frequency,reservoir pressure,pore fluid and pore structure on the dispersion and attenuation of seismic waves propagating in carbonate rocks;(3)Data from cross-band rock physics experiments of fluid-saturated carbonate rocks can be used to test theoretical models,extending the understanding of the dispersion and attenuation mechanisms of carbonate reservoirs.In summary,this thesis conducts experimental research on the centimeter-scale carbonate rock samples through the cross-band measurement system constructed in the laboratory,enriching the experimental data related to the middle and low frequency bands of carbonate rocks,and also providing support the theoretical model,geophysical inversion and reservoir description.