Laboratory Study Of The Elastic Properties Of Carbonate Rocks In Multi-frequency Band

Earthquake measuring petrophysical properties of reservoir rock is built characteristics and seismic response of the bridge.However,the existing petrophysical measurements focused on the ultrasound frequency band,and the actual seismic exploration seismic frequency band used by the existence of a significant difference in the frequency band,and reservoir rock in the seismic response characteristics of different frequencies which also exhibit different characteristics.Therefore,in order to make better petrophysical measurements must be used to guide the seismic exploration seismic reservoir rock band elastic characteristics to measure different sort out different bands velocity,attenuation and other parameters measure the difference between the results and the formation mechanism.Seismic rock physics measurements have obvious regional,lack of a systematic study of the seismic response characteristics for small-scale Carbonate reservoir rock under seismic frequency;relational model experimental results using the system,according to the characteristics of the reservoir rock,pore fluid characteristics,the establishment of seismic exploration,sonic and ultrasonic frequency measurement results of the experiment,the formation of different bands outside data push and fusion method.Due to the lack of multi-band rock physics measurement system as the basis for small-scale Carbonate reservoir temperature,seismic response under high pressure conditions(velocity,attenuation)relationship characteristics and pore fluid characteristics and structural characteristics of the reservoir rock between lack of awareness,making use of existing seismic data using a variety of methods to predict fluid lack of theoretical and experimental guidance.Thus,the basis of experimental results and theoretical systems analysis reveals the fluid reservoir rock with seismic characteristics,will provide the scientific basis for predicting small-scale carbonate rock reservoirs of oil and gas reservoirs and sentenced to identify with fluid type.In order to study the dispersion characteristics of partially saturated fluid,we first study sandstone as the target.The elastic moduli for four sandstone samples are measured at seismic(2-2000Hz)and ultrasonic(1MHz)frequencies.Samples were measured under water-and glycerin-saturated conditions.We observe that the high permeability sample under partially water-saturated condition and the low permeability sample under partially glycerin-saturated condition have little dispersion in the low-frequency(2-2000Hz).However,the high permeability sample under partially glycerin-saturated condition and the low permeability sample under partially water-saturated condition produce strong dispersion in the same frequency range(2-2000Hz).The observation suggested the fluid mobility,defined as the ratio of rock permeability to fluid viscosity,largely controls pore-fluid motion and pore pressure in a porous medium.High fluid mobility permits pore-pressure equilibrium either between pores or between heterogeneous regions,resulting in a low-frequency domain where Gassmann's equations are valid.In contrast,low fluid mobility can produce pressure gradients even at seismic frequencies,and thus cause dispersion.The dispersion curve shows a systematic shift to lower frequencies with decreasing mobility.However,we explored the applicability of Gassmann's theory on sandstone rocks in the context of VP moduli dispersion.Two theoretical bounds for the P-velocity are known,Gassmann-Wood's and Gassmann-Hill's theories.Observation shows how the effect of wave-induced flow controls the transition from the Gassmann-Wood to Gassmann-Hill bounds,and we investigated several rock-fluid mechanisms responsible for this change.In order to profoundly understand the dispersion phenomenon,we have made the frequency dispersion comparison of the carbonate and sandstone under the same fluid.We found that the velocity of sandstones will appear dispersion under water-and glycerin-saturated,and dispersion will be larger with water-saturated.There is no obvious dispersion in carbonate rocks under water-and glycerin-saturated.At the same time,the fluid factor sensitivity coefficients at the seismic frequency and ultrasonic frequency are calculated.It is found that the Poisson impedance is most sensitive to the identification of the fluid in these rocks.Finally,we have fractured carbonate rocks as objects of study,and considered the influence of micro scale cracks on the effective elastic properties of rock firstly.Due to the characteristic frequency of the traditional theory of squirt flow is mainly constrained to sonic logging frequency domain,and the control factor of the characteristic frequency is crack's aspect ratio which is generally a constant value,we can use the rock physical experiment data to extract the rock pore structure characteristic parameters,and based on the which to extend squirt flow model.The extension of the quirt flow model reflects the quantitative relationship among rock elastic properties,fluid properties,pore structure,effective stress and the frequency.We found that the velocity dispersion curve based on the extend squirt flow model fitted well with the experimental data,and also reflected that the squirt flow on the elastic wave velocity can still have a certain effect on the seismic frequency.