Study Of Experiment Of Stress Effect On Longitudinal Wave Velocity Of Simulated Cementation Hydrate Core

As a new clean energy, natural gas hydrate is of growing concerned. Toaccurately obtain the gas hydrate position formation and the reserves information hasbecome key to natural gas hydrate resource development. Research on core andlogging data which can reflect the natural gas hydrate reservoir accurate informationhas become the key to exploration and development of natural gas hydrate, and basison core and logging data is the velocity of gas hydrate. The main effect of hydrateacoustic velocity of is the saturation of hydrate formation. In the process of drilling,disturbance around the wellbore formation will affect the acoustic velocity of hydrateformation, in order to solve this problem, this paper carried out a series ofexperiments on the cementing state hydrate model compression stress-wave velocity.The longitudinal wave velocity of hydrate samples is an important index of itsacoustic parameters, can indirectly reflect the important properties of hydrate storagestructure, distribution, saturation. But when measuring the acoustic parameters ofhydrate samples, the experimental conditions can have an important impact on theexperimental results, therefore, before measuring the acoustic parameters of hydratesamples acoustic parameters, calibrated experiment must be carried out, in order toimprove the accuracy and reliability of experimental results. External controllableconditions and reactor required in laboratory synthes of hydrate samplesis is thestarting point, deeply studied on the factors affecting the measurements of acousticparameters of hydrate samples. The study found the different structure parametersabout container, the different frequency of the transmission and different excitationvoltages has great impact on ultrasonic. Container bottom thickness is smaller,transducer frequency is larger, the excitation voltage is higher, mostly in favor ofultrasonic propagation and obtained the first wave in experiments.Through optimizating the structure parameter of the container, controllingexternal experimental conditions, in the premise of ensuring the accuracy ofexperimental results, in order to control the magnitude of the load and the saturation of cementing state hydrate sample, we carried out series of experiments on thecompressive stress-velocity. The study found pressure, saturation can has an impacton longitudinal transfer of hydrate core. The experimental results show that:(1)The longitudinal wave velocity of cement hydrate samples with differentsaturation state are increased with increasing compressive stress. During theexperiment, with the increase of compressive stress, simulation core skeleton particlescompacted, dislocated, resulting in the decrease in porosity, facilitates thetransmission of ultrasonic wave velocity increases with stress.(2)For a certain saturation samples, when the pressure is small, the velocitychanges little with increasing pressure, when the pressure reaches a certain value, thevelocity amplitude increases with increasing stress, when the pressure will continueto increase, the velocity increases along with the pressure increases but the change isnot large. Analysis can be found that for the cementing state hydrate simulation core,when the pressure is small, the destruction of their internal pore structure cannot bedamaged, so the velocity increases along with the pressure is not significant; when thepressure reaches a certain value (critical value), the pore structure was severelydamaged, variation of velocity with increasing pressure is larger, then the core samplepore structure was completely failure, core porosity, saturation change are small, sothe velocity variation with pressure is small.