Study On The Electrical-acoustic Joint Detection Technique And Simulation Experiment For Gas Hydrate

Gas hydrate is a new energy resources with great potential and widely distributed in the land of permafrost and the seabed sediments.The electrical properties and acoustic properties of gas hydrate reservoirs are the basis of geophysical exploration and resource evaluation.At present,common electrical or acoustic simulation experiments only use a single resistivity or sound velocity to describe the electrical properties and acoustic properties of hydrates,which have certain limitations.But now,the experimental devices based on electrical-acoustic joint detection technology and hydrate simulation experiments can provide more effective technical means for hydrate experimental research.And by measuring the impedance spectrum in a wide frequency range and receiving ultrasonic waveforms,a number of electrical and acoustic characteristic parameters can be obtained,and then a relationship model between characteristic parameters and hydrate saturation can be established which provides data and method basis for the integrated logging interpretation model of electrical and acoustic.A new simulation device was developed which used for the electrical-acoustic joint detection of gas hydrate.Based on virtual instrument technology,a testing system was established,in the hardware part,a new type of electrical-acoustic compound sensor was designed which can realize the overlap between the electrical measurement area and the acoustic measurement area as much as possible,beyond that,impedance spectroscopy measurement technology based on the method of automatic balance bridge comprehensively described the electrical properties of measured medium.In the software part,the measurement and control software developed on the LabVIEW has a high degree of automation and extensibility.It can flexibly control all hardware interface devices and realize the working mode that sensors are excited and data are sampled with a time sharing logic,after completed the preprocessing of the measurement signal,the related physical parameters(such as impedance modulus,sound velocity,etc)were obtained and automatically storaged all experimental data.Utilizing the developed electro-acoustic joint detection simulation device,a simulation experiment of methane hydrate formation and decomposition was conducted and established a set of simulation test and data processing methods for studying the electrical and acoustic properties of methane hydrate loose sediments.Experimental process was analyzed from the aspects of temperature and pressure properties,electrical properties and acoustic properties.The experimental results show that:(1)electrical-acoustic joint detection simulation device can get broadband impedance spectrum and ultrasonic signal,the designed electrical-acoustic compound sensor and its array arrangement and time sharing logic can get the spatial distribution information of characteristic parameters;(2)impedance modulus under different frequencies can be sensitive to detect the point of hydrate formation and decomposition,the impedance modulus show the trend of "up-down-up " with the increased of saturation which match the early stage of hydrate formation plug part pores,the effect of salt removal increased in the medium term,late a large number of hydrate formation and plug more pores;(3)in the process of hydrate formation,the sound velocity in the upper and lower layers of the reactor showed a rapidly increase when the overall saturation was 16.3% and 1.8%,and then slow growth,finally,the sound velocity in lower areas was higher due to generate more hydrate.