Experimental Study On Seismoelectric Effect Of Carbonate Rocks In Karst Area

Under the action of elastic energy in porous media containing fluid,the seismoelectric effect is produced by the coupling of mechanical energy and electrical energy.The seismoelectric conversion mainly produced at the solid-liquid interface is closely related to the physical parameters of porous media,and the correlation between them is expected to lead to new geophysical prospecting methods in oil logging and geological prediction.Many scholars have done a lot of research work in seismoelectric logging.Based on previous studies,this paper has carried out a series of seismoelectric experiments on carbonate rocks in karst areas.Firstly,the feasibility of indoor detection of carbonate seismoelectric effect is analyzed theoretically,and a set of seismoelectric measurement system for rock samples for laboratory observation is constructed.Through the seismoelectric comparison experiment of plexiglass and sandstone samples,it is verified that the system can record the converted electrical signals of solid-liquid two-phase seismoelectric interface with high stability and reliability.On-site sampling of carbonate rocks in typical karst areas,processing and preparing rock samples with uniform specifications,and using the seismoelectric measurement system to observe seismoelectric data.The results show that:(1)The seismoelectric signals of moderately weathered limestone and dolomitic limestone are not obvious,and obvious seismoelectric conversion signals are detected at the interface of argillaceous dolomite.(2)By adjusting the source excitation voltage and the distance between the source and the rock sample interface,it is found that the seismoelectric signal is positively correlated with the elastic energy propagating to the interface.(3)By changing the receiving position of the electrode,the seismoelectric signal decreases exponentially as the electrode moves away from the rock sample interface,but the take-off time of the seismoelectric signal tends to be consistent,thus confirming that the transition of the carbonate rock seismoelectric interface under elastic energy disturbance is synchronized to each electrode in the form of electromagnetic radiation,which is also the key to realize the field seismoelectric exploration.(4)Comparing the characteristics of seismoelectric signals of limestone,dolomite and sandstone horizontally,it is found that the difference in porosity of rock samples is the biggest reason for the difference in seismoelectric interface conversion among the three rock samples,which indicates that the seismoelectric effect is sensitive to the pore parameters of rocks,and proves that the seismoelectric characteristics of rocks are expected to represent the physical parameters of rock reservoirs.Based on the indoor measurement results of carbonate seismoelectric experiments,this paper studies the influencing factors of carbonate seismoelectric characteristics from multiple dimensions,and verifies the feasibility of applying seismoelectric exploration to karst exploration in karst areas.On this basis,some beneficial attempts are made for real karst seismoelectric exploration in karst areas.