Study On The Electrical Characteristics Of Carbonate Reservoir Based On Digital Core Technology

Nowadays,there is 60% oil and gas production in carbonate reservoir.Logging responses in carbonate reservoir are affected by space structure,fluid properties and distribution in pore and other factors.Rock physics experiment is a traditionally important study of carbonate electrical conductivity,but it costs much,lasts long and has some problems in obtaining typical fracture core.However,digital core technology can solve these problems well.Based on carbonate 3D digital cores scanned by X-CT,expansion and corrosion operation in mathematical morphology method can be used to simulate the increasing and decreasing of corrosion pores and holes in carbonate reservoir.Closing operation can be used to simulate the fluid distribution in core.Fractional Brownian motion model can be used to set up fracture morphology models with different widths and angles.Then,based on carbonate digital core models with different pore,ho le and fracture morphology,finite element method can be used to carry out the electrical characteristics simulation.There are two part research content: electrical characteristics about pore,hole type carbonate reservoir and fracture type reservoir.For corrosion pore and hole type carbonate reservoir,this paper mainly studies the reservoir in the porosity,formation water salinity,wettability and saturation effect on the conductivity of carbonate rocks.When carrying out rock physics experiment with many digital samples,the result shows that relationship between formation factor and porosity has nothing to do with porosity size,but the pore morphology.Saturation index changes with the increase of water saturation in the carbonate reservoir.Therefore,Archie formula is only applicable for water saturation which is greater than 60% in computing the carbonate reservoir saturation in carbonate reservoir.Compared with oil wet rock,there are more conductive channels in water wet rock with better electrical conductivity,because water phase mainly fills the small pore,but oil phase fills with large pore.Therefore,it is very important to determine the wettability of the rock when calculating water saturation with Archie formula.For fracture type carbonate,this paper mainly studies the influence of different fracture widths and angles on reservoir conductivity.The result shows that with the increase of total porosity,cementation index decreases and saturation index increases in parallel direction of the fracture propagation,but cementation index increases and the saturation index decreases in vertical direction of fracture propagation.Fracture type carbonate reservoir conductivity can be affected by fracture angles extremely,and its anisotropy is strong,so the electrical conductivity is different in the same sample with different directions.Conductive characteristics of different pore and fracture structures and fluid distribution can be obtained and analyzed by numerical simulation of pore and hole type and fracture type carbonate core.According to that,the applicable conditions of Archie formula in carbonate reservoir can be analyzed,which has very important guiding significance to research on the electrical conductivity of the carbonate reservoir.