Research On The Lithoelectric Relationship Of Cave-type Carbonate Reservoirs Based On Artificial Cores

The carbonate reservoir segment,which developed by the dissolution pores and holes,is the hot and difficult point of the reservoir evaluation as the dominant production layer.The development of dissolution holes in different sizes leads to strong heterogeneity of the reservoir,which directly affects the physical properties and conductivity of the reservoir.The development characteristics of natural cores are very complex.core representation and repeatability are poor,so it is impossible to study the characteristics of the solution pores,and the experimental results will affect the accuracy of reservoir evaluation.Therefore,it is of great significance to study the rock-electricity relationship of cave-type reservoirs by making artificial cores to carry out physical simulation combined with the development characteristics of dissolution holes in actual reservoirs.On the basis of full investigation of domestic and foreign scholars' research results,based on the lithology,physical properties and cave development characteristics of Dengying formation in Gaoshiti-Moxi area,the artificial core model of cave type is designed,the manufacturing method of artificial cores and the fabrication of artificial core with different cave diameters were determined.On the basis of this,the influence of cave development characteristics on the rock electric parameters is studied through the rock electric experiment.The main content and conclusions are as follows:(1)Three kinds of vuggy artificial core models of large,medium and small are designed.On the basis of epoxy resin compaction and cementation method,the effects of raw material particle,compaction pressure and binder on the production of artificial core were analyzed by comminution of outcrop carbonate block as raw material.Then,the caved artificial cores were completed by the combination of the sodium thiosulfate.The effects of raw material particles,pressing pressure and cementing agent on the physical parameters of artificial core are not always the same.The higher the pressing pressure is,the higher the binder content is,and the smaller the porosity and permeability values are.When the particle size of raw material changed from coarse to fine,porosity and permeability increased first and then decreased.(2)The total porosity and permeability of the caved artificial core were determined through two basic physical properties experiments before and after making holes,and the porosity of the cave was calculated.The artificial core of cave type can meet the requirement of model design.The NMR results show that the T2 spectrum of the caved core is three peaks,the diameter of the cave increases and the T2 spectrum moves in the direction of the increase,which is consistent with the T2 spectrum of the natural core of the cave type.So,it can be concluded that the two cores have similar pore structure.(3)The cementitious index m values obtained from different cavern characteristic cores vary greatly,and they are distributed between 1.9 and 3.2.When the diameter of the cave is not different from that the dissolved pore,the cementitious index approaches to 2.As a whole,the cementitious index m increases with the increase of the diameter of the cave,and decreases with the increase of permeability.The increase of the saturation index n with the increase of the diameter of the cave and the porosity and the increase of the degree of porosity shows a tendency to decrease with the increase of the permeability.