Study On The Three-Dimensional Structure And Pore Permeability Characteristics Of Limestone

Studying the pore structure and permeability characteristics of limestone is one of the important links in analyzing the characteristics of limestone reservoirs.In this paper,taking the Fangezhuang Mine and Linxi Mine in the Kaiping coalfield area as the research object,after collecting relevant rock samples,the lithology characteristics and pore permeability characteristics of limestone were calculated and analyzed by applying experiments such as cast thin sections and high-pressure mercury pressure,combined with electronic computer tomography-CT to extract the three-dimensional micro-structure and related parameters of limestone.The research is as follows:(1)After the casting thin section identification test of the 12 rock samples collected,it was found that the rock samples collected in the Fangezhuang mine and Linxi mine were mainly limestone containing debris and mud crystals.The rock structure is mainly mud crystal structure,and the structure is mainly blocky.The mineral composition of the rock is mainly calcite,but also contains small amounts of dolomite and argillaceous.In addition,the rock has developed structural joints that are fully filled with calcite.(2)After high-pressure mercury pressure experiments on the collected limestone samples,it was found that the porosity range of the mined limestone was 0.33%～9.38%,and the permeability range was 0.0020～0.0106 m D.Among them,FAN5 has the largest porosity,better connectivity,and better permeability;LX1 has minimal porosity,poor connectivity,and poor permeability.In addition,with the increase of sampling depth,porosity and permeability generally showed a downward trend.(3)Using CT scanning technology to obtain rock sample reconstruction data,and then importing it into the 3D visualization software Avizo,the three-dimensional structure and microscopic data of rock samples were extracted,and it was found that porosity was positively correlated with fractal dimension,and pore volume and coordination number were also positively correlated in pore throat structure.(4)The Kozeny-Carman equation was modified and a new permeability prediction model was established.A shape factor was introduced into the Kozeny-Carman equation to calculate the permeability,and a comparison of the permeability data calculated by the model with the permeability data measured by the mercury-pressure experiments showed that the relative errors of them were small.Therefore,the stability of the model was good and it was feasible for predicting the permeability of limestone.There are 81 figures,5 tables and 60 references in this paper.