Mechanism Of Micro Seepage In Low-permeability Reservoirs Based On Digital Core

Low permeability reservoirs display such characteristic as narrow pore throat and complicated pore space,rock cementation is poor due to the small overburden pressure in the process of compaction and diagenesis especially in shallow unconsolidated sandstone reservoir,it is difficult to obtain a complete core,this core analysis experiment is time-consuming and error is large,the coring is difficult which is also expensive for deep wells and complex structure wells,physical simulation or experiment is difficult to carry out at the same time,the macroscopic seepage law based on Darcy's law is not applicable to the exploration and development of low permeability reservoir due to micro flow effect produced when the fluid flow in low permeability reservoir,therefore needs to carry out in-depth research on porous reservoir from microcosmic on the scale,such as the topological structure of the pore space,the influence of Pore and throat size on fluid flow,fluid distribution in the interaction mechanism between the fluid,it can fundamentally achieve the reservoir microscopic theory of cognition,in order to find more effective oil and gas extraction technology.Filtering the gray level image,two valued segmentation and connectivity judgment based on the low porosity and low permeability sandstone micro CT scanning combined with the advanced visualization software Avizo and finite element software Comsol,three dimensional fine reconstruction and quantitative characterization of pore parameters are completed.The pore throat structure of the core is studied as the research object,and the porous media is divided into two parts by the removal of the isolated pores and the smoothing of the data surface.At the same time,the surface of the reconstructed data is simplified and repaired,which reduces the time needed for the numerical modeling of the core and the numerical simulation of the micro seepage and the storage space of the computer,the STL file is selected as the interface type of data interaction,and the interaction between Avizo digital core visualization and Comsol finite element simulation software is realized.The simulation of the permeability of pore microstructure,and the numerical simulation of heat conduction at the micro level are carried out based on the image preprocessing and data docking,finally,the application of Avizo and Comsol in the micro seepage and the influence of wettability on the micro seepage of reservoir are investigated,the main achievements and understandings are as follows:(1)The core CT image processing flow is improved,and the two value segmentation of low permeability reservoir rock is established based on watershed algorithm,the pore network model is established based on the image data distance transform to extract the central axis of the connected pores,the porosity,pore throat radius and pore throat area of the core were quantitatively characterized,the accurate description of the micro topological structure is achieved.(2)The seepage simulation of the fluid in the pore space of the core is realized used by the porous medium volume average method based on Navier Stokes equation,the absolute permeability of core is obtained,the numerical simulation method based on digital core is proved to be reliable by comparing the core analysis.(3)The thermal conductivity of four kinds of models,such as non-contact 3D cylinder,non-contact 3D sphere,particle contact 3D sphere and double layer composite,were calculated used by Fourier law based on multiscale homogenization theory,the thermal conductivity of rocks at the micro scale was investigated.(4)The docking of Avizo and Comsol is completed,the visualization of fluid flow in rock is realized,absolute permeability and relative permeability are calculated and the microscopic percolation mechanism of interfacial layer is studied.(5)It is assumed that the degree of water flooding in the pore network model is gradually deepened,and the water saturation increases gradually in the porous media,and then the gas displacement is carried out until the oil content reaches the residual oil saturation used by real 3D pore network based on pore reconstruction and CT image extraction,the effect of wettability on three phase flow in porous media was investigated in view of the different wetting state after aging,the saturation path and the corresponding residual oil saturation of water flooding after three times of water flooding are controlled by the imbibition.