Experimental Study On The Influence Of Pore Structure On Seepage Characteristics In Tight Sandstone Reservoir

Tight sandstone reservoirs with low permeability have poor physical properties and complex pore structures,which makes the seepage characteristics of reservoir fluids obviously different from those of conventional reservoirs.Therefore,studying influences of pore structures of tight sandstone reservoirs on seepage characteristics is significant to improve development and recovery rate of reservoirs.Cores of low-permeable tight sandstone reservoirs from HQ area in Eros are selected in this paper.At first,pore structures are classified by thin sections and scanning electron microscopic,then according to X-Ray diffraction and high-pressure pumping tests,characteristics of pore structures are analyzed.Finally,seepage characteristics with different pore structures are studied by one-phase flow experiments,imbibition tests and Magnetic Resonance Imaging.The following results are obtained:(1)According to the size of pore throats,reservoir space of tight reservoirs in study area is classified into 4 types: large pores,micro fractures,micro pores and mico-nano pores.Large pores are mainly developed chlorite films;micro-fractures are corroded fractures in different minerals,micro pores and micro-nano pores are vugs and intercrystalline pores.(2)Pore structures in study reservoir are grouped into four types: uniform and large pores,stripe large pores and micro-fractures and tight types.Uniform and large pores are the best types of pore structures,they have lots of large pores and they are well sorted,and their porosity and permeability are generally high.The stripe large pores types have concentrated distribution of pore throats,and there are some large pores and wide throats.The wider the fractures of micro-fractures are,the better the physical properties are and the poorer the sorting is.The large pores are distributed scatteredly or rare in tight cores,and they have poorest physical properties;they have the poorest flowing capacity.(3)Damage rates of cores with uniform and large pores on permeability are the lowest,and damage rates of micro-fractures and stripe cores are higher.(4)The differences of pore structures have negligible effects on single-phase gas flow characteristics.The lower the permeability is,the more influence the slippage effect has.(5)The sequence of pore structures from good to poor is: uniform and large pores,stripe pores,micro fractures and tight ones.The better the pore structures are,the lower the heterogeneity,and the better the flowing capacity is.(6)Both the oil and water imbibition efficiency are affected by pore structures.This paper provides a basis for further studying on flowing mechanism of tight reservoir in study area,and builds foundation for later development and improvement of recovery of Chang 6 reservoirs in HQ area.