Micro Characterization Of Pore-Throat Structural And Studies Of Percolation Mechanisms Of Tight Oil Reservoirs

The emphasis and difficulties in the studies of tight oil reservoirs is the micro characterization of its pore-throat structures,which is also the key to its development.In order to comprehensively describe the micro pore-throat structures of tight reservoir,this paper took tight oil reservoirs in the north of Songliao Basin as an example.In L26 and QP2 blocks,the quantitative studies and characterization of pore-throat structures were carried out by a variety of test methods,such as porosity and permeability test,CT scan,mercury intrusion analysis,nuclear magnetic resonance,FIB-SEM imaging,N₂ adsorption analysis.The mechanical sensitivity,fluid occurrence and characteristics of the tight sandstone reservoirs were also analyzed.According to the digital core physical modeling method,the 3D digital core model was constructed by CT and FIB-SEM scanning images,then extracted its pore-throat throat network.Based on the former studies,single-phase flow model and two-phase flow model of pore-throat structures were simulated respectively by the micro scale flow lattice Boltzmann simulation method,which revealed the influence factors of the micro scale flow and fluid flow mathematical model,then simulated and analyzed two phase seepage flow curves.Summarized the mineral types,pore types and pore-throat throat structure characteristics of L26 and QP2 blocks.These two blocks developed a strong vertical lithology continuity,and quartz,plagioclase,calcite and clay minerals were common.The main clay minerals were illite,illite smectite mixed layer and a small amount of chlorite.The work area mainly developed the residual intergranular pores,intercrystalline pores and dissolved pores.L26block cementation was strong,which dominated by calcareous cementation and mainly developed interstitial material filling pore support structure.The average value of the permeability was 0.113mD,the average porosity was 9.6%,and the average pore radius was141.05?m.QP2 block cementation was strong,dominated by calcareous cementation,and mainly with interstitial material filling pore support structure.The average value of the permeability 0.083mD,average porosity was 9.7%and the average pore radius was145.62?m.Uniaxial rock mechanics experiments was carried out to achieved the elastic modulus and Poisson's ratio,which could study rock mechanics and pressure sensitive characteristics.The results shows that,there was a positive correlation between elastic modulus and confining pressure,while the relationship between Poisson's ratio and elastic modulus was not obvious.The modulus of elasticity in L26 block were dispersive,the mean value was 21.65GPa,and the average Poisson's ratio was 0.246.The average elastic modulus in QP2 block was18.09GPa,and the mean value of Poisson's ratio was 0.251.The measured porosity of 9 samples were between 5%-12.1%and the data extracted from digital cores were between 6.14%and13.6%,which shows that extracted porosity and measured porosity were basically consistent.The measured permeability of 3 samples were between 0.042mD and 0.13mD and the simulation permeability were 0.034mD-0.068mD,the extracted permeability and measured permeability were also basically consistent.Analyzed the influence factors of ultra low permeability with the simulation results by lattice Boltzmann.First,infiltration network group with the low probability of connectivity was localized,effective flow between them was not established.Second,the radius of the roaring channel was small,which lead to the high flow resistance along the path,then further reduced the flow capacity.Third,only through the fractures can network groups communicate effectively and thus improve mobility.