Investigation On The Law Of Depletion Recovery And Gas Injection Huff-n-puff In Tight Oil Reservoir

Tight sandstone oil reservoirs have become an important part of the oil and gas resource in china with the incrensing demand for oil and gas.Compared with conventional oil reservoirs,Xinjiang 's tight oil reservoir has abundant reserves and great development potential.However,due to deep burial,high temperature and pressure and complex pore structure,the law of depletion development and its influencing factors are not clear.The depletion recovery is low,and residual oil content is high during elastic depletion.Moreover,it is difficult to enhance oil recovery by water injection wiht poor injectivity and effect,and cause irreversible damage to the formation.CO2 huff-n-puff and N2 huff-n-puff can effectively improve the recovery degree of low permeability and ultra-low permeability reservoirs,but whether it can effectively improve the recovery degree of tight oil reservoir remains to be studied.Therefore,to correctly understand the micro-pore structure of tight sandstone oil reservoirs,establish a physical simulation experiment of elastic deplement in tight reservoirs,analyze the influence of different factors on the elastic depletment effect,study the factors influencing the effects of different injected gas huff and puff,investigation the characteristics of remaining oil production,evaluate the feasibility of gas injection huff and puff,which are important for the efficient development of tight sandstone oil reservoirs.At first,the thin section,helium porosity tester,polarizing microscope and scanning electron microscope were used to qualitaticely characterized the lighology,physical properties and storage space characteristics of tight sandstone reservoirs.The tight oil reservoirs are classified into fracture cavity type,pore type and non-reservoir with little development value according to the characteristics of capillary pressure curves obtained by high pressure mercuty intrusion.The pore throats in tight oil reservoirs are divided into nanometer pore throats,micro-nanometer pore throats and micrometer pore throats according to the results of NMR test.However,the pore structure of the reservoir was quantitatively characterized according to the results of micro-nano-CTSecondly,based on the improve high-temperature and high-pressure depletion exploration emperimental device,a series of indoor physical simulation experiments were conducted to investigate the depletion recovery law of tight oil reservoirs.The influence of factors such as production pressure,permeability,viscosity,and gas-oil ratio on the degree of depletion recovery were analyzed,according to the experiment results,and a prediction model for depletion recovery of tight oil reservoirs was established.However,the fluid distribution under different conditions was measured by NMR tests and the charcateristics of oil production in micro pores during depletion exploitation of tight reservoirs was analyzed.Thirdly,a series of indoor physical simulation experiments of CO2 huff-n-puff were conducted on the basis of depletion recovery.The law of CO2 huff-n-puff and the influencing factors such as huff-n-puff cycle,production pressure,permeability,viscosity,and soaking time on the CO2 huff-n-puff,the feasibility of CO2 huff-n-puff in tight reservoirs were analized according to the results.The mechanism of CO2 huff-n-puff EOR was analyzed from the microscopic point of view,and the characters of the oil production distribution in different pore sizes during CO2 huff-n-puff were analized by meaureing the residual oil distribution in different huff-n-puff cycles with nuclear magnetic resonance technology.Finally,on the basis of depletion experiment,a series of indoor physical simulation experiments of N2 huff-n-puff were conducted to invitaigate the influencing factors N2huff-n-puff such as the huff-n-puff cycle,production pressure,permeability viscosity,and soaking time.Then,by comparing and analyzing the feasibility of improving the recovery degree of CO2 stimulation and N2 stimulation in tight oil reservoirs was determined through comparative analysis.