Study On Seepage Mechanism And Energy Supplement Method Of The Tight Sandstone Reservoir In Northern Songliao Basin

There exist characteristics of worse physical properties,complex seepage law and complicated microscopic pore structure in tight reservoir.With the elastic development of the tight reservoir after fracturing,there are many problems arising such as rapid pressure decline and low oil recovery.There are still few efficient methods for enhancing oil recovery.The dissertation,taking tight sandstone reservoir in Northern Songliao Basin as subject,conducts the research on physical properties,seepage characteristics,imbibition mechanism,seepage law after fracturing and energy supplement in tight sandstone reservoir.The conclusions and acknowledgements are as following:After the experiments of mercury injection,X-ray diffraction,thin sections and sensitivity evaluation,we can determine:The pores of submicron or above contribute more to seepage channels in tight sandstone reservoir in Northern Songliao Basin.There is medium level or lightly stronger in water sensitivity,salinity sensitivity and stress sensitivity.There is weaker impair content in velocity sensitivity,and alkali sensitivity and acid sensitivity.Inter-granular pores mainly exist in FY reservoir,and intra-particle pores mainly exist in GTZ reservoir.The latter is more brittle than the former.It shows an obvious performance of non-linear seepage characteristic in tight sandstone reservoir.As the water saturation increases,oil-water pseudo-threshold pressure gradient first rises and then declines.A new mathematical model for two-phase pseudo threshold pressure gradient,core permeability and water saturation is established.On that basis,a new formula for calculating oil-water relative permeability of tight reservoir is deduced.For the tight sandstone reservoir in Northern Songliao Basin,the relative permeability curve shows characteristics of two high parameters and two low parameters.Two high parameters are irreducible water saturation and residual oil saturation.Two low parameters are water permeability and oil recovery.The oil permeability declines rapidly which result in the narrower span of two-phase seepage.Therefore,it is hard to injection water to enhance oil recovery.The existence of fractures helps enhance seepage and development effect.It is necessary to supple formation energy in time to avoid stress sensitivity of fractures.In order to study the huff-n-puff mechanism on the field,an apparatus and methodology of static imbibition and dynamic huff-n-puff process is created.The designed apparatus makes it possible to simulate two simulation processes of static imbibition and dynamic huff-n-puff.There are certain factors,which are imbibition solvents,fracture and wettability,influencing oil recovery significantly.So the optimization of such factors is the best way to enhance oil recovery.Surfactant water and fracture help enhance oil recovery.On contrast,the filtrate of fracturing liquids does not.Therefore,it is recommended that the flow-back time of fracturing liquids should be shortened.NMR technology is combined with imbibition method to determine the mobilization limit of different injection solvents in tight reservoir.The pore size that can be mobilized by CO₂ should be above 0.05?m in GTZ and FY reservoir.In contrast,the pore size that can be mobilized by surfactant water should be above 0.1?m in GTZ and FY reservoir.Fractures'influence on seepage rule and development mechanism is studied with a new designed apparatus for large 3D core models under the condition of high pressure and temperature.Different zones form during the process of seepage in tight reservoir.They are effective swept zone,weak swept zone and ineffective swept zone.The main development mechanism after fracturing is to enlarge weak swept zone and imbibition area and to increase the pressure gradient of effective swept zone.In the meanwhile,CO₂ is chosen as the optimum injection solvent to be injected into tight reservoir.As the results of numerical simulation study of typical well block show,CO₂ huff-n-puff achieves a good performance in enhancing oil recovery.The rational amount of CO₂injection is 7500t with the injection rate of 180t/d.The soaking time is 30 days.The results provide guidance for the oil production on the oilfield.We have witnessed good performance in enhancing oil recovery of 4 experimental wells.The dissertation determines the seepage characteristic and physical properties of tight sandstone reservoir in Northern Songliao Basin.Imbibition mechanism is elucidated in the process of dynamic huff-n-puff.CO₂ is chosen as the optimum injection solvent for energy supplement.The results provide technical support for efficient development on the field.