| JN oil field is a typical complex small fault-block reservoir,and the differences between reservoir properties are very large,which can be subdivided into thin-interbed reservoir,high-dip angle reservoir and edge-bottom water reservoir.According to the current situation of development,there are no effective well patterns of injection-production in the field,the producing degree of reserve,as well as recovery factor,is poor.The PVT experiments are carried out to evaluate crude oil huff-n-puff potential.Based on geological data,mechanism models are built to study CO2 huff-n-puff process of feasibility evaluation of different reservoir types and mechanisms for simulation in this thesis.The understandings are obtained as follows:(1)The reservoir fluid is a typical black oil,characterized by medium-density,low viscosity,low gas-oil ratio and small expansion.The oil expansion experiments with CO2 injection show that crude oil has a good huff-n-puff potential.When solubility of CO2 is 60mol%,the expansion coefficient is 1.37,and the viscosity-reducing range reaches 76.44%.(2)CO2 huff-n-puff simulation results of the thin interbed reservoir show that the CO2 sweep region is 40m radius around the wellbore.Optimized parameters:injection volume 1000t,injection rate 120t/d,soaking time 18d,cycle period 2.Oil increment of the optimized plan is 1208.15t,average oil change rate is 0.604t/t,recovery factor increases 1.24%,and increasing range is 19.84%.Oil recovery factor of CO2 huff-n-puff is medium.(3)Depletion development of high dip-angle reservoir results show that the gravity is main driving force in mid-late stage of depletion development.Oil recovery by high,medium,and low-position production well increases in the same dip-angle reservoir,in turn.Higher dip angle results in higher oil recovery by low-position production well,maximum recovery difference factor is 1.31%.Low-position production well can make full use of gravity driving to increase oil recovery.(4)The results of CO2/CH4 huff-n-puff of high dip-angle reservoir(30°)show that oil recovery of CH4 huff-n-puff is good,meanwhile CO2 is poor,especially by low-position production well.Optimized parameters:CH4 injection volume 800t,injection rate 70t/d,soaking time 22d,cycle period 3.Oil increment of the optimized plan is 3217.14t,average oil change rate is 1.340t/t,recovery factor increases 2.78%,an increasing range of 26.23%.Oil recovery factor of CH4 huff-n-puff is good.(5)The results of CO2 huff-n-puff of edge-bottom water reservoir show that the earlier timing of injection and lower the rate of water production,the better CO2 huff-n-puff effect.Optimized parameters:injection volume 600t,injection rate 85t/d,soaking time 12d,cycle period 3.Oil increment of the optimized plan is 2118.84t,average oil change rate is 1.177t/t,recovery factor increases 2.77%,an increasing range of 14.05%,oil recovery factor of CO2 huff-n-puff is good.CO2 huff-n-puff can effectively inhibit reservoir water production.(6)Summing up the gas huff-n-puff plans of the three types of reservoirs,time for increasing production of huff-n-puff,which is insensitive to injection rate,is long.Multicycle huff-n-puff to improve oil recovery worsen in turn.The small sweep region is a significant factor affecting the improvement of crude oil recovery.(7)The main mechanisms for huff-n-puff of CO2 as follows:volume expansion of crude oil,viscosity reduction,extraction of light components from crude oil,dissolved-gas flooding.For the edge-bottom water reservoirs,in addition to the above mechanisms,the reduction of interfacial tension between oil and water,increasing mobility ratio and suppressing bottom water cone are also vital mechanisms. |
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