Study On Enhanced Recovery Of Different Huff And Puff Modes Of Low-efficiency Horizontal Wells

The JS field has a complex structure and faults.There is mostly complex fault block reservoirs in this field,and the connectivity of oil layers between these blocks is poor.It is difficult to effectively develop the joint well pattern,and many blocks use horizontal wells to control mining independently.As of now,due to the high water content or the high viscosity of crude oil,among the 54 fault blocks in more than 23 fields of JS,45.5%of the horizontal wells are occupied by inefficient horizontal wells,but the cumulative production accounts for only 15.2%.The horizontal wells are in low-yielding,low-efficiency,high-water-cut mining conditions.In view of the existing problems in the low-efficiency horizontal wells of the JS field,basing on the currently empirical and theoretical evidences of the gas injection huff-n-puff and gas injection huff-n-puff assisted with injecting chemicals,this article takes the ordinary heavy oil reservoir of the Z43 block of JS Field as an example,and refers to the oil of the fault block.Based on the fluid properties of the reservoir,a PVT experiment of the original formation well fluid was carried out and the experimental parameters were fitted.The mechanism of the CO₂'s huff-n-puff was analyzed,and the chemical agent such as water shutoff agent and viscosity reducer assisting gas injection huff and puff.The mechanism of action and its implementation in numerical simulations;Finally,using reservoir engineering theory,fluid phase state experiments,numerical simulation techniques and field practices combined to construct a numerical simulation model for different huff-n-puff modes of low-efficiency horizontal wells.The mechanism and parameter optimization of enhanced recovery of various different huff and puffs were studied.The understanding of the thesis is as follows:?1?PVT phase experiments show that the target well reservoir is a typical ordinary heavy oil reservoir,the volume coefficient of the formation crude oil is small,the expansion energy is limited,and the ultimate recovery rate of exhausted development is low;?2?The experiment of gas injection expansion shows that CO₂ can effectively reduce the viscosity of crude oil,the viscosity reduction effect can reach 25.92%,and it can improve the formation fluid flow performance,achieve "evaporative vapor drive",and CO₂ can reach the area 25m around the wellbore;?3?The laboratory experiment of viscosity reducing agent shows that the viscosity reducing agent can greatly reduce the viscosity of crude oil,and the viscosity reduction effect can reach 98.1%.Through nonlinear viscosity mixing,the effect of reducing viscosity and increasing oil can be achieved in numerical simulation.degree;?4?The water plugging agent reduces the water in the well by molecular adsorption and selective water plugging,and increases the viscosity of the water phase to suppress the flow of the water.However,the water plugging agent may inhibit the flow of the water phase and may also clog the oil phase hole and cause pressure,And reduce the effect of later oil production;?5?In the CO₂ fluxing scheme with injection-viscosity-assisted cohesion,the CO₂ injection amount is 800t,the CO₂ injection rate is 30m3/d,the optimum injection amount of viscosity reducing agent is 800t?molar concentration is 5%?,and the injection speed is 100t/d.Well time 10d,fluid strength 35m3/d,optimal throughput cycle 3 rounds;?6?The optimal CO₂ injection volume for the water-blocking agent-assisted CO₂ stimulation program is 300t,the CO₂ injection rate is 30t/d,the flooding time is 10d,the production fluid strength is 30m3/d,and the optimal injection amount of the water shutoff agent is 100t.?molar concentration is 0.35%?,the optimal throughput cycle is 2 rounds;?7?Different throughput modes of low-efficiency horizontal wells are optimized.In the preferred cycle,the cumulative oil increase of the water-blocking agent-assisted CO₂ stimulation is 1205.8t,and the oil exchange rate is 2.01t/t.The accumulative oil increase of the injection-desiccant-assisted CO₂ stimulation was 1383.05t,and the oil change rate was 0.58t/t.