Study On The Mechanism And Main Controlling Factors Of Heavy Oil Gas Injection Stimulation In Block G

DG oilfield is a typical heavy oil field in China.The crude oil in the reservoir has high viscosity and poor fluidity.At present,the utilization of reserves in the block is low and the effect of water injection development is poor.According to the above characteristics,huff-and-puff is proposed for the development of target G block.In this study,the high-pressure physical parameters of the target crude oil were tested by physical methods,and the indoor dynamic miscibility experiment was carried out.The gas-oil ratio and viscosity of the crude oil dissolved gas under different injection pressures were tested,and the experimental evaluation of the natural gas huff-and-puff potential of crude oil was carried out.Based on the experimental test parameters,numerical analysis was used to analyze the phase and miscibility characteristics of heavy oil fluid after gas injection.Combining geological data to establish the target block mechanism model,the effects of injection medium and reservoir properties on the huff-and-puff were studied.Finally,based on the chosen injection medium,a single well model was established,and the injection parameters were optimized.Get the following understanding:(1)The test of high-pressure physical property parameters of crude oil shows that the density and viscosity of the ground degassing oil is relatively high and the content of heavy components is high.The dynamic miscibility experiment proves that at the formation pressure,which is 22MPa,when the dissolved gas reaches saturation,the ratio of dissolved gas to oil is 98.0m3/m3,and the viscosity decreases from 2777.5mPa s to 41.76mPa s.(2)Numerical simulation studies on the characteristics of gas phase and miscibility of heavy oil fluids show that the larger the gas injection pressure,the larger the portion of the injected natural gas dissolved into the crude oil,and the greater the decrease in the viscosity and density of the crude oil.The minimum miscible pressure of natural gas injection is about 69.37 MPa,and the gas is injected under the formation pressure conditions,and the miscible flooding cannot be achieved.(3)Numerical simulation results show that the effect of injection of N2 is worse than that of natural gas and CO2.Nitrogen injection is mainly suitable for low-viscosity reservoir mining.For high-viscosity reservoirs,it is suitable for natural gas and CO2 huff-and-puff.For reservoirs with large thickness,shallow depth of reservoir,high viscosity,moderate permeability,and no dip angle,the effect of natural gas injection is better.(4)The preferred parameters for single well natural gas huff-and-puff are:3 cycles of throughput,400,000 square injections,total injection volume of 120×104m3,injection speed of 10,000 m3/d,daily liquid production of 40 m3/d,and throughput cycle of 6 months.The numerical simulation results show that under the optimized scheme,the total oil production after gas huff-and-puff is 4774t,which indicates the oil recovery rate reached 4%,and the oil production increased by 3711t compared to depletion method.(5)The main mechanism of heavy oil injection natural gas throughput and oil absorption is:the injected natural gas interacts with the reservoir crude oil,reduces the viscosity of the crude oil,expands the volume of the crude oil,extracts the light components in the crude oil,forms the internal dissolved gas drive,improve the oil-to-water ratio,etc...