Experimental Study On The Feasibility Of Artificial Foamy Oil Enhanced Gas Mixture Huff-n-Puff Method In Heavy Oil Reservoir

Cyclic solvent injection(CSI)has a wide range of applications after heavy oil primary production.However,the principal limitations with this process are a quick solvent liberation due to the high gas mobility and oil viscosity regainment during the production period.In this paper,by combining the foaming properties of oil-soluble surfactant and reducing the viscosity and the volume expansion of heavy oil caused by gas mixture(produced gas and propane),we study the method of artificial foamy oil enhanced gas mixture huff-n-puff method,and try to solve the limitations of conventional cyclic solvent injection.A series of long core huff and puff tests were carried out by using a specially designed long core gripper to inject oil-soluble surfactant slug and gas mixture slug composed of produced gas and propane respectively after heavy oil primary production.The tests verified the feasibility of enhancing the recovery of heavy oil reservoirs in the late stage of heavy oil cold recovery by using artificial foamy oil enhanced gas mixture huff-n-puff,as well as the influence of gas composition,pressure depletion rate,wormhole and confining pressure.Finally,micromodel tests were carried out to observe the characteristics of gas bubbles flow in the process of artificial foamy oil enhanced gas mixture huff-n-puff.In this paper,a specially designed long core experimental device was used.First,the experiments of cyclic produced gas injection,cyclic gas mixture injection experiments and artificial foamy oil enhanced gas mixture huff-n-puff were carried out.By comparing data of recovery factor,gas-oil ratio and gas utilization rate of three kinds of experiments,it is verified the feasibility of artificial foamy oil enhanced gas mixtuer huff-n-puff after heavy oil primary production.The effect of gas composition,pressure depletion rate,wormhole and confining pressure on artificial foamy oil enhanced gas mixture huff-n-puff is studied.The flow characteristics such as migration,coalescence and splitting,as well as the diameter,number,stability and liquid film thickness of gas bubbles in cyclic solvent injection,cyclic gas mixtre injection and aritificial foamy oil enhanced gas mixture huff-n-puff experiments were analyzed.The microcosmic mechanism of aritificial foamy oil enhanced gas mixture huff-n-puff was analyzed.The experimental results show that the aritificial foamy oil enhanced gas mixture huff-n-puff process can create effective foamy oil phenomenon in heavy oil,which contributes to gas dispersion in the oil that delays the formation of free gas.The most efficient test improves oil recovery by 45.34%compared to the cyclic produced gas test,indicating that the artificial foamy oil enhanced gas mixture huff-n-puff process is a feasible method for heavy oil recovery after primary production.There is an optimal C₃H₈ content in solvent mixture,which will achieve maximum solubility and generate effective foamy oil flow.The gas mixture should be injected at or near to its dew point conditions without any liquefaction,and make the process more economical.Increasing pressure depletion rate and confining pressure are beneficial for artificial foamy oil enhanced gas mixture huff-n-puff processes to enhance oil recovery factor in short production time,but results in lower final oil recovery factors.The presence of wormhole increases the amount of gas mixture dissolved in the heavy oil and the contact area between oil-soluble surfactant and heavy oil,creating an effective foamy oil mechanism.The micromodel tests show that foamy oil phenomenon persists throughout the artificial foamy oil enhanced gas mixture huff-n-puff process,and there are abundant gas bubbles during the mircomodel tests,and the gas bubbles stability is high and the diameter is small.