Experimental Study On Viscosity Reducer And Gas Assisted Cold Recovery Of Deep Extraheavy Oil

With the continuous exploitation of oil resources the world’s oil reserves are decreasing,especially the high-quality and easy to recover oil reserves.In proven oil resources,heavy oil accounts for an increasing proportion.Effective development of heavy oil resources is an important means to alleviate the energy shortage situation.At present,most heavy oil reservoirs are developed by thermal recovery,which has the problems of sand production,gas channeling and high cost.Heavy oil cold recovery technology can effectively improve the utilization rate of oil and gas resources and control the economic cost.Therefore,it is significant to study the EOR mechanism of heavy oil cold recovery.In this paper,we tested the physical properties of the original heavy oil and selected oil-soluble viscosity reducer with good viscosity reducing performance and stability.Then we analyzed the viscosity reduction mechanism of oil-soluble viscosity reducer.In addition,we studied the influence of temperature,viscosity reducer concentration and gas type on the migration characteristics of foamy oil through microscopic visualization experiments and analyzed the factors affecting the stability of foamy oil.Then,we studied the influence of viscosity reducer concentration and gas type on heavy oil recovery and analyzed the mechanism of enhancing heavy oil recovery through huff-n-puff experiments.At last,we carried out the field test.Oil-soluble viscosity reducer can significantly reduce the viscosity of extraheavy oil.The viscosity reduction efficiency of viscosity reducer Y-14 can reach 86.78%at 5 wt%.The oil-soluble viscosity reducer can disperse the aggregation state of the asphaltenes in the heavy oil and decrease the size of the asphaltene particles.The internal friction between the particles has decreased,so that the flow resistance of the heavy oil decreases,thus achieving the purpose of reducing the heavy oil viscosity.The viscosity reduction effect of the oil-soluble viscosity reducer on the extraheavy oil is irreversible,and the viscosity cannot again increase.When CO₂is used as dissolved gas,the bubble formed has the best stability,the maximum flow velocity and the highest recovery.The effect of CH₄as the dissolved gas is slightly inferior to that of CO₂and the effect of N₂as the dissolved gas is the most inferior.With the increase of the temperature,the bubble velocity and oil recovery factor are considerably increased.Adding oil-soluble viscosity reducer into heavy oil can significantly improve the recovery rate of heavy oil and make the phenomenon of foam oil more obvious in the produced oil.When the concentration of viscosity reducer was same,the effect of CO₂huff-n-puff was slightly better than that of CH₄,but the oil/gas exchange ratio of CH₄is significantly higher than that of CO₂,so comprehensive consideration should be taken in the field test.In addition,the field test results shown that oil-soluble viscosity reducer assisted natural gas huff-n-puff can effectively exploit deep heavy oil reservoir.