Study On The Exploitation Of Multivariate Thermal Fluids For Shallow Heavy Oil Reservoir In Xinjiang Oilfield

Xinjiang oilfield is rich in heavy oil resources,and the characteristics are shallow burial,poor physical properties and high viscosity.At present,the main production mode is steam stimulation,but with the increase of steam stimulation cycles,the oil-steam ratio decreases,the steam channeling is serious and the recovery effect becomes worse.Multi-component thermal fluid?MTF?recovery technology is an effective technology developed in recent years.In oil field,high temperature and pressure MTF?including hot water,steam,CO₂ and N₂,etc?is produced by mixing fuel and air in the multivariate thermal fluid generator and by cooling and mixing outside the generator and injected into the formation for huff and puff.Compared with conventional steam huff and puff,MTF huff and puff has the advantages of wide sweep range,higher oil production rate and obvious simulation effect.Based on the study of the geological development characteristics of Xinjiang shallow heavy oil reservoirs,the rheological and PVT experiments,high temperature and high pressure displacement experiments and huff and puff experiments of Xinjiang heavy oil and its mixtures with N₂,CO₂ and N₂+CO₂ have been carried out.Then the stimulation mechanism of Xinjiang shallow heavy oil production by MTF has been studied.Through reservoir numerical simulation,the influence of injection and production parameters of MTF huff and puff on stimulation effect and gas channeling was studied,and sensitivity analysis was carried out by defining gas channeling coefficient and economic oil-gas ratio.Finally,the geological model of the target reservoir is established to carry out numerical simulation of the actual reservoir,optimize the production mode,optimize the key injection-production parameters,and formulate reasonable criteria for selecting wells and layers for MTF thermal recovery and corresponding injection-production strategies.Laboratory experiments and numerical simulation results show that gas solubility decreases with temperature and increases with pressure.Under the same conditions,CO₂solubility is the largest,followed by N₂+CO₂ and N₂ is the smallest,and N_2,CO₂ and N₂+CO₂can reduce viscosities of heavy oil by 5%?18%,50%?95%and 15%?40%respectively.Hot water+CO₂ flooding has the best effect,with the highest recovery rate of 88%and remaining oil saturation reaching 250?.Water+N₂+CO₂ flooding is the second,and water+N₂flooding was the lowest.The oil recovery rate of MTF huff and puff could reach 1.34-3.88times of cold recovery and 1.26 times of steam huff and puff.The main mechanism of increasing production is reducing oil viscosity by dissolution and heating,expanding heating range,volume expansion and pressurization,foam water plugging,etc.The factors affecting the recovery effect of MTF huff and puff are well spacing,formation thickness,gas injection intensity,gas-water ratio,ratio of high permeability zone and steam injection speed.Finally,the strategy of MTF production in Xinjiang shallow heavy oil is determined.?1?when well spacing is more than 70 m,pure MTF huff and puff can be carried out separately in different heavy oil reservoirs,but gas-water ratio should be reduced appropriately.?2?when well spacing is less than 70 m,?a?In Xinjiang shallow common heavy oil reservoirs?Keqian,Jin003 area,etc.?,steam and multi-component combined huff and puff should be carried out,first steam and then multi-component,and the cycle ratio of multi-component to steam is less than 2;?b?In Xinjiang shallow super heavy oil reservoirs?Hongqian,Hongqian-1-4 area,etc.?,steam and multi-component combined huff and puff should be carried out,and the cycle ratio of multi-component to steam is less than 4.