Study On The Mining Mechanism And Adaptability Of Multi Thermal Fluid In Heavy Oil Reservoir

This study aims to solve the problems of high viscosity of crude oil,poor cold production effect,low production rate of reserves and low oil recovery in the development process of offshore heavy oil reservoirs.The effect of multicomponent to physical property of typical crude oil is firstly investigated through laboratory experiment.The results show that the solubility of multicomponent in crude oil decreased with the increase of crude oil viscosity and the solubility of multicomponent in crude oil decreases with the increase of temperature.The volume coefficient of oil/gas mixture increases with the increase of dissolved gas oil ratio.Under the condition of unchanged dissolved gas oil ratio,the volume coefficient of oil/gas mixture increases with the increase of temperature.The effect of temperature on viscosity reduction of crude oil is better than that of multicomponent,and the higher the crude oil viscosity is,the more obvious the characteristic is.At different temperatures,the contribution rate of viscosity reduction of temperature is higher than that of multicomponent,and the higher the temperature,the lower the contribution rate of multicomponent.Then the water displacement experiment research of heavy oil with different viscosity was carried out,and the recovery efficiency of polymer flooding,hot water flooding and active water flooding were also contrasted after water flooding.The water cut of water-multi thermal fluid alternate displacement was optimized through physical simulation and the viscosity limit of multi thermal fluid huff and puff was also confirmed.The experimental research of multi thermal fluid displacement was carried out under condition of different oil viscosity,different formation pressure and different gas water ratio respectively.The results show that the viscosity limit of water flooding should be less than 350mPa?s,polymer flooding can be selected as a strengthened water flooding method at low crude oil viscosity and multi thermal fluid flooding can be selected as a strengthened water flooding method at high crude oil viscosity.In order to obtain a higher final recovery rate,the water cut of water-multi thermal fluid alternate displacement should be as low as possible.The multi thermal fluid displacement will not have a good effect if the crude oil viscosity is higher than 10000mPa?s.The optimal gas/water ratio of multi thermal fluid displacement is 1.5:1?underground?.The conversion pressure of multi thermal fluid displacement to multi thermal fluid huff and puff is suggested as 4⁵MPa.At last,a heavy oil reservoir with was selected as research object.The injection production parameters of different development stages for the multi thermal fluid huff and puff,the conversion time of multi thermal fluid huff and puff to displacement,the well pattern of multi thermal fluid displacement and the injection produciotn parameters of dfifferent development stages for the multi thermal fluid displacement were all optimized through numerical simulation.The results show that the process of multi thermal fluid huff and puff can be divided into three stages:early stage,medium-term stage and late stage.As development progresses,the intensity of water injection increases first and then decreases;the gas water ratio slightly increase first and basically remain unchanged at medium-term stage.Finally,it increased gradually at late stage.The proportion of CO₂ in gas is higher at early stage and then decreased gradually.The proportion of CO2 in gas is maintained at about 40-60%at early stage and is maintained at about 15%at late stage.The optimal time of conversion of multi thermal fluid huff and puff to multi thermal fluid displacement is the time when the formation pressure is reduced to 4-5MPa.The optimal well pattern of multi thermal fluid displacement is five-spot pattern.There are 3 stages in the process of multi thermal fluid displacement,that is:the low water cut stage with a water cut less than 40%,the rising period of the water content with a water cut of 40%-80%and the high water cut stage with water content greater than 80%.As development progresses,the gas water ratio increases gradually,the proportion of CO₂ in gas and the water injection rate all decrease gradually.