Research On Start-up Limit And Displacement Mode Of Super Heavy Oil Compound Steam Flooding

Ultra-heavy oil is a key part of oil and gas resources.It has the characteristics of high viscosity and high density,which seriously limits the efficient development of ultra-heavy oil reservoirs.Therefore,it is of great significance to explore the recovery mode of ultra-heavy oil reservoirs and to study the formation mechanism and migration characteristics of high oil saturation zones during the displacement process.Combined with the actual situation of the oil field,the development mechanism and related applications of steam injection carbon dioxide in super heavy oil reservoirs are discussed through investigation and analysis,physical simulation experiment research,reservoir engineering calculation,numerical simulation calculation and other methods.Through a large number of literature research,the mechanism of carbon dioxide flooding and steam flooding to increase the formation temperature,reduce the viscosity of crude oil and improve oil recovery is analyzed in many aspects.Firstly,according to the carbon dioxide expansion experiment,the variation law of formation crude oil viscosity,crude oil density,crude oil saturation pressure,crude oil volume coefficient and crude oil shrinkage coefficient with the amount of injected carbon dioxide was studied.In addition,through the thin tube experiment carried out,it was measured that the minimum miscible pressure of CO₂and reservoir crude oil in the study block was 31.9MPa,the original formation pressure was 15.5MPa,and CO₂injection could not form miscible flooding.Secondly,by carrying out high-temperature displacement experiments,the phase permeability characteristics of the steam zone,transition zone and hot water zone of the super-heavy oil reservoir,as well as the reservoir permeability,crude oil viscosity,steam dryness,and the influence of different blocks on the oil displacement efficiency were studied.Based on the high-temperature displacement experiment,the start-up limit and transfer drive limit of super heavy oil steam drive are studied,and the transfer drive limit is determined.The crude oil viscosity is 75000m Pa·s and the permeability is 2500×10^-3?m²,steam temperature 200?,steam dryness 75%.Finally,based on the field test,in the block,the reverse nine-point method is used as the rotary flooding well pattern,the start-up temperature is determined to be 80?,the rotary flooding viscosity is preferably 60000m Pa·s,the permeability is 2000×10^-3?m²,and the oil layer thickness is 10-18m.The numerical simulation results show that the width of high saturation zone in the thermal connection stage in the displacement process is 20m and the oil saturation is 0.62;The width of alternate injection high saturation zone in the displacement stage is 27.6 and the oil saturation is 0.60.The width of high saturation zone in steam flooding is 29.8m and the oil saturation is 0.65;In the denudation stage,the residual oil saturation of carbon dioxide composite steam flooding is lower than that of steam flooding.At the same time,the reasonable injection parameters of steam flooding and carbon dioxide composite steam flooding are determined.The optimal injection parameters of steam flooding are:injection speed of 100m³/d,steam injection dryness of 75%,and production-injection ratio of 1.2;the optimal injection parameters of carbon dioxide composite steam flooding are:the injection speed is 25000m³/d,the injection pressure is 13MPa,the gas-water ratio is 1:1,and the injection period is 0.1a.