Petroleum Reservoir Numerical Simulation Of CO₂ Flooding In Low Permeability Reservoir In Block H

Daqing Zijing oilfield is a typical low permeability reservoir.With the extension of waterflood development period and the high water cut stage,the oilfield is faced with a series of problems,the prominent performance of which is the acceleration of water cut rise,the increase of waterflood pressure of injection well year by year,and the obvious decline of oil well production.Due to the difficulty of starting with injected water,CO₂ flooding was adopted to develop the low permeability reservoir in Block H.Laboratory experiments and numerical simulation methods were used to determine the optimal injection and production parameters of CO₂ flooding in the study area.The research results have certain guiding significance for the development of similar oil fields.Firstly,laboratory experiments were carried out in the target block.Oil PVT were carried out,the minimum miscible pressure of formation crude oil was measured by the fine tube experiment,and the relative permeability curve was measured by the unsteady state method with constant flow rate.The experimental results improved the foundation and support for the numerical simulation of CO₂.The experimental results show that the minimum miscible pressure of the target block is 23.2MPa,which is much higher than the formation pressure of 9.5MPa.In this paper,CO₂ immiscible flooding is adopted to carry out relevant research.The relative permeability curve was measured by the unsteady state method at constant flow rate.The experimental results show that the water flooding of low permeability reservoir has obvious characteristics of oil phase permeability,strong heterogeneity,fast water cut rise and fast production decline rate.Compared with water flooding development,CO₂ injection development is more conducive to improving oil recovery,and the recovery degree is more than 12% higher than that of water flooding development.Secondly,based on the study of geological characteristics,fine division of small beds and secondary logging interpretation,the sequential Gaussian simulation method is used to establish the geological model after logging secondary interpretation under the control of sedimentary facies model.The numerical simulation component model of the study area was established based on laboratory experiments,geological models and production dynamics.The historical fitting was completed by combining the development dynamic data with the experimental results of phase permeability,and a numerical simulation model similar to the actual model was obtained.Finally,three different CO₂ flooding development methods were studied,namely continuous flooding,alternate gas-water flooding and intermittent flooding.Considering injection and production parameters such as daily oil production per well,gas injection speed per well,shut-in gas-oil ratio,gas-water slug ratio and slug size,the injection and production parameters were evaluated and optimized by using recovery efficiency,oil increase and oil change rate,and the development scheme of CO₂ flooding to enhance oil recovery in the study area was determined.The results show that the development scheme suitable for the target block is: Under the current water cut condition,the CO₂ gas-water alternating flooding is implemented immediately,and the average daily oil production per well is 2m³/d,the average gas injection rate per well is 10000m³/d,the gas-oil ratio of shut-in well is 1500m³/m³,the slug ratio is 1:2,and the slug size is 3 months,namely 3 months of gas injection and 6 months of water injection.（3）The carbon dioxide numerical simulation results of the test area were put into the numerical simulation model of the block to predict that after 20 years of simulated production,the recovery rate of CO₂ gas-water alternating flooding was 43.86%,with 2,198 million tons of oil produced,and the recovery rate of water flooding was 24.7%,with 1,236,500 tons of oil produced.The recovery rate of CO₂ gas-water alternating flooding was 19.16% higher than that of water flooding.