Research On The Effect Of CO₂ Huff And Puff Of Fractured Horizontal Wells In Tight Oil Reservoirs

China has abundant tight oil reserves.Tight oil reservoir has low porosity and permeability.On the basis of horizontal well fracturing,the elastic recovery is still very low,so it is necessary to supplement formation energy.Using waterflooding method to supplement formation energy has the problem of‘no injection,no mining'and waterlogging.Gas injection can make up for the above deficiencies.CO₂ huff and puff is a potential method to improve the utilization rate and recovery degree of tight oil reservoirs.Tight cores from Lucaogou Formation in Jimusar Depression were used to do physical simulation on CO₂ huff and puff alternating elastic mining of matrix-fracture system.The rules of elastic mining,and the factors affecting the elastic recovery were studied.In addition,the influence of injection pressure,injection gas pressure,soaking time,cycle index on stimulation effect of CO₂ injection were studied.Eclipse software was used to conduct numerical simulation to analyze the development effect of CO₂ huff and puff for fractured horizontal wells in tight reservoirs.Combining reservoir numerical simulation and single-factor analysis,the impacts of transfer timing,soaking time,production time,gas injection velocity?gas injection?,and cycle index on the CO₂ huff and puff stimulation effect were studied.The orthogonal test design method that takes into consideration the interactions between various factors was used to optimize the parameters,and three indexes including increasing oil production,oil change rate and oil recovery were comprehensively considered.The optimal combination was obtained by fuzzy comprehensive evaluation.The result shows that timing of injection is after 3 years of depleted mining with gas injection time of 30 days,gas injection quality of 415.8t,soaking time of 30 days,production time of 180 days,and 4 cycles.Under the optimal combination of parameters,oil change rate,single well daily peak production increase rate,daily production rate of single well per day in the throughput cycle and the 10-year recovery rate were 2.912m³/t,1.51,1.16,and 5.865%respectively.The results from above analysis show that the CO₂ huff and puff can improve oil recovery for tight oil reservoirs.