Study On The Optimal Design Of Carbon Dioxide Precharged Volume Fracturing

Compared with conventional oil and gas reservoirs,unconventional oil and gas reservoirs have poor physical properties,low porosity and low permeability and it is difficult to have industrial value without fracturing.However,conventional hydraulic fracturing will be caused by water sensitivity to reservoirs,the reservoir is damaged and the development of low-permeability oil fields is reduced.Because of its unique properties of CO₂,this method of fracturing does not cause problems such as clay swelling,emulsification,relative permeability damage and residue,which makes it a good fracturing fluid for low permeability reservoir reconstruction.Therefore,in this paper,a low-permeability reservoir block S in Jilin Oilfield is taken as the object of study.Through reservoir geological modeling and reservoir numerical simulation techniques,the CO₂ fracturing design parameters for the reservoir block are optimized.The well flow model of well S87-7 is established by the phase simulation method.The regression error of each experiment is controlled within 5%and the application conditions are met.The effects of fracturing operations are simulated through single-well and well-group fracturing construction parameters.For single wells with weak inter-well interference,the longer the length of main cracks are and the more secondary cracks are,the better the development effect is and the reasonable crack flow capacity is optimal for development around 30D·cm.For the reverse nine-hole well groups,reasonable crack length of the side well is about180 meters,the reasonable length of the corner well is about 160 meters.The best development effect is about 30D·cm.In addition,the nine well pattern fracturing order is preferred.The fracturing effect in one well network of side well is better than that of the corner well.When the edge wells are fractured at the same time,a certain distance should be ensured and the wells are reduced.Due to pressure-induced disturbances,the optimal fracturing method involves fracturing two side wells simultaneously and simultaneously fracturing three corner wells.The reasonable displacement and injection volume of well S87-13-3 is also optimized.The cumulative oil production do not increase linearly with the increase of displacement and injection volume but it slowed down.The displacement increased to 6m3/min after development,the effect is rather poor,because carbon dioxide energy storage fracturing has the function of replacing crude oil compared with hydraulic fracturing and the increase in displacement and injection volume of CO₂ will weaken this effect leading to a poor development effect.The reasonable injection volume of the well87-13-3 should be around 600m³and the reasonable displacement rate should be around 4-5m³/min.