Study On Carbon Dioxide Fracturing Technology In Tight Reservoir

Tight sandstone oil and gas is a special unconventional energy with great potential for development,which is widely distributed in China.The permeability of the tight sandstone reservoir is low then the industrial capacity only be obtained by hydraulic fracturing.While the conventional water-based fracturing fluid is easy to damage the dense reservoir get low productivity generally after fracturing.CO₂ has the characteristics of strong diffusion,easier to form seam and flowback through the phase change mechanism,therefore,the supercritical CO₂/liquid CO₂ fracturing technology is promising.However,the viscosity of supercritical CO₂/liquid CO₂ is less than one-tenth of the water,the capacity of fracturing or sand carrying is weak and the filter loss is large,so the application is limited.It is necessary to develop thickener to improve its viscosity.In this paper,the temperature and shear resistance of liquid CO₂ before and after adding thickener were tested by laboratory experiment,the results show that the CO₂fracturing fluid system has obvious effect of increasing viscosity,good sand carrying performance,and remarkable drag reduction effect Then,the influence of liquid CO₂ on formation pressure,fluid composition and fluid viscosity was analyzed by numerical simulation,the injected carbon dioxide fluid increases the formation pressure and expand the range of mixed phase;after the formation of reaction,light hydrocarbon mole fraction decreases with time,heavy hydrocarbon gradually precipitation.Finally,based on the above data,the fracturing parameters of the city 2-14 well are optimized.The best design of the vertical well fracturing solution is:well pressure of 5MPa,fracture conductivity of 25³0 D·cm,crack half-length is 120m.This study provides theoretical guidance for the efficient development of tight sandstone reservoirs by supercritical CO₂/liquid CO₂ fracturing techniques.