A Thickener Study For Carbon Dioxide Foam Fracturing Fluids

With the development of the exploitation of the low permeability oil and gas resources,especially water sensitive,water blocking and fractured reservoirs and low pressure reservoirs,the carbon dioxide(CO2)foam fracturing fluid is growing in popularity,because of the good proppant-carrying capacity,the low leakoff coefficient,the low formation damage and the quick flowback.But the present CO2 foam fracturing fluid is still composed of the traditional cross-linked guar gum fracturing fluid,so the flaws of the cross-linked guar gum fracturing fluid are great influence on the superiority of the CO2 foam fracturing fluid,which causes a big damage to the reservoir.Although the VES-CO2 foam fracturing fluid completely solve the problem of the high residue content and the incomplete breaking,the application of VES-CO2 foam fracturing fluid is restricted by its cost and heat resistance capacity.In the research,the C02 foam fracturing technology is combined with the new type non-crosslinked fracturing fluid system.The thickening agent DF is synthesized by the solution random copolymerization,whose monomers are acrylamide(AM),anionic monomer containing rigid groups(SS-n)and Hexadecyl dimethyl allyl ammonium chloride(C16DMAAC).The polymerization condition is preliminarily optimized and the thickening agent DF is analyzed by the infrared spectroscopy,thermogravimetry and dissolution method.The experimental results show that the property of polymer thickener reached a basic theoretical design requirement.On the basis of the thickener agent DF,the formula of the CO2 foam fracturing fluid system is completed to analyze the practical application feasibility of the thickener agent.The liquid of the CO2 foam fracturing fluid prepared by the polymerized thickener agent has a good high temperature and anti-shearing performance.Under the condition of 160?and 170s-1,the viscosity of the fracturing fluid prepared by 0.5%thickening agent still remain stable at 40 mPa·s,and the viscosity value can ensure the enough ability of suspended proppant.At the same time,the outstanding rheological property guarantees the foaming ability and foam stability,the foaming rate is about 325%and the half-life period of CO2 foam reaches 135h in the condition of 30 ?.By testing gel breaking performance and flow conductivity,the CO2 foam fracturing fluid can thoroughly gel-breaking,and its gel-breaking liquid has a lower surface tension and residue content.Therefore,the CO2 foam fracturing fluid shows a satisfactory cleaning property and little damaging of the proppant diversion layer.In this paper,the synthetic thickener is proved that it can be used in the clean CO2 foam fracturing fluid by the theoretical study,experimental synthesis and behavior evaluation.Moreover the clean CO2 foam fracturing fluid can solve the problem stimulating the low permeability oil and gas resources in fracturing technology.Therefore,this paper can provide a new idea in the development to the low permeability oil and gas resources.