Development Of A Low-density Proppant For Fracturing In Shale Gas Fields

As a novel non-conventional natural gas,shale gas is getting more and more attention in today's world.In order to achieve industrial development,large-scale fracturing is needed during the exploitation of shale gas because of the characteristics of low-permeability and low-porosity of the shale gas reservoir.During the fracturing operation,proppants are transported into reservoir rock by suitable viscosity fracturing fluid to prop fracture and increase the flow conductivity of fracture.With a high density,normal proppant should be suspended by high-viscosity fracturing fluid,however,the use of high-viscosity fracturing fluid will lead to the heavily residue of polymer in the fracture and reduce fracture's flow conductivity seriously.The use of low-density proppant can decrease the dosage of polymer in the fracturing fluid,in this way,the hurt to shale gas reservoir will be reduced and the production can be improved.In this article,a low-density nutshell is selected as the base material,which will be smashed and grinded ball,and the methods of the soak of phenolic resin and the secondary coated of epoxy resin are engaged to product a low-density proppant for the need of hydraulic fracturing in the shale gas field.The process conditions of phenolic resin and epoxy resin coated are optimized and the best manufacturing conditions are:put nutshell particles into phenolic resin solution under the pressure of 2MPa for 3h,and then put the moist particles into the vacuum drying oven,which has a temperature of 160?,to curing.In this way,the phenolic impregnanted and coated particles are gained.0.15%curing agent is added into the mixture of the phenolic coated particles and 10%epoxy resin and then curing at normal temperature,in this way,the low-density proppant is gained.The density of low-density proppant is 1.17g/cm3,and at the temperature of 25? and 95?,the water absorption of low-density proppant in 24h are 2.26%and 7.21%,and in 48h are 2.54%and 8.72%;Under the pressure of 28MPa and 52MPa,the deformation of low-density proppant are 3.56%and 5.25%,and the breakage ratio are 1.15%and 2.21%,respectively;When the closure pressure of the fracture is 40MPa,low-density proppant has a conductivity of 100 ?m2.cm,which is better than quarta sand.As its low density,proppant can suspend in the fracturing fluid with only 0.15%thickener(guanidine gum),which is much lower than the consumption of thickener of quarta sand and ceramicite.The reduction of thickener in fracturing fluid can decrease the harm to shale gas reservoir.Based on the low-density proppant,a low-viscosity fracturing fluid system is developed in this study.Polyacrylamide is the thickener of the fracturing fluid system and it can be used in this system without crossing linking agent.The formula of this system is:0.3%polyacrylamide(thickener)+1%KC1(anticlaywelling agent)+0.1%DB-80(cleanup additive)+0.1%ammonium persulfate(gel breaker).Texting the temperature and share sustainability of the fracturing fluid system,its viscosity can keep above 50 mPa s for shearing 2h at 95?,proving good temperature and share sustainability;Texting the residue content and the damage to core permeability of the gel breaking liquid of this fracturing fluid system,its residue content is only 40mg/L,much lower than the residue content of guanidine gum fracturing fluid.And its damage to core permeability is between 8.0%and 10.0%,much lower than the industry standard of 30%.In conclusion,a kind of low-density proppant that can be used in the shale gas fracturing is developed in this article.With low density and good application performance,this low-density proppant can meet the needs of shale gas fracturing and has a good application prospect.