Research On Technologies Of Fracturing Proppants

The success of shale gas revolution in America makes hydraulic fracturing technology much more popular.Over the past few decades,hydraulic fracturing has become one of the main technologies due to low cost and increasing production.As a main additive of about 9.5%(volumetric percentage)in fracture fluid,proppants get more and more attention to obtain good goals of environmental protection and higher production.Generally,there are three common traditional types as sand,ceramic and resin coated sand.Nowadays,challenges for proppant research focus on increasing production and reducing the cost by using new technologies.Novel and functional proppants with super high strength,super low density,surface coating modification,self-suspending property or rod-like shape are explored to improve compressive strength,increase permeability and reduce erosion.Our country has a rich reservoir of unconditional oil and gas with special properties of low permeability,low pressure and low abundance which address new challenges for technologies.At the beginning,proppants research and applications are reviewed.Predicted research directions for proppants containing small size,multifunction,high property and smart modification.Chemical surface modification is one of the main points in our research.Due to hydrophobic surface modification of proppants could control water/oil flow,in the first part,particles of sands and ceramics with different sizes,as well as nano silica and carbon nanotubes,are made hydrophobic modification through three different methods:molecular self-assembling,resin wetting and resin coating.Contact angle test,capillary rising,scanning electron microscope(SEM),fourier transform infrared spectroscopy(FTIR),energy spectrum analysis,atomic force microscope(AFM),thermogravimetric analysis and flow test are made characterizations,and the results show a good hydrophobic property.A conclusion is made that the smaller and smoother particles with more-OH groups are easilier modified.In the second part,atom transfer radical polymerization(ATRP)is used to prepare functional nanoparticles and proppants.The modified particles own new properties of hydrophobic or pH responsive.This novel pH responsive proppants can be prepared by hydrolyzing the hydrophobic surfaces,which means that the surface wettability could swich from hydrophilic to hydrophobic,then to hydrophilic.For structural modification,different shapes of proppants,such as 4-legs,8-legs and hollow spheres are designed and prepared.Monte Carlo and EDEM are both used to caculate the porosity of different proppants,by which we get that the porosity increases with more and longer legs.New proppants are prepared by 3D printer and the flow test result can confirm the simulation results.Results from transport simulation show that the new proppants have good permeability and porosity,they also could avoid flow back by legs-acrossing.For physical modification,degradable fibers are used to mix with proppants for enhancing proppants migration.First,fibers with different crystallinity and different size are tested by a series of experiments of thermostability,settling velocity and so on.Then proppants carrying test and flow back test are used to verify the fiber function during the proppants migration.we figure out that the physical modification method by mixing with fibers could improve proppant-carrying capacity for fracturing fluid.