Fiber-assisted Proppant-carrying Mechansim In Channel Fracturing

Channel Fracturing is a new fracturing technique,which creates a discontinuous proppant placement by alternately pumping proppant-laden and proppant-free pulse.Compared with conventional fracturing techniques,Channel Fracturing can effectively reduce the amount of proppant and improve the stimulation effect.Field practice and laboratory experiments show that fiber can improve the stability of the proppant cluster and reduce the settling speed of proppant,which is the key to achieve Channel Fracturing.At present,few studies focus on the effect of fiber on the proppant transportation and fracturing fluid properties.It results in that technical parameters of channel fracturing could not be quantitatively optimized.Therefore,this paper systematically studied the effect of fiber on settling characteristics of proppant cluster,fracturing fluid rheology,three-phase flow model,fiber-assisted proppant-carrying mechanism and proppant transport morphology.Through dispersing experiment and stabilizing experiment,the basic physical properties of the fibers were analyzed.The results show that the fibers have large aspect ratio,uniform dispersion and chemical stability.In the fracturing fluid,the fibers exist in solid state and the fibers are less in contact with each other.The results of proppant cluster settling experiments show that the effect of fiber is mainly on the proppant cluster stability and settling velocity.The effects of fiber on the microstructure,apparent viscosity and viscoelasticity of Hydroxypropyl guar gum base fluid and gelled fluid were studied.The experimental results show that fiber could promote the formation of the molecular chain network of HPG,which results in an obvious increase in the apparent viscosity of base fluid.And the increment is affected by the fiber concentration,the thickener concentration,the shear rate and the temperature.Because the strength of the polymer chain network of gelled fluid is high,the addition of fiber has a limited effect on it.Therefore,fibers has almost no effect on the apparent viscosity of gelled fluid,but increase its elastic modulus to a certain extent.Based on the discrete element method(DEM)model,considering the fracturing fluid drag force and the contact force of propant and fiber,a fiber motion model and proppant motion model was established.Based on the computational fluid dynamics(CFD),considering the effect of proppant and fiber on the flow of fracturing fluid,a three-phase coupled N-S equation was established.Through coupling these equation,a fracturing fluid,proppant and fiber three-phase coupling flow model was established.The coupled SIMPLE algorithm and explicit difference algorithm were used to solve these equations.The correctness of this model was verified by the particle settling experiment in the fiber-laden fracturing fluid.Using hrec-phase coupling flow model,the fiber-assisted proppant-carrying mechanical was studie by the simulation of single proppant and single fiber settling,single proppant and multi fiber settling,and proppant cluster settling.The simulation results show that the fiber resists the motion of proppant by the physical collision.And the collision is affected by the collision position,fiber orientation,concentration and length.The collision of fiber and proppant would cause the fibers to move,which increase the contact number between fibers.When many fibers contact with each other,a fiber network structure forms,which greatly reduce the speed of proppant.Through the collision with fiber,the shear force of the fracturing fluid to the outer proppant of proppant cluster is transferred to the other proppants,so that the velocity difference between proppants is reduced and the dispersibility of the proppant cluster is weakened.based on the proppant lager-scale transportation experiment,and the experimental results of fracturing fluid rheology,and the results of fiber-assisted proppant-carrying mechanism analysis,the effect of fiber on proppant transportation mechanism was vertified.The experimental results also show that fiber,fracturing fluid and pumping parameters are the controlling factors of channel fracturing proppant cluster shape.Through the comparing of proppant cluster shape and channel characteristics at different flow parameters,the optimal flow parameters were determined.According to it,a chart was established to optimize treatment pumping velocity and pulse timeThis paper reveals the mechanism of fiber-assisted sand carrying,which can provide effective guidance for optimization of treatment parameter,and selection of fracturing fluid,proppant and fiber of channel fracturing.