Productivity Analysis Of Fractured Horizontal Wells In Tight Reservoirs Considering Fracturing Fluid Retention

With the development of horizontal wells and hydraulic fracturing technology,the development of tight oil has become a reality.In view of subnormal pressure characteristics in Changqing tight oil reservoir,the data shows that,a large amount of fracturing fluid remains in the formation,but the production maintains a certain stability and slow decline.At present,it's not perfect of productivity model and productivity evaluation method for this phenomenon.Therefore,it is of great importance to carry out productivity modeling and evaluating of fractured horizontal wells considering flowback and retention of fracturing fluid,in order to provide technical support for horizontal well productivity prediction and fracturing design.The mechanism of low flowback rate and high retention of fracturing fluid is systematically analyzed,and the influence rules for productivity of imbibition and retention is made clear.Two types composite flow model are established respectively,including one considering imbibition and retention of fracturing fluid and threshold pressure gradient,while another considering the mechanism of fractal porosity and fractal permeability.Via Laplace transformation and numerical inversion method,the semi analytical solutions of two models are got.Simulation for fractured horizontal wells is formed,in which,the mechanism of imbibition is characterized by different capillary between matrix and fracture,and complex network is represented by fractal network system.Base on the semi analytical model and simulation method,the influence rules of factors on fractured horizontal wells are analyzed.The simulation considering imbibition and retention of fracturing fluid,as well as productivity predicting method are built up in tight oil reservoirs.The results shows that: the main mechanism of fracturing fluid affecting productivity includes retention,pressuring,imbibition and displacement,etc.;Through mathematical characterization of the above mechanism,the semi-analytical productivity model and numerical simulation method are built up;Productivity increases with the increase of retention rate and imbibition rate,while threshold pressure gradient leading to decrease of production;Fracture heterogeneity is characterized by mass fractal porosity and fractal permeability;The lower mass fractal dimension,the faster decrease of fractal porosity,fractal permeability and crossflow in stimulated region,and the lower productivity;The higher conductivity index,the faster decrease of fractal permeability,and the lower productivity;By matching microseismic events,fractal fracture network system can reflect complex fractures;Simulation results shows that fracture fluid and production increase with the increase of fracture complexity;Finally,it's found that the time of shut down play an important role in fracturing and production,and the optimized shut down time is 10 days under the given condition.The research results can provide theoretical guidance and technical support for the productivity calculation of fractured horizontal wells and fracturing design in tight reservoirs.