Integrated Re-Fracturing Simulation And Energy Enhancement Optimization Of Horizontal Well Group In Tight Oil Reservoir

Staged multi-cluster fracturing of horizontal wells is necessary for tight oil reservoir development but is limited by poor physical properties and large well spacing.It faces problems including rapid decline and low recovery.The combination of horizontal well group re-stimulation,including parent well re-fracturing and infill well drilling is an effective treatment to improve well production and reservoir producing degree.After primary fracturing and a long period of production,the pressure decreases in fractures-control regions,which will make it difficult to propagate for re-fractures in new perforations,and induce the re-fractures to propagate to low-pressure and low-oil-saturation areas,also known as “frac hit”.Injecting water into parent wells can mitigate the problem.However,the stress distribution before re-fracturing,effective temporary plugging technique,re-fractures propagation rules and optimized water injecting strategy are not clear,which limit the promotion of horizontal wells re-fracturing.In this paper,considering the synergistic effects of injection and production,the coupled stress distribution-fractures propagation-productivity prediction models of integrated horizontal well group were established and combined with indoor temporary plugging experiments.Firstly,aiming at the stress distribution before re-fracturing,the induced stresses by single open propped fractures were calculated,and were promoted by line integral method to the complex fractures and corrected based on fractures width changes;the induced stresses by liquids injection and production were calculated considering Fluid-Structure Interaction and using the iteratively coupled method,in which the different change trends of permeability and porosity stress-sensitivity during injection and production activities are separately defined for the first time.Secondly,the indoor temporary plugging experiments were conducted to determine the plugging effect under different conditions including horizontal stress difference,temporary plugging agent combination and pumping rate.It was clarified that the temporary plugging effect was influenced mainly by temporary plugging agent combination,horizontal stress difference and pumping rate mainly influence the propagation rules.Thirdly,based on the re-fractures propagation model,the re-fractures morphology was simulated under different conditions including the degree of depletion,location of perforations,fracture distribution patterns,the timing of water injection,and horizontal stress difference,clearing the re-fractures propagation rules.Finally,based on the re-fracturing productivity prediction numerical model,the liquids production corresponding to different water injection volumes is calculated considering re-fracture morphology;the optimized re-fracturing timing of a single well and well group are also analyzed utilizing an actual well group.Above all,based on the methods of theoretical analysis,numerical simulation,the coupled stress distribution-fractures propagation-productivity prediction models of integrated horizontal well group were established;based on indoor experiments,the temporary plugging condition of horizontal well re-fracturing became clear,achieving the integrated simulation of horizontal well group re-stimulation and water injection strategy optimization to provide scientific references for the tight reservoir development by re-stimulation.