Numerical Simulation Of Reactive Flow In Fractured Carbonate Rocks During Acidization

Acidizing is a widely employed method of stimulating carbonate reservoirs.In fractured carbonate reservoirs,the injected acid can easily travel along the highpermeability natural fractures,resulting in an increased distance of acid activation.Moreover,acid injection can dissolve the rocks,thereby promoting communication between formation fractures.Therefore,the production enhancement effect of acidizing is superior in fractured carbonate reservoirs than in non-fractured ones.However,given the significant heterogeneity in geological conditions across carbonate wells,designing acidizing requires incorporating well data and simulation calculations to determine the specific acid injection scale.Presently,acidizing reaction flow models cannot efficiently handle the complexity of fractures found in actual oil reservoirs.To address this issue,this thesis first models the flow of fluids,transport of solutes,dissolution of rocks,and changes in rock physical parameters during the acidizing process,and establishes a mathematical model for the acidizing reaction flow in fractured carbonate reservoirs.Then,based on an embedded discrete fracture model,the model is numerically solved to develop an efficient method for characterizing natural fractures in the reservoir by separately partitioning the fracture system and the bedrock system.The control equations are discretized using the finite volume method,and the operator splitting method is used to decouple and solve the model.Next,numerical simulations are conducted to analyze the dynamic reaction-dissolution process of acid injection in fractured carbonate reservoirs under 2D linear flow conditions and to investigate the influence of fracture characteristic parameters and pore distribution parameters on wormhole growth dynamics.Finally,a reaction-flow model and numerical solution algorithm for fractured carbonate oil reservoirs considering the influence of temperature are established,and the effects of reaction heat release on dissolution patterns and acid breakthrough volume under different injection rates are analyzed.The findings suggest that increasing initial porosity leads to smaller and more branched wormholes resulting from acid-etched rock,as well as lower acid consumption when acid breaks through the rock core.As reservoir heterogeneity increases,the variance between adjacent porosities widens,intensifying the competition between porosities during wormhole extension and reducing acid consumption.Natural fractures do not affect the etching mode of wormholes generated by acid dissolution or the optimal injection rate of acid during rock acidizing,but they do influence the structure and morphology of the formed wormholes,leading to a reduced acid volume needed for rock breakthrough.Longer natural fractures result in smaller and less branched wormhole diameters and more efficient acid-etched wormhole extension.However,when fractures are excessively long,they interconnect to form a network of fissures,and the wormhole structure only grows along the fractures.Additionally,the direction of natural fractures determines the direction of wormhole propagation,with wormholes primarily extending along the direction of fractures due to their high permeability.When the direction of the fracture is perpendicular to the acid flow,the extension of the wormhole follows the fluid flow and fracture direction,leading to thicker and more branched wormholes.The volume of acid liquid required to breakthrough the rock core increases with the absolute value of the fracture azimuth,reaching its maximum when the fracture azimuth is perpendicular to the acid flow direction.The exothermic reaction can affect the reaction rate of acidrock and therefore alter the generated etching mode.As a result,temperature effects should be considered when conducting acidizing numerical simulations.The numerical simulation method established in this study for acidizing reaction flow can effectively characterize natural fractures in carbonate reservoirs and has important implications for optimizing acidizing design in such reservoirs.