| The diversity in scale,distribution and connection of fractures and vugs in fractured-vuggy carbonate reservoir makes the fluid flow extreme complex,especially for the multi-phase flow in this medium.So it is critical and imperative to investigate multiphase flow law for theoretical foundation for efficient and sustainable oilfield development.In this dissertation,the fundamental theory of two-phase fluid flow in fractured-vuggy medium is investigated through various physics simulations,including oil-water two phase flow,oil-gas two phase flow,water drive,and gas flooding test.Firstly,a series of fractured-vuggy models were designed and produced according to the characteristics of geology and fluid of a typical fractured-vuggy reservoir in western China,including models of single fracture,fracture-vug medium,fracture-vug unit,and discrete fracture-vug model.With the combination of experimental visualization techniques,system of automatic data collecting and recording,and measurement technique of sensor,the systematic experimental apparatus and measurement method were formed for the two-phase fluid flow study.Secondly,the oil-water and oil-gas two phase flow through fracture and fracture-vug medium model were conducted,and the flow patterns for these experiments were divided through observation.The channel flow of oil-nitrogen appeared in fracture-vug medium is not as stable as that in single fracture.But the channel will become more and more non-interfering and stable with the increase of vug quantity.The homogeneous phase flow model with considering flow pattern was established though fitting experimental results.S-shaped curve of gas phase relative permeability in the fracture-vug medium model performed more obvious with the decrease in capillary number.Thirdly,in order to have a better understanding of oil-displacement in the basic unit of fractured-vuggy medium,the water and nitrogen gas flooding test were conducted on single fracture and fracture-vug unit model.The channeling coefficient was adopted to depict the degree of water and gas channeling in fracture,and the prediction model of channeling were obtained by fitting experiment data for water and gas drive separately,which can be used to predict the channeling degree for certain fracture aperture and displacement rate.The displacement test in fracture-vug unit model shows the dominated role of gravity in both water and gas drive process.When displacing along the level direction into a standing fracture,there existed an optimal injection rate for water flooding,however,the larger injection rate is the better displacement efficiency is during gas injection process.Fourthly,through the derivation of advancement equation of water-oil displacement front in fracture-vug unit and assuming the similarity is reached if the advancing velocity is proportional between model and prototype,five dimensionless numbers were obtained for similarity analysis in discrete fractured-vuggy medium,that is gravity number,ratio of flow capacity between fracture and fills,vug filled degree,dimensionless vug height,and viscosity ratio of oil to water.The results of the bottom water drive test in 2-D discrete fractured-vuggy model shows the adverse effect of vug filling,which aggravates the pre-existed heterogeneity of reservoir,in particular for the fracture-developed stratum.A mathematic model was established by using modified Dykstra-Parsons method for bottom water drive dynamic prediction.The calculation results show the strong influence of the “heterogeneity” of fracture system on oil-displacement.Finally,according to the gas flooding test in fractured-vuggy medium,the oil-gas gravity segregation shows dual characters.First,the injected nitrogen gas can tap effectively the remaining oil after water drive.However,the gas would channel through corridor existed in the top of reservoir,which would cause a poorer sweep efficiency.But the vug filling can improve the performance of gas flooding to a certain extent. |
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