| Tight oil resources are abundant in China,which is one of the important oil replacement resources,can be developed by volume fracturing technology.The on-site monitoring and experimental results indicate that the geometry of fracture networks after large-scale volume fracturing is complex,and existing research is difficult to fully characterize the three-dimensional(3D)fracture network characteristics such as curved fractures and interlayer penetrating fractures.There is also no semi analytical method for rapid prediction of oil,gas,and water three-phase production under complex fracture network conditions.This thesis focuses on the characterization of 3D fracture networks and multi-phase flow in tight reservoirs and conducts research on the characterization of3 D fracture networks after fracturing in tight reservoirs,the analysis of 3D fracture network transient pressure in the early production stage,and the prediction of multiphase production in the middle and later stages of production.Firstly,considering the effects of stress,natural fractures,and interlayer,the propagation of 3D fracture networks was analyzed.And the discrete fracture method constrained by interlayer was employed to characterize the geometry of 3D fracture networks in the single layer and multi-layer condition.By combining the discrete fracture finite volume approach and the 3D source function,a single layer 3D fracture network single-phase flow mathematical model was developed.A 3D fracture networkmatrix coupling single-phase flow mathematical model suitable for the early stage fixed liquid production of multi-layer reservoir was established,laying the foundation for the fracture network characterization method for the multiphase flow mathematical model,when combined with the parameter dimensionless method taking into account the longitudinal heterogeneity of the reservoir.Furthermore,based on the effective characterization of the 3D fracture network,a multi-phase production prediction method for fracture units considering fracture closure and stress sensitivity was developed for the fracture element,combined with the three phase(oil,gas and water)dynamic drainage area,reservoir zoning,and material balance equation.Then,coupled with the numerical solution of multi-phase flow in discrete fracture networks,a mathematical model for oil,gas,and water three-phase flow under complex fracture network conditions in the mid-term of oil well production was established.A multi well interference fracture unit was proposed in response to the problem of multi well interference produced by measures such as well network encryption in the later stages of production,and the connection impact of nearby well fractures was simplified to a regular fracture connection region.A multi-well multiphase seepage mathematical model that takes into account inter-well interference was developed.Finally,the features of unstable flow in different stages of production of 3D fracture network oil wells and on-site applications were studied.Typical well testing curves of single-layer and multi-layer 3D fracture networks were drawn and analyzed for the early fixed liquid production stage,and eight flow stages were divided,which were different from conventional planar fractures in the early linear flow and radial flow stages of fractures;due to the influence of interlayer flow,there were obvious indentations in the early stages of multi-layer 3D fracture network well testing curves.The production performance characteristics of the stereoscopic fracture are analyzed,and the corresponding orthogonal fracture model is established based on the production of typical wells in Daqing Oil Field,and the reservoir and fracture parameters are interpreted through production matching.A quantitative evaluation of inter-well interference was achieved by combining genetic algorithm and production prediction model for multi-well production in shale reservoirs in southern Canada.The fracture network characterization method,mathematical model and fracture parameter interpretation method of tight reservoirs after large-scale volume fracturing studied in this thesis have developed and improved the percolation theory of volume fracturing fracture network of unconventional oil reservoirs,providing theoretical basis and practical guidance for efficient development of unconventional oil and gas reservoirs in China. |
