| Horizontal well technology is an efficient oilfield developing and potential tapping technology,which enhances oil recovery and has been widely used in oil and gas exploration and development inrecent years. During injection and production processes, wellbore and reservoir influence and restricteach other, constituting a complex wellbore-reservoir coupling dynamical system. Theoretical andexperimental studies on wellbore-reservoir coupling for horizontal wells are significant for therecognition of coupling mechanism and the prediction of injection/production performances. Theresults can also guide the optimization of injection/production programs and improve the developmenteffect of horizontal wells.In this paper, the main works are as follows:1. Considering the flow characteristics and coupling mechanism of wellbore and reservoir, acomprehensive wellbore-reservoir coupling model is developed by using continuum mechanicsapproach, based on the theories of solid mechanics, fluid mechanics, seepage mechanics and heattransfer. In this model, the free flow in wellbore is described by Navier-Stokes equation (NS), and theporous media flow in reservoir is described by Darcy Law (DL). Not only the coupling of wellboreflow and reservoir flow, but also the coupling of fluid flow, heat transfer and rock deformation, aretaken into account in this model, which provides a theoretical basis for the dynamic characteristicstudy of wellbore-reservoir system.2. By using Brinkman equation (BR) to describe the near-well transitional flow between the freeflow in wellbore and the porous media flow in reservoir, a NS-BR-DL-based approach to couplewellbore flow and reservoir flow is established, which provides a new way for more accuratedescription of the coupling process and further study of the coupling mechanism. In addition, theNavies-Stokes and Brinkman equations discretized by Galerkin/least-squares finite element method,along with the Darcy Equation discretized by standard Galerkin finite element method are solvedsimultaneously. On the basis of previous research, an improved equivalent permeability model andmethod is developed, considering the influence of radial inflow/outflow on the pressure loss along thewellbore under different flow patterns. The results can provide an effective way for the oilfield-level,large-scale numerical simulation of coupled wellbore flow and reservoir flow.3. Based on the improved equivalent permeability method, an iterative solution method isestablished for double coupled wellbore-reservoir problems under the thermal-hydro-mechanicalcoupling conditions. This method uses standard Galerkin finite element method for spatial discretization and second order backward difference method for temporal discretization. The thermalconvection diffusion equation is solved by using stabilized artificial viscosity method, which avoidsspurious oscillations of standard Galerkin finite element method under convection dominatedconditions. Considering the wellbore-reservoir system in both steam injection and oil productionprocesses, temporal/spatial variations and dynamic coupling relationships of temperature, pressure,stress, porosity and permeability characteristics are analyzed quantitatively.4. Based on the idea of source function and the principle of potential superposition, asemi-analytical method for wellbore-reservoir coupling problems is developed for horizontal wells inhomogeneous isotropic reservoirs under weak hydro-mechanical coupling conditions. Extended by aseries of measures, such as coordinate transformation and heterogeneity quantitative characterization,this method can also apply to highly deviated wells and heterogeneous, anisotropic reservoirs,providing an effective way for quick prediction of injection/production performances of horizontalwells.. The effects of deviation angle, heterogeneity and anisotropy on the inflow performance andflow/pressure profiles of horizontal wells are studied quantitatively.5. Based on the principle of potential superposition, empirical skin factor method for quantitativecharacterization of perforation convergence and near-well formation damage is combined with sourcefunction method for the semi-analytical solution of wellbore-reservoir coupling problems ofperforated horizontal wells. On this basis, a new method for adjusting production profiles ofhorizontal wells in heterogeneous reservoirs through variable-depth and variable-density perforatingis proposed, which provides a theoretical basis for the design of perforating program of horizontalwells. The effects of casing size and near-well heterogeneity on variable-parameter perforating areanalyzed quantitatively.6. Based on the theory of flow similarity, ground small-scale model tests of perforatedhorizontal-well wellbore-reservoir coupling are carried out. Comparing flow data of perforatedsegments under different perforating programs, the effect of adjusting production profiles of thevariable-parameter perforating method is verified and some related recommendations for applicationare given. On this basis, a perforation optimization software for horizontal wells is developed inVisual Basic, by which the perforation programs of10horizontal wells in oil field are optimized.Through comparison of production data before and after optimization, the effects of thevariable-parameter perforating method are further examined. |
