Research On Numerical Well Testing Theory And Application Of Two-Phase Flow For Fractured-Vuggy Carbonate Reservoirs

During the 12 th five year plan period,China achieved a significant breakthrough in the exploration and development technology of ultra deep fractured-vuggy marine carbonate reservoirs.The carbonate reservoir is deeply buried(with a main body greater than 6000m),aged(Lower Paleozoic),and has a complex distribution of oli and gas.After multiple periods of tectonic activity,weathering and erosion,karst superposition,and fault transformation,it exhibits strong heterogeneity.Formed a complex fractured-vuggy reservoir mainly composed of large scale vugs,pores,and fractures,with a variety of fracture and vug medium combination connectivity pattern.The highly dispersed fractures,vug,and pores determine the complexity of fluid flow characteristics in fractured-vuggy reservoirs.The application of conventional media seepage theory to interprete the measured data of fractured-vuggy reservoirs cannot fully reveal the flow patterns,flow types,and coupling modes of fluids in fractured-vuggy reservoirs.Conventional well testing physical models cannot reflect the multi type combination structure of fracture and vug media,therefore,in-depth research is needed from aspects such as fracture and vug structure,fluid flow,numerical well testing model and application.This article is based on the complex combination structure of fractures and vugs in ultra deep fractured-vuggy marine carbonate reservoirs,studying the complex fluid flow patterns in fractured and vuggy medium formed by karst vugs,dissolved pores,and fractures and forming a well testing interpretation method for fractured-vuggy reservoirs.This article takes the research oilfield of Tahe and Shunbei as the background,and determines the geometric description parameters of fractures,vugs,and pores in carbonate reservoirs by analyzing the distribution characteristics of dissolved pores,faults,fractures,and vugs controlled by the development and tectonic action of fault zones in fractured-vuggy reservoirs,as well as the three-dimensional spatial combination structural mode.According to the Monte Carlo randomness simulation method,a statistically significant discrete network model is formed using probability density functions.Considering the vertical,fractured,and horiontal well and their combination with fractures and vugs,establish discrete fracture and discrete vug patterns with radial composite and linear composite reservoir characteristics,respectively.Considering the various elements involved in typical patterns of fractured-vuggy reservoirs,a local mesh refinement method is studied,based on the limited points and line characteristics of different elements in the fractured and vuggy medium.Implemented the generation of unstructured 2D and 3D PEBI grids.Considering the fluid flow mode,gravity,capillary force,partial perforation,coupling relationship between different flow modes,plane and longitudinal heterogeneity in fractured-vuggy reservoirs,a well testing mathematical model of three-dimensional oil-water two-phase flow for fractured-vuggy reservoirs is established.Based on the finite volume method,an implicit numerical discrete model for oil-water two-phase flow was derived.Using the two-point flow approximation(TPFA)theory,the calculation method for the conductivity coefficient between different attribute grids was determined.This article provides a solution method for large sparse nonlinear matrices and enriches the numerical well testing theory of oil-water two-phase flow in fractured-vuggy reservoirs.Based on the established typical fracture-vug patterns and unstructured PEBI mesh generation method,considering the problems of discrete fractures,discrete vugs,and partial perforation encountered by different well types during drilling,typical curves of oil-water two-phase flow well testing were drawn and analyzed for typical patterns.Divided the fluid flow stages of typical well testing curves.Sensitivity analysis was conducted considering the effects of parameters such as oil-water viscosity,permeability curve,vug radius,reservoir distribution layers,and initial water saturation on the well testing curves.Explained the impact of main parameters on well testing curves and revealed the pressure variation characteristics and fluid flow patterns of typical modes.Based on the numerical well testing theory of oil-water two-phase flow studied in this article,and the analysis of the characteristics of curves,combined with dynamic and static data,such as measured well testing curves,logging interpretation,production performance,seismic reflection,etc.,the measured well testing data were interpreted.The article provides well test interpretation results for four of the actual wells.The interpretation results of the measured well test data indicate that the numerical well test theory of oil-water two-phase flow in fractured-vuggy reservoirs formed in this paper is more suitable for interpreting the measured data of Tahe and Shunbei oilfields.Be able to determine the corresponding relationship between the single well testing curve and the type of fractured-vuggy reservoir,and obtain the characteristic parameters,including vug volume,large fracture length,discrete fractures length,regional permeability,and other parameters.This article studies the numerical theory of two-phase flow in fractured-vuggy reservoirs,forming a set of oil water two-phase flow numerical well testing analysis methods suitable,providing a scientific basis for the analysis and application of measured well testing data in fractured-vuggy reservoirs.