| The newly discovered(ultra)deep carbonate fractured-vuggy reservoirs,such as fault-karst reservoirs,have three major characteristics,including complex burial environment,complex mechanism of interaction,and complex storage space.Faultkarst reservoirs are faced with three major challenges: in-depth understanding,effective production,and efficient development.Thus,the basic theoretical research on this kind of reservoir needs to be carried out urgently,and the related development engineering technology also needs to be broken through.In this paper,based on the disciplines of petrophysics,seepage mechanics,reservoir engineering,and engineering mathematics,the flow mechanisms and water injection development method for fault-karst carbonate reservoirs are studied by means of physical simulation experiments at different scales,mathematical model characterization,reservoir engineering theory analysis,and numerical reservoir simulation.Based on the core models of carbonate fractured-vuggy media with different structure characteristics,the permeability variation features of different types of media under alternating stress conditions were investigated.The variation range and distribution mechanism of effective stress coefficients for permeability of the four typical fractured-vuggy media are analyzed by response surface method.A theoretical analysis model of effective stress coefficient considering the triple medium of pores,fractures and vugs is established.The flow test method for stress sensitivity evaluation is improved and the stress sensitivity differences of different types of fractured-vuggy media under deep conditions are clarified.A complete stress sensitivity evaluation system for carbonate fractured-vuggy media is formed.The influence law of different structure on single-phase fluid flow under deep conditions is analyzed.The single-phase flow characteristics of different carbonate media under variable temperature and stress conditions are analyzed respectively.The oil-water two-phase fluid flow law of carbonate fractured-vuggy media under high temperature and pressure conditions is investigated,and the two-phase flow characteristics of different carbonate media are compared respectively,which fully reveals the single-phase and oil-water two-phase fluid flow law of carbonate fracturedvuggy media under deep high temperature,high pressure,and high stress conditions.Based on the three typical geological traps of fault-karst reservoirs,six typical visualized physical models of fault-karst composite media in the horizontal and vertical directions are designed and fabricated.Through carrying out waterflooding experiments under different well patterns and injection-production modes,the mechanism of water drive in different fault-karst reservoirs is studied,the macroscopic sweep characteristics and the dynamic evolution of displacement are analyzed,and the distribution characteristics of macro residual oil and the main types of local residual oil are summarized.The liquid production performance under different injection-production relationships is compared,and a perfect analysis method for the optimization of well patterns is formed,which comprehensively reveals the influence of the well-fracturevug configuration on the development effect of water drive in fault-karst reservoirs.The study on the main control factors of waterflooding development in fault-karst reservoirs is carried out,focusing on the influence law of the main control factors such as fault-karst type,oil-water viscosity ratio,injection volume and injection rate on development effect.Based on the two-phase flow characteristics in fault-karst reservoirs and the basic reservoir engineering theories,a practical integrated forecast method for well-controlled OOIP,EUR and well production performance is proposed.The reliability and accuracy of the forecast models are verified and favourably applied by example in the development of an actual fault-karst reservoir.Taking SX1-1,a typical fault-karst block in Shunbei oilfield of Tarim Basin,as an example,a fine geological model and a numerical reservoir model are constructed based on the actual geological data.The actual development status of the block is analyzed based on the results of production history matching.The key content of waterflooding development plan such as water injection timing,water injection mode and production process parameters are optimized.The development effect under the optimal scheme is predicted and the optimization technology for water injection development in fault-karst reservoirs is developed. |
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