Study On Multiphase Flow Mechanism Of Deep Condensate Gas Reservoirs

Condensate gas reservoirs are widely distributed in China,but most of them are buried deep underground.Currently,deep condensate gas resources account for more than 60%of the total condensate gas reserves.Deep condensate gas reservoirs feature various storage spaces,strong heterogeneity,and high in-situ stress environment,making the distribution of gas-oil-water and the law of multiphase movement more complicated.In the development process of deep condensate gas reserves,the oil-gas-water multiphase interflow occurs,and the multiphase seepage law and mechanism are not clear.Besides,the injected gas overburden takes place in the gas injection development,which hinders the efficient development of deep condensate gas reservoirs.Sponsored by the CNPC's major scientific and technological project "Research on key technologies for improving development effects of deep/ultra-deep condensate gas reservoirs" and aiming at the multiphase seepage problems as gas-oil-water co-flowing behavior and injected gas override in the development process,and considering the influence of high stress sensitivity and solid deposition on multiphase flow,this thesis makes a systematic study combined with theory and numerical simulation methods on the basis of experiments.(1)Using core slices and micro-etching techniques,microscopic models of different pore types and scales were made.Afterwards,microscopic visual seepage experiments were carried out to clarify the flowing patterns of gas-oil-water at different saturations in the development of condensate reservoirs.Furthermore,the formation mechanism of multiple micro-interface phenomena was illustrated with numerical simulation methods.In the end,a relative permeability calculation method at micro-scale was created to realize the organic combination of microseepage characteristics and seepage laws.(2)An experimental device and corresponding testing method are developed for gas overburden phenomenon.Aiming at the commonly used injector-producer patterns,the overriding and migration mechanism of injected gas was studied.Further theoretical study discussed the non-equilibrium stable characteristics of injected gas/condensate gas system at later stage of gas overriding with nonequilibrium thermodynamics.In the end,the application effects of different injection-production combinations in real reservoirs were studied with numerical techniques.(3)Aiming at the high ground stress in deep formations,cores with common matrix,fractures,and caverns were selected to study stress sensitivity of different cores in deep formations.The tests recognized stress sensitivity laws of different cores and clarified the stress sensitivity limits.In the end,the effects of stress sensitivity on production and formation properties were investigated by numerical simulations.(4)On the basis of experiments,a mathematical model considering injected gas was established to describe the multi-phase seepage behavior in deep formations,which comprises:An equivalent permeability model to describe double porosity system;a phase equilibrium mathematical model to characterize phase change behavior of deep reservoir fluids;a solid deposition model to describe the solid deposition problems in the reservoir.Finally,numerical simulation analysis was carried out on a typical block to explore the influence of stress-sensitive and solid deposition on the flowing behavior of deep fluids.This research focuses on solving the several core problems in the development of deep gas reservoirs.Relevant experimental devices and methods have been developed and formulated to deepen the understanding of the multiphase flow behavior of deep fluids,which can effectively guide the efficient development of deep condensate gas reservoirs.