Research On Seepage Mechanism And Gas Flooding Cooperative Development Method Of Gas Stroage Converted From Gas Cap Reservoir

The development of undeground gas storage(UGS)converted from oil reservoir is of great significance to rapidly improve peak regulation capacity and ensure energy security.Compared with gas storage converted from gas reservoir,the law of seepage and phase behavoir change during multi-cycle injection and production in gas storage converted from gas cap reservoir is more complicated,which greatly increases the difficulty of evaluation of storage capacity index.Meanwhile,the key to realize the integrated construction is to enhance the recovery efficiency in the process of gas storage construction.Aiming at the above problems,this paper focuses on the study of multicycle injection production seepage mechanism,gas storage capacity calculation and collaborative development method in gas storage converted from gas cap reservoir through the combination of laboratory experiments,theoretical derivation and numerical simulation,and the combination of qualitative and quantitative methods.In view of the problem of seapage variation in porous media under cyclic alternating operating pressure of gas storage in gas cap reservoir,firstly,the effects of variation of stress path on the rock stress sensitivity of gas storage during multi-cycle injection and production are revealed through physical simulation experiments.Based on the experimental results,the stress sensitive hysteresis characterization model of gas storage is established.Secondly,the effect of the variation of saturated path on the seepage capacity of gas-liquid system in the multi-cycle injection and production was revealed through the multi-cycle mutual flooding experiment,and relative permeability hysteresis models were introduced to evaluate the adaptability of the relative permeability change low of multi-cycle injection and production process.Finally,in view of the defects of Larsen model in the characterization of non-wetting phase periodic hysteresis effect,the quantitative characterization of multi-cycle injection and production relative permeability hysteresis effect was realized by modified Land trap model and Larsen hysteresis model.On this basis,a numerical simulation model of gas storage considering stress sensitive hysteresis and relative permeability hysteresis is constructed,and the dynamic characteristics of multi-cycle operation of gas storage under the influence of stress sensitive hysteresis and relative permeability hysteresis are further studied.In order to evaluate the storage capacity of gas storage converted from gas-cap reservoir with the influence of water intrusion,firstly,a water influx calculation model during multi-cycle injection and production is derived,which takes into account the change of gas reverse condensate,secondary dissolution of natural gas and deformation of rock and bound water.Secondly,through the fine division of gas storage area under gas invasion and oil invasion conditions,the effective pore volume was introduced to characterize the available pore space in each zone of the gas storage.Considering the effect of edge and bottom water intrusion,gas-liquid alternate displacement and rock and bound water deformation on effective pore volume,a multi-period injection and production reservoir capacity evaluation method is established.Finally,based on this model,the influencing factors and control ideas of gas storage converted from gas cap reservoir are studied.Aiming at the synergistic problem of EOR by gas flooding,and discharge of liquid and expand of capacity in gas storage converted from gas cap reservoir,a multi-stage collaborative development method is proposed.According to the EOR mechanism of natural gas flooding and the operation characteristics of gas storage,the full-cycle cooperative development stage of gas storage is divided,the evaluation index system of multi-stage cooperative development is determined,the technical policy limit and feasibility evaluation of multi-stage cooperative development are carried out,and a set of cooperative development mechanism in gas storage converted from gas cap reservoir is formed.The multi-stage collaborative development scheme of S67-2 gas cap reservoir is designed by using the multi-stage collaborative development method.The numerical simulation results show that the multi-stage collaborative development method can effectively improve the oil recovery,expand the storage space,optimize the storage capacity structure and improve the operating efficiency of the gas storage.This paper develops the seepage theory and storage capacity parameter evaluation method in gas storage coverted from gas cap reservoir,and the proposed multi-stage collaborative development method realizes the technical coupling of gas flooding and gas storage construction.The research results have important theoretical significance and reference value for improving the technical theory of gas storage converted from gas cap reservoir and implementing gas flooding collaborative integrated gas storage construction.