Study On Gas Reservoir Underground Gas Storage Fractured Reservoir Stability Assessment

Natural gas is an important non-renewable energy source,with clean and environmentally friendly characteristics.Under the guidance of Chinese sustainable development concept,the status of natural gas in the energy system is rising.In order to ensure a healthy and stable energy environment in China and reduce the occurrence of gas shortage,it is necessary to build Underground Gas Storage reservoirs for natural gas reserves.Depleted oil and gas reservoirs are the most numerous and longest-lived type of gas reservoirs in the world at present.The gas injection and extraction behavior will affect the rock strength of fractured reservoirs during the operation process,which in turn affects the safety and stability of gas reservoirs,so it is necessary to ensure the stable operation of fractured reservoirs in gas reservoirs.In this paper,based on the comprehensive research method of theoretical analysis and numerical simulation,the factors influencing the stability of fractured reservoirs in gas reservoirs are discussed,and a comprehensive assessment model of the stability of fractured reservoirs in gas reservoirs is established.The model is validated by example application and Grey Relation Analysis.Firstly,based on the study of the operational characteristics of gas reservoirs,a large amount of literature was reviewed,and the causes of fractured reservoir instability in gas reservoirs were summarized by combining experimental data and example statistics,identifying the key factors affecting the stability of fractured reservoirs in gas reservoirs.Numerical analysis was conducted by finite element software to explore the influence law of each factor on the stability of fractured reservoirs in gas reservoirs.Secondly,based on the assessment guidelines of gas reservoir fracture reservoir stability and the numerical simulation calculation results of key factors,a gas reservoir fracture reservoir stability assessment index system is established based on the geomechanical characteristics of fracture reservoir,structural characteristics of gas reservoir fracture reservoir and injection and extraction working conditions.In order to assess the stability of fractured reservoirs more accurately,the correlation coefficients among the indicators were derived through correlation analysis and applied to the Entropy Weight Method to determine the final weights of the indicators and the composite index.The stability status of fractured reservoirs in gas reservoirs is divided into five classes,and the Fuzzy C-Means cluster analysis(FCM)method is applied to establish a comprehensive evaluation model for the stability of fractured reservoirs in gas reservoirs.Finally,the stability assessment model is applied to the H Underground Gas Storage as an example,and the Grey Relation Analysis is used to compare,analyze and validate with the model constructed in this paper.The result shows that the stability assessment results of the fractured reservoir in gas reservoir H by applying the model of this paper and the Grey Relation Analysis are bothⅡ stable,which verifies the effectiveness of the model of this paper in assessing the stability of the fractured reservoir in gas reservoir.Compared with the Grey Relation Analysis,the comprehensive evaluation model proposed in this paper has more accurate calculation results.Compared with the Grey Relation Analysis method,the comprehensive assessment model proposed in this paper has more accurate calculation results.Therefore,the fractured reservoir stability assessment model proposed in this paper is reasonable and operable,and it can provide theoretical support for the system safety management of fractured reservoirs during the operation period of gas reservoirs and serve the safe production of natural gas in gas reservoirs.