| As a kind of environmental clean energy with good economy,natural gas has been widely used in the civil field and many industrial development.The imbalance of natural gas production mode and consumption in different seasons leads to the contradiction between natural gas supply and peak regulation.Based on the maximum daily demand,winter demand can be 10 to 15 times higher than summer demand.With the stable and rapid development of economy,the domestic demand for natural gas continues to grow,so it is increasingly urgent to accelerate the construction of underground gas storage and enhance the peak regulating capacity of gas storage.S gas storage has accumulated a large number of 3D seismic and drilling data from its construction to its exploitation.The gas reservoir has a good trap environment,strong peaking capacity and high economic application value.Gas storage traps need to undergo multi-cycle intense injection and production,and frequent stress field disturbances may lead to cap fracture or fault activation.Therefore,whether the stability of the trap system during gas injection and cyclic injection and production can effectively seal the storage medium is the key and difficult point.Therefore,by using rock mechanics test,seismic logging data,field geological exploration data and finite element software,theoretical analysis and numerical analysis are combined to provide scientific and reasonable technical support for sealing evaluation of trap fault and mechanical stability analysis of gas storage reconstructed from aquifer structure.The research ideas of this paper are summarized as follows:1.Based on the geological conditions of sand and mudstone fault in the Q3 section of S gas storage,relevant laboratory tests were carried out to discuss the rule of mudstone friction strength changing with mud content in the working condition area,and to study the mechanical characteristics of friction strength of fault filling medium to improve the accuracy of fault activity evaluation and provide a basis for subsequent research on possible fault activation under different mud content.2.Based on the experimental results of the foundation properties of mudstone cap,a series of triaxial mechanical laboratory tests are carried out to study the influence of cyclic injection and production process of gas storage on the fatigue damage characteristics of mudstone,analyze the deformation damage characteristics of mudstone,and reveal the damage evolution process and mechanical failure mechanism of mudstone under multi-period alternating loads.3.Based on the coupling theory of seepage and stress,a two-dimensional finite element geomechanical model is established to discuss the existence of faults under complex geological conditions and the influence of their existing forms on the actual injection-production conditions.The dynamic sealing and mechanical stability of faults under the multi-period alternating injection-production conditions are analyzed using analytical and numerical methods.The numerical method and analytical method can be well applied to the study of fault failure mechanism.The mechanical stability of the fault and the dynamic sealing property are evaluated by Moerculum failure criterion,which provides a reliable basis for the operation,monitoring and safety prediction of gas storage under the condition of multi-cycle injection and production.4.Based on the study of conceptual model and related laboratory tests,the finite element geomechanical model of X oilfield trap is established on the background of the water-bearing trap structure of X oilfield.According to the injection and production pressure in actual working conditions,the mechanical stability of faults under the condition of multi-period injection and production is analyzed.Under the actual injection-production pressure,the gas plume diffused to the reservoir boundary after 156 hours,and produced 3.907 cm cap uplift and 0.6665 cm underlayer subsidence during the 18 months of gas injection and supercharging.According to the Moerculen failure criterion,the target fault was in a safe and stable state during the whole process of supercharging and cyclic injection-production. |
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