| As a clean energy with good economy and environmental protection,natural gas has been widely used in civil field and many industrial development.According to the energy structure and the imbalance of natural gas consumption,the contradiction between natural gas supply and peak adjustment is caused.Generally speaking,the average demand of natural gas in winter is 1.5-2 times of the average demand in summer,and even 10 times in big cities such as Beijing.If calculated according to the maximum daily demand,the demand in winter can reach 10-15 times of the demand in summer.According to the analysis of the demand and consumption structure of natural gas in domestic market,the provinces with the largest demand are Beijing,Tianjin,Shandong,Hebei and Jiangsu in turn.With the steady and rapid development of economy,the demand for natural gas is also growing continuously,and accelerating the construction of underground gas storage is also increasingly urgent.At present,the existing depleted gas reservoir can not meet the demand,and the remaining reservoirs need to be screened in later stages.Aquifer gas reservoir is the second type of underground gas storage,which has accounted for 16.8% of the total number of underground gas reservoirs.Under the condition of limited traps of suitable depleted gas reservoirs,it is an important development direction to find aquifer traps and reconstruct gas reservoirs.X oilfield is located in Bohai rim area,rich in closed water resources,and has been developing oil and gas exploration and development for more than 50 years,accumulating a large number of 3D seismic and drilling data.It has the advantages of location and technology to build aquifer gas reservoir around Bohai Sea and Shandong.Since 2002,X oilfield has evaluated the geological structure of depleted oil and gas reservoir and underground water bearing circle in the block of mineral right for many times,and preliminarily screened the resources suitable for the construction of underground gas storage.Whether the sealing of the cap and fault can form effective traps for the injected gas is the key and difficult point in the reservoir construction.Unlike the depleted gas reservoir,the sealing property and fault sealing property of gas reservoir traps are known,and the upper pressure coefficient is less than 1.0,while the upper pressure coefficient of aquifer gas reservoir can reach 1.7.The trap of gas storage must undergo multi cycle strong injection and cycle,and the change of the stress cycle disturbance of traps and fault layers is large,which will lead to the fracture of the cap or the opening of faults.Therefore,the combination of theoretical analysis and numerical analysis is used to provide scientific and reasonable technical support for the sealing evaluation and mechanical stability analysis of the trap fault in the reconstruction of gas reservoir by using rock mechanics test,seismic logging data,field geological exploration data,and finite element software.The research ideas of this paper are summarized as follows:1.Aiming at the problems of low degree of water bearing circle closed exploration and less data,a static sealing index system of fault with "fault rock lithology,fault mechanics,sealing fault environment condition and fault occurrence" as the core is constructed.Combined with MATLAB software,the static sealing evaluation system of aquifer closed fault is established by using the method of chromatography analysis,and the evaluation system is applied to the reconstruction of X oilfield In the aquifer gas reservoir,the analysis results show that the target fault has strong sealing ability and certain sealing capacity,but proper monitoring wells must be deployed in the reservoir outside the fault.The sealing performance of the fault is evaluated dynamically by monitoring the pressure change of the peripheral reservoir and the change of gas water interface.The technology of static sealing evaluation of aquifer trap fault in complex geological conditions is enriched and perfected by combining directly with indirect.2.Based on the existing experimental experience,the evolution law of fracture permeability and stress sensitivity analysis under the condition of multi cycle alternating stress are analyzed.The mathematical model of dynamic sealing evaluation of fault is established.The model is applied to the dynamic sealing evaluation of gas storage during the alternation injection and production process.The influence of the evolution of permeability on the dynamic sealing of fault is discussed The results show that the understanding of fault and dynamic sealing of gas storage is improved,and the reference for safe operation of gas storage is provided.3.Based on the theory of seepage stress coupling,a large-scale finite element twodimensional geomechanical model is established.The stress sensitivity of multi factor fault under complex geological conditions is studied.The dynamic sealing and mechanical stability of faults under the condition of multi cycle alternate injection and production are analyzed by using analytical and numerical methods.The results show that the numerical method and analytical method can be applied to fault fault very well The failure mechanism of the layer is studied,and the stress,the dip angle of the fault and the normal / reverse fault are discussed The sensitivity of faults under the injection/ downinjection production mode is evaluated by morcoulon criterion,shear slip critical value and CFF evaluation criterion.It provides reliable and scientific basis for the operation,monitoring and safety prediction of gas storage under multi cycle injection and production conditions.4.Based on the above research model,the finite element geomechanical model of aquifer trap in X oilfield is established based on the closed structure of water bearing circle in X oilfield.According to the injection production pressure curve calculated by reservoir numerical simulation software,the mechanical stability of fault under multi cycle injection and production conditions is analyzed.The results show that the reservoir location is the first shear slip failure in the multi cycle injection production process Fault;25 months after injection and production,the faults at reservoir,cap and upper aquifer respectively produced 1.391 mm,0.154 mm and 0.878 mm slip.Combined with morkulen criterion,the fault produced by reservoir has shear failure,but no hydraulic fracturing failure occurs.Therefore,the target fault is in a safe and stable state. |
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