Study On Characteristics Of Salt Dissolution And Salt Plugging During Fracturing Flowback Of Inter-salt Shale Reservoir

In recent years,shale oil and gas development has become a new growth point of oil and gas resources development in China.Among them,the inter-salt shale reservoir is the high-quality hydrocarbon source layer,the oil content per rock is much higher than other Marine and continental shale systems,and the exploitation value is very high.However,hydraulic fracturing is often used in the exploitation of inter-salt shale reservoir.Affected by upper and lower salt layers and soluble salt in reservoir,dissolution and salt formation occur in wellbore and near wellbore zone during the exploitation process,resulting in poor reservoir stability,which brings great challenges to the effective exploitation of reservoir.Therefore,based on the typical characteristics of salt dissolution,salting out and recrystallization in the fracturing and flowback process of inter-salt shale reservoir,dynamic and static salt dissolution experiments under different conditions were carried out in this thesis to explore the causes of salt dissolution,the main controlling factors and the improvement ability of the reservoir.In addition,based on salt-dissolved rock core and salt-containing fracturing fluid obtained after salt-dissolved,salt-out damage simulation experiments under different conditions were carried out to reveal the formation mechanism of salt plugging,make clear the formation characteristics,main controlling factors and critical conditions of salt plugging,and clarify the damage degree of salt plugging to reservoir.The results show that:(1)The lower the salinity of the injected water,the stronger the salt dissolution of the inter-salt shale.In pure fracturing fluid,dissolution is serious,which will lead to core breakage.(2)The order of influencing factors of salt dissolution is temperature > flow rate > pressure;At 70℃,core permeability increases 67 times.The second is the flow rate.When the flow rate is 0.1m L/min,the core permeability increases by 9 times.Pressure has little effect on salt dissolution;(3)Temperature has the most significant effect on salting out.With the decrease of temperature,the solubility of salt minerals in the flowback fracturing fluid decreases,and gradually precipitates,aggregates,nucleates and grows,and preferentially blocks the large pores and fractures in the reservoir,which significantly increases the seepage resistance of the fluid.When the temperature drops from 70℃ to 20℃,the permeability decreases by 95.38%.The work and understanding carried out in this thesis can provide theoretical basis and technical support for effectively utilizing inter-salt shale reservoir and improving single well production.