Study Of Seal Properties In Underground Oil Storage Cavern Influnced By Rock Cracks

China possesses a large territory and wide distribution of intrusive rock,the rock mass for underground oil cavern construction spreads all over the country.With good engineering and hydrogeological conditions,the eastern coastal regions provide favorable sites for the development of underground oil cavern.A successful underground oil cavern requires good hydrogeological conditions and steady underground water level to prevent the leakage of oil,in the situation of which the cracks are filled with undergroud water.This paper is sponsored by the National Science Foundation Project “Underground oil cavern hydro-mechanical coupling of fractured rock mass characteristics and seal conditions”(Gant No.40902086).Huizhou underground oil cavern,as parts of national oil reserve system,has been detailly studied by the author.Based on engineering geological surveys and water curtain drill image data,the characteristics of the development of joints and cracks in underground rock mass is analyzed,and the crack-pore double medium fluid flow network model is established.Seepage numerical experiments considering borehole pressure under single fracture conditions and seepage stimulations of cavern excavation in surrounding rock mass with complex fractures have been conducted with the aid of finite element method(Comsol).The research work mainly focuses on:(1)Classification of underground water and its distribution in the studied area are identified through hydro-geological survey and hydro-geological experiments of drills,the vertical variation of permeability in rock mass with fractures is also analyzed.Attitudes of structure planes in surface,tunnels of water curtain and main cavern are measured and analyzed,the collection and calculation of structure planes are performed based on water curtain drill image data.Through these data,distribution of joints and cracks in the studied area is analyzed and regional fracture network model is established.(2)Under the situation of water curtain drilling pressure,numerical experiments are conducted to assess the impact on seepage in drills with and without cracks based on the cubic law.It provides a theoretical basis for the simulation of seepage in surrounding rock mass with complex fractures of the underground water-sealed oil cavern.(3)Three-dimensional geometric model of Huizhou water-sealed oil cavern is established via Comsol software.Varations of pore water pressure in two typical profiles with two sets of dominate fractures is stimulated during the excavation of main cavern groups.Comparison is also made between the results under the condition of cracks in the rock mass and nonexistence of the cracks.(4)During the stratified excavation of main caverns,comparison between the variation of seepage in crack rock mass with water curtains and without water curtains are made,combined with the simulation of seepage under the condition of grouting cracks in surrounding rock mass of the main cave,the effect of water seal and configuration of water curtain is assessed and seepage volume of caverns is predicted.