| Underground water-sealed cavern is the best form of oil storage,which has been developed vigorously in China by virtue of its advantages such as small occupation,high security,large reserve and environmental protection.In order to ensure the stability and water sealing requirements of underground water-sealed caverns,the site of the caverns should be selected in the coastal area with good regional stability,good rock quality and stable groundwater.Due to the excavation of underground water-sealed caverns,the initial groundwater level drops greatly,and the balance between fresh water and seawater is destroyed,resulting in seawater intrusion.Seawater intrusion into underground water-sealed caverns will corrode the facilities and surrounding rocks of the caverns,which will affect the service life of underground water-sealed oil caverns.Seawater and surrounding rock will also have a chemical reaction,resulting in oil pollution products,affecting the quality of oil.Therefore,attention should be paid to seawater intrusion in the construction of underground water-sealed oil caverns in coastal areas,so as to avoid unnecessary losses.The research on seawater intrusion mechanism and control method of underground water-sealed oil caverns in this paper has important security significance and scientific value.In this study,seawater intrusion evaluation and control methods were studied based on an underground water-sealed cavern project.Using the finite element numerical simulation method,a three-dimensional numerical model of underground water-sealed caverns based on the convection-diffusion mechanism was established,and the isotropy and anisotropy of surrounding rock were studied in the absence of water curtain,horizontal water curtain,and horizontal double vertical water curtains.The three conditions affect the seepage field and solute transport characteristics of the reservoir area,and the method of seawater intrusion control of underground water-sealed caverns is proposed.The main research contents are as follows:Based on the site survey data of the reservoir site,a three-dimensional numerical model of the study area under isotropic surrounding rock conditions is established.Based on the principle of seawater intrusion control,the two physical fields of seepage field and transport field are coupled to simulate and analyze.Only a horizontal water curtain system cannot prevent seawater intrusion.A vertical water curtain system must be added to completely suppress seawater intrusion.Under the premise of suppressing seawater intrusion,the water level of the reservoir area can meet the water seal of the cavern.Requirements,but the amount of water inflow has increased.Based on the fracture parameters obtained in the field,the dominant fracture occurrence is calculated,and the main value of the permeability tensor and the direction of permeability are calculated to reflect the anisotropic characteristics of the permeability of the fractured rock mass medium.The two conditions of isotropy and anisotropy are compared and analyzed,and the vertical water curtain system with the same isotropic conditions is set.The vertical axis of the cave cannot achieve the purpose of completely preventing the intrusion of seawater into the cave,and the vertical must be deepened.The bottom of the water curtain hole exceeds the depth of the bottom plate to achieve the goal.With the change of the permeation principal value anisotropy ratio,the concentration difference in different directions of the cavern increases.The anisotropy ratio of the fractured rock mass affects the distribution of groundwater pore water pressure,seepage velocity and water inflow,among which the influence on the caverns on both sides is relatively large,and the influence on the middle cavern is relatively small.Combined with the anisotropy of fracture seepage,consider the hydrodynamic dispersion coefficient.After adding the influence of fissures on the hydrodynamic dispersion coefficient,the greater the dispersion,the better the effect of the horizontal and vertical double water curtains in preventing seawater intrusion.The degree of influence of diffusion coefficient,horizontal dispersion and longitudinal dispersion on the characteristics of seawater intrusion in underground water-sealed caverns increases in turn.Affected by the different directions of surrounding rock permeability,the hydrodynamic dispersion coefficient has different influences on all directions of the cavern.The change of longitudinal dispersion and lateral dispersion has almost no effect on the groundwater level and water inflow. |
