Three-dimensional Fine Hydrogeological Model Of Underground Water-sealed Oil Storage Caverns:Method And Application

Large underground water-sealed oil storage caverns have become the main form of storage for China’s national energy strategic petroleum reserve by virtue of their advantages of small land area,large reserve capacity,high safety and short construction period.Water seal effect evaluation of underground oil storage caverns needs to be based on the hydrogeological phenomena and related basic data information on site.However,since most of the hydrogeological phenomena are hidden deep underground,and the distribution of exploration works is uneven and limited,it directly affects the accuracy and reliability of water seal effect evaluation.Using the hydrogeological data obtained from the actual survey to establish a three-dimensional fine hydrogeological model that can fully respond to the evolution of the groundwater seepage field can reflect the hydrogeological situation of the storage caverns area intuitively,accurately and completely.Therefore,how to use different sources of situ exploration and monitoring data,through the analysis of hydrological geological knowledge integrating data processing with the actual situation,to build a suitable for large underground water seal oil depot engineering three-dimensional fine hydrogeological model,and refer to the in-depth study and model reveal space-time evolution characteristics of underground water seal oil depot of groundwater seepage field,has the very vital significance.This paper takes the field of three-dimensional hydrogeological modelling as the research background,and carries out research on the key work of water seal effect evaluation of underground water-sealed oil storage caverns and the three-dimensional fine hydrogeological modelling and calibration method of underground water-sealed oil storage caverns.This paper also research on the analysis of the spatial and temporal evolution law of seepage field,and carries out feedback analysis on the relevant parameters of water sealability evaluation,and achieves the following results.(1)A method is proposed for the establishment of a three-dimensional fine hydrogeological model of underground water-sealed oil storage caverns.This method scientifically selects large independent hydrogeological units within the storage site area,and proposes the comprehensive use of borehole,physical prospecting,construction exploration and other data to establish a three-dimensional hydrogeological fine dynamic geometric model.Based on hydraulic pressure tests,water curtain system tests,water inflow monitoring and other data information analysis,determine the accurate physical parameters of the hydrogeological model.Based on the engineering background of a large underground water-sealed oil storage caverns in south China,a three-dimensional fine hydrogeological model of the large underground water-sealed oil storage caverns was constructed through field investigation,data collection and pretreatment,geometric and physical modelling and other steps.(2)A method was developed to calibrate the initial conditions,boundary conditions and other hydrogeological parameters of the three-dimensional fine hydrogeological model based on exploration data and construction phase information.The method uses field research,theoretical analysis and numerical simulation to calibrate the constructed three-dimensional fine hydrogeological model.It also relies on a large underground water-sealed oil storage caverns project in China,conducts on-site research on the groundwater seepage field in the storage caverns site area,uses numerical simulation software based on finite element theory to simulate the evolution of the seepage field,simulates the spatial and temporal evolution of the seepage field in the excavation process of the underground water-sealed oil storage caverns,and uses forward and backward analysis,combines with engineering monitoring data to correct the seepage parameters,optimises and calibrates the three-dimensional hydrogeological physical model,selects a typical section of the model The model is used to determine the changes in pressure distribution and groundwater flow rate during the construction process.(3)The constructed and calibrated three-dimensional fine hydrogeological model is applied in engineering.A large underground water-sealed oil storage caverns is simulated and analysed to predict the water level and cavern surge during the operation period of the large underground water-sealed oil storage caverns.Based on the simulation results of the evolution of the seepage field during the operation period,the relevant parameters of the numerical model are modified to determine the hydraulic connection of the hydrogeological units of the model through feedback analysis of the geometrical and physical parameters of the model by modifying the relevant parameters of the numerical model with respect to the natural and engineering conditions such as rainfall infiltration and geological formations,the water sealability of the water curtain system,the effect of grouting and seepage reduction,and the burial depth of the underground facilities in the study area,respectively.The actual impact of the existing excavation process,grouting process and water curtain system on the evolution of the complex seepage field in the storage caverns site area is analysed.(4)A discussion of a number of issues based on the construction of a three-dimensional fine hydrogeological model of a subsurface water-sealed oil storage caverns is carried out.Firstly,the general process and requirements of water sealability evaluation based on the three-dimensional fine hydrogeological model are proposed.A technical audit of the water sealability evaluation of underground water-sealed storage caverns is proposed.The technical audit focuses on the water sealability evaluation objectives,concepts,numerical analysis techniques and their accuracy,and other issues that should be the focus of water sealability evaluation,and specifies the requirements that need to be met in the water sealability evaluation process.Finally,the problems encountered in the construction and application of the three-dimensional hydrogeological model of underground water-sealed oil storage caverns are discussed,and the problems that should be focused on in the survey,design and construction of the actual project on site are discussed respectively,which are of guiding significance for the same type of underground water-sealed oil storage cavern projects.