关键词: 流体观测井, 微水试验, 井-含水层系统, 导水系数, 同震响应

Abstract:

Hydraulic parameters of aquifers are important parameters for studying the rule of groundwater movement, and also key parameters for regional groundwater resource evaluation, groundwater flow numerical simulation and groundwater quantitative calculation. Aquifer hydraulic parameters also play an important role in the study of groundwater dynamic characteristics and their relationship with earthquakes. Among all kinds of hydrological responses caused by earthquakes, the change in well water level is the most common. Stress accumulation in the process of earthquake preparation, static stress caused by fault dislocation after the earthquake, and dynamic stress caused by seismic wave propagation will lead to the change of crust-media structure at local or regional scales, which will inevitably lead to the change of media characteristics(such as permeability)of the aquifer in the rock mass. As a result, the well water level will change. Therefore, the study of aquifer hydraulic parameters is of great significance to understand the role of groundwater in the process of earthquake preparation and occurrence to understand the hydrological response mechanism related to earthquakes.
China has the largest seismic underground fluid observation network in the world, but most of the observation wells are transformed from geological and petroleum wells, lack complete basic data, and most of the hydraulic parameters of the aquifer are unknown. For underground water level real-time monitoring wells or seismic precursor information observation wells, hydraulic parameters can be obtained by traditional pumping test methods when the well is completed, but it is difficult to implement in order to ensure the continuity of observation data after the well is put into use. The hydraulic parameters of the-well-aquifer system often change with the change in the regional groundwater environment. In order to more accurately interpret the dynamic changes of the observed well water level, we need to obtain the hydraulic parameters of the-well-aquifer system under the current state. As a single well hydraulic test, the slug test has the characteristics of convenient operation, short test time, and low disturbance to aquifer, which can easily and relatively quickly obtain the hydraulic parameters of well-aquifer. With the advent of the digital water level measuring instrument of second sampling rate and its widespread use in the observation of underground fluid, the slug test method is more widely used in the determination of hydraulic parameters of the underground fluid aquifer.
In this paper, the water-level time response data of 8 wells in Shanxi area were obtained by using the Slug test method, and the water conductance coefficient of the observed aquifer was estimated by selecting the corresponding data analysis model according to the attenuation type of water level. The coefficient of transmissivity of each well-aquifer is compared and analyzed by statistics of the co-seismic response of each well and discusses the reliability of the Slug test estimation results and the applicability of the method. The following conclusions are obtained: 1)The co-seismic response of wells with large transmissivity is usually of vibration type. 2)The hydrogeological parameters of the well-aquifer can be obtained dynamically by the Slug test, and the subtle changes of aquifer medium state can be captured to interpret the dynamic changes of well water level more accurately. 3)With the popularization of water level high-frequency sampling observation instruments, the Slug test has been well used in the parameter determination of high permeability medium in underground fluids.
The results show that the slug test method can quickly and accurately obtain the hydraulic parameters of the well-aquifer, capture the change of aquifer medium state in time, interpret the dynamic change of well water level more accurately, and conduct quantitative analysis of the abnormal change of water level.

Key words: fluid observation wells, Slug test, well-aquifer system, coefficient of transmissivity, co-seismic response