Possible Continuous Vertical Water Leakage of Deep Aquifer: Records from a Deep Well in Tianjin Province, North China

Abstract

It is well known that the storage of the valuable helium and other natural gases needs thick well-confined aquitards. Meanwhile, the assumption that deep aquifers are confined is most evident from the wide practices of targeting deep aquifers as the storage of toxic wastes and CO2. With the negative phase shifts of the M2 tidal wave, previously, deep Gaocun well (~3500 m) in the North China Platform is assumed to be confined fairly well. However, water level of the Gaocun well has been continuously decreasing for ~40 years without coseismic variations and without explainable mechanism. In this study, innovatively, we find that even buried in ~3500 meters deep, and covered by thick compact mudstones, the aquifer of well Gaocun is calculated to be continuously leaking for ~40 years probably induced by the vertical leakage incurred by aquitard fractures, which is under the assumptions of the none-leaking bottom layer and none direct pumping or exploiting in the observation aquifer layer. Meanwhile, for the first time, we did a detailed systematic comparison between the leaky models of the tidal response and the barometric response of water level, which indicate a consistency leaky result, and the minor difference mainly induced by the frequency differences. Merits and demerits of both models are also analyzed. Last but not least, underground fluid leakages might frequently occur, which are becoming increasingly worldwide urgent since that might also be related with surface sourced contaminations, toxic waste burials, and burial and exploration of the natural gas reservoirs.

Comprehensive quantitative determination of aquifer confinement based on tidal response of well water level and its application in North China

“…S1 ) 16 , 23 , 33 , 34 , it has been observed that in confined aquifers, the phase shift is negative, whereas when in the unconfined aquifer, the phase shift is positive. Thus, the phase shift of the M 2 wave can be used to determine aquifer confinement 9 , 22 .…”

“…Several quantitative methods have recently been proposed for determining aquifer confinement based on the tidal response of well water level (named “well tide”) 2 , 9 , 18 , 20 – 22 . An increasing number of studies are using tidal methods to investigate the effects of human activities and earthquakes on aquifer confinement 23 , 24 .…”

Using the Tidal Response of Groundwater to Assess and Monitor Caprock Confinement in CO2 Geological Sequestration

“…Hence, evaluations based on groundwater age, frequently nearing the 14 C dating threshold, require additional validation. Cosmogenic isotopes, such as 36 Cl (half-life: 301 ka), though useful for older water, present challenges due to subsurface production [70]; similarly, cosmogenic 81 Kr (half-life: 229 ka) is viable provided issues related to air contamination are addressed [71]. The utilization of multiple tracers is generally advantageous [72].…”

Using the Periodic Dynamics of Well Water Levels to Estimate Time Series Changes in Aquifer Parameters

“…Sun et al [31] calculated the aquifer parameters using a graphical method, where only one set of T and σ values can be obtained at a time. Yang et al [30,32,33] used tide M 2 and O 1 responses in a least squares inversion of the unknown parameters in the leaky aquifer model, with three inputs used to obtain three parameters (S, T, and σ) simultaneously, which reflect the water storage capacity and the horizontal and vertical water exchange capacity of the aquifer. This method is suitable for situations where the phase shift of tide O 1 is greater than that of tide M 2 .…”