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Using Well Water Level To Measure Volumetric Strain Considering The Dissipation Effect

Yuqing Xie, Yonghong Zhao, & Lingsen Meng

Published August 15, 2016, SCEC Contribution #6810, 2016 SCEC Annual Meeting Poster #019

Water-levels in confined well can be used as a strain-meter. Periodic amplitude fluctuations of the water-level generally reflect the strain change induced by Earth’s tide. The measured value of well water-levels can be compared with the theoretical volumetric tidal strain at various locations on earth. The amplitude and phase delay between the tidal strain and water-levels can be used to infer the hydrogeological parameters of water-bearing rock. Traditional method analyzes amplitude and phase delay in separate manners. In this study, a deconvolution method considering both the amplitude and phase delay is explored to remove the response of the well-aquifer system from the volumetric strains. A numerical simulation is conducted to demonstrate the feasibility of this method. We establish an ideal 2D confined aquifer model using poroelastic module in COMSOL Multiphysics 5.1, a finite element software. We calculate the response curve of water-levels under a step and periodical changes of burden. Results show when the response curve is known, the variation of the burden can be obtained by deconvoluting response curve from the well water-levels. Likewise, when the variation of burden is given, the response curve can be also computed by deconvolving the loading curve from the well water-levels. We apply the deconvolution method to analyze the water-levels record of Huili Sichuan-06 well, located at Sichuan Province, southwestern China. The response curve is obtained using the predictive deconvolution filtering method that deconvolves the theoretical value of volumetric tidal strains from the measured value of well water level. Our results show the response curve is similar to the simulation results of ideal 2D model. Furthermore, the variation of additional volumetric strain caused by regional stress field can be obtained when deconvolving the response curve from measured value of well water-levels after removing the effect of earth tide, barometric pressure, etc. The response curve can be also used to infer the sensitivity of well water level to the dissipation effect. strain variation and dissipation law of abnormity of well water level. It contains information of the well-aquifer system, including hydrogeology properties that are hard to measure directly. Our response curve also indicates that the dissipation process of abnormity needs to be accounted for to accurately infer the variation of volumetric strain caused by the regional stress field.

Key Words
quifer, Earth-tides, Volumetric Strain, Dissipation

Xie, Y., Zhao, Y., & Meng, L. (2016, 08). Using Well Water Level To Measure Volumetric Strain Considering The Dissipation Effect. Poster Presentation at 2016 SCEC Annual Meeting.

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