Taylor Polynomial Model of the Geomagnetic Field in an Underground Gas Storage Area

Abstract

The study of normal geomagnetic background fields is the premise and basis for obtaining local geomagnetic anomalies caused by changes in underground pressure during gas injection and extraction in an underground gas storage (UGS) area. Measurements of the total magnetic field in an array consisting of sixty-three stations were acquired at a UGS and its surrounding areas. We completed field measurements at the stations using proton precession magnetometers (PPMs) with a sensitivity of 0.15 nT @ 1 Hz in April 2017 and March 2018. The geomagnetic background field model of the UGS area is calculated using the Taylor polynomial fitting method based on the data of all measured stations. A fourth-order Taylor polynomial model is appropriate for the UGS area according to a comprehensive comparative analysis of the mean square error and boundary distortion effect. The geomagnetic field distribution in the core area of the UGS can be better described by enlarging the network of repeat stations. The results provide a reference model for extracting the variations in the local magnetic field (LMF) caused by the underground pressure variations in the UGS area.