The existence of underground gas storage causes geomagnetic anomaly in this area?

Abstract

Abstract When the stress state of the rock changes, its permeability will also change accordingly, which is the so-called piezomagnetic effect. The piezomagnetic characteristics of rocks are an important and reliable physical basis for the seismomagnetic effect. Based on the experiments of rock magnetism, many scholars have carried out targeted experiments on the relationship between stress and rock magnetism, and achieved many important experimental understandings. As the largest underground gas storage (UGS) in operation in China, the Hutubi UGS has a design storage capacity of 10 billion cubic meters. It is operated periodically every year by gas injecting in summer and gas extracting in winter. During the process of gas injection and gas extraction in Hutubi UGS, the gas well pressure changes up to more than 10 MPa. Periodic injection and extraction operations will induce variations in the in-situ stress field in local areas. Whether these variations can cause local crustal magnetic anomalies is the focus of this paper. An observation network composed of 63 total geomagnetic intensity measuring stations was established in the Hutubi UGS and its surrounding areas, and the geomagnetic anomalies have been systematically observed. Based on the two phases of field observation data in October 2016 and October 2018, a polynomial fitting method was used to obtain the crustal magnetic anomalies in the UGS area. Results show that the existence of the Hutubi UGS has indeed caused the geomagnetic anomaly changes in this areas, the maximum value of the magnetic anomaly is 19 nT. The results of this field observation further confirmed the existence of the piezomagnetic effect in the laboratory and established the internal connection between the meso-scale crustal magnetic anomalies and the underground stress variations.