Songklanakarin J. Sci. Technol. 42 (4), 844-849, Jul. - Aug. 2020 Original Article 2D electrical resistivity tomography (ERT) method to delineate coal seams: Case studies on lignite and anthracite Khamvanh Phengnaone 1 , Rungroj Arjwech 1* , and Mark Everett 2 1 Department of Geotechnology, Faculty of Technology, Khon Kaen University, Mueang, Khon Kaen, 40002 Thailand 2 Department of Geology and Geophysics, Texas A&M University, College Station, Texas, 77843 United States of America Received: 26 May 2018; Revised: 2 January 2019; Accepted: 6 May 2019 Abstract The 2D electrical resistivity tomography method was used to study the geometry of coal seams at two sites that differ in the local geological setting and type of coal. One site contains a lignite seam whereas the other contains an anthracite seam. The coal seam resistivity signatures were determined and the results were compared between the two study sites. The interpreted 2D resistivity tomograms showed that the lignite seam cannot be distinguished from the surrounding host rocks but the anthracite seam is clearly associated with high resistivity values up to 100 Ωm with respect to the low-resistivity background of shale. The type and age of coal affects the porosity and water saturation. Increases in these two parameters reduce the bulk resistivity of the formation. Type, age, and fluid content are important factors that determine the resistivity contrast of a coal seam with the surrounding rocks. Keywords: electrical resistivity tomography (ERT), lignite, anthracite 1. Introduction Coal is a major energy resource worldwide for electricity generation (Schnapp & Smith, 2012). Its exploitation contributes about 20% of Thailand’s energy needs and that amount is expected to increase in the future (Schmollinger, 2018). In Lao PDR, coal energy supplied about 0.15% of the country's total energy needs in 2010 but the contribution from coal increased to 15.6% in 2015. The demand for coal everywhere is on the rise (Kouphokham, 2013). Besides electricity generation, coal is also used as fuel in other commercial and industrial processes such as cement production, metal smelting, and in the food industry (Schnapp & Smith, 2012). Geophysical methods have long been used for coal exploration. The use of non-invasive geophysics is cost- effective and serves as an excellent complement to conventional geotechnical testing (Anderson, Hoover, & Sirles, 2008; Arjwech et al., 2013; Arjwech & Everett, 2015). The results of geophysics exploration when combined with drill-hole data enables reliable coal mapping for exploration and exploitation (Afonso, 2014; Hatherly, 2013). It is advantageous to perform geophysical prospecting before the coal mining begins (Lei, 2015). The electrical resistivity survey method was first developed in the early 1900’s. It was used for coal investigations as early as 1934 (Ewing, Crary, Peoples, & Peoples, 1936; Tselentis & Paraskevopoulos, 2002). Today, multi-electrode resistivity systems comprise an advanced technology system that is used for mapping a subsurface electrical resistivity structure in two and three dimensions (Dahlin, 2001). Some studies (Singh, Singh K, Lokhande, & Prakash, 2004; Verma, Bandopadhyay, & Bhuin, 1982; Wu, Yang, & Tan, 2016) have demonstrated that the electrical resistivity tomography (ERT) survey method can successfully be used to study coal deposits. Generally, coal has a high *Corresponding author Email address: rungroj@kku.ac.th