Characterizing coal seams hosted in Mmamabula Coalfield, central Botswana using pseudo-3D electrical resistivity imaging technique. (July 2020)

• Record Type: Journal Article
• Authors: Nthaba, Bokani; Shemang, Elisha; Hengari, Amogelang; Kgosidintsi, Boniface; Tsuji, Takeshi
• Is Part Of: Journal of African earth sciences. Volume 167(2020)
• Publication Date: 2020-07
• Subjects: Coal seams -- Electrical resistivity imaging -- Isosurface -- Mmamabula Coal field -- Middle Ecca subgroup; Earth sciences -- Africa -- Periodicals; Earth sciences -- Middle East -- Periodicals; Geology -- Africa -- Periodicals; Geology -- Middle East -- Periodicals; Sciences de la terre -- Afrique -- Périodiques; Sciences de la terre -- Moyen-Orient -- Périodiques; Géologie -- Afrique -- Périodiques; Géologie -- Moyen-Orient -- Périodiques; Earth sciences; Geology; Africa; Middle East; Periodicals; Electronic journals; 556.05
• DOI: 10.1016/j.jafrearsci.2020.103866
• Languages: English
• ISSNs: 1464-343X

Abstract

Abstract: We used 2D and 3D electrical resistivity imaging (ERI) data inversion to locate and characterize the coal seams in Mmamabula Coalfield. The 2D ERI data inversion usually assumes that subsurface geological units (e.g. coal seams) are infinitely continuous in the direction perpendicular to the profiles. However, this assumption might be violated due to the heterogeneous nature of fluvial/deltaic environments. The lateral variation of the subsurface material can be effectively determined in 3D ERI inversion models. In this study, 2D ERI data were acquired along ten parallel profiles trending north-south, then inverted to produce 2D and 3D models. From the 2D ERI inversion results, we observed that the shallower coal seam occurs around a consistent depth of 13.6 m whereas the second observable coal seam occurs at variable depths including at 50 m and 60 m along the two profiles. Discontinuities in coal seams were also identified. However, the information provided by 2D data inversion in such an environment is insufficient to determine the geometry of coal seams as well as to produce accurate and precise resource estimates for future exploitation. As an alternative, 3D data inversion gives better insight on the subsurface geology complexity and significantly resolves the geometry of coal within the study area. The presented 3D inversion results indicate that coal seams are intermittent and alternate well with other coexisting sedimentary units. We also deduced that they trend east-west and are split and adjoined in some areas along the north-south direction. Overall, 3D data inversion result resolves the elongated coal seams in Mmamabula Coalfield and reveals additional information that cannot be determined on 2D ERI inversion results. Highlights: 2D resistivity data inversion inadequately characterizes elongated coal seams. Coal spatial geometry can be elucidated from Full 3D resistivity models/isosurfaces. 3D data inversion helps to precisely asses the complexity of deltaic environments.