Application of transient electromagnetic method (TEM) technique in South-East Asia: Case studies from onshore Sarawak and North Sumatra

Application of electromagnetic methods for oil and gas exploration is developing world-wide. Two main types of electromagnetic (EM) methods are applied: natural source (magnetotelluric – MT) and methods with an artificial source of the EM field (Time-Domain EM – TDEM, Frequency-Domain EM – FDEM). For onshore hydrocarbon exploration the transient electromagnetic method in frequency or time domain mode is highly efficient. The role of EM methods is increasing in areas with poor seismic data quality, non-structural fields and zones with complex sedimentary cover. Joint interpretation of EM data with seismic or other geological data is a way to reduce the risks and optimize the process of geophysical investigation. Using TEM for oil and gas exploration it is possible to study the resistivity of sedimentary layers from surface to basement and additional information can be received from the induced polarization (IP) results. The paper is devoted to application of different combination of EM methods – TEM and EM-IP for oil and gas exploration. Electroprospecting surveys have been performed over one of the blocks in the Southeast Asia i.e. in Sarawak and North Sumatra. Two techniques were used: Transient Electromagnetic Soundings in Time Domain (TEM) and Induced Polarization Electromagnetic method (EM-IP). The objective is to conduct a comprehensive study of the sedimentary cover using TDEM. This includes mapping of zones with potential reservoirs properties from TEM, and to qualify these areas with Induced Polarization (IP) anomalies, usually related to presence of hydrocarbon system.