An Onshore to Offshore Conceptual Model to Characterise Structural Domain in West Timor Basin

Abstract

Abstract Despite its complex geological and structural conditions, West Timor holds great potential for petroleum exploration. However, a lack of data on the onshore area has made it challenging to fully understand the geological conditions that extend from offshore to onshore. This study aims to develop a geologic conceptual model that unravels the geological and structural complexity in West Timor by extending the geological understanding from onshore to offshore. To achieve this goal, a play-based exploration methodology is employed, which includes geological field mapping and fluid sample analysis in the onshore area, and subsurface mapping using well and seismic data, 2-D palinspastic analysis, and basin modeling in the offshore area. A combination of land and satellite gravity data analysis is used to make basement depth estimations in both onshore and offshore areas, validated by well and seismic data. The geological analysis in the onshore area is then integrated with the analysis in the offshore area to obtain a complete geological understanding that extends from onshore to offshore and differentiates structural domains in the study area. This study is able to construct a comprehensive geologic conceptual model and differentiate four structural domains (SD) in West Timor. These structural domains provide insight into the stratigraphical succession, basement depths, and other structural features that can help explain petroleum systems in the region. SD-1 is a normal horst-graben system, while SD-2 is thin-skinned deformation with a slightly deformed horst-graben system below imbricate thrust-fold system with a detachment surface penetrating Early Jurassic sediment (detachment surface in this domain is Aptian Early Cretaceous-shale of Darwin Fm.). SD-3 is similar to SD-2, but the detachment surface penetrates deeper into Triassic sediment (distal shale as part of prograding toe from Triassic sediment). Lastly, SD-4 is a highly deformed zone where the detachment surface penetrates the basement, resulting in a thick-skinned structure. The onshore area has the most deformed structure zones (SD-4 and SD-3) linked to fold-thrust belt geometry, making it more challenging for petroleum exploration. Meanwhile, the near-shore and offshore areas (SD-2 and SD-1) have less structural deformation. They are considered the most promising areas for hydrocarbon accumulation below imbricate thrust fold system (subthrust), as they still preserve the structural conditions and stratigraphic succession needed for accumulation. The conceptual model constructed in this study offers a deeper understanding of the geologic and structural complexity in West Timor by integrating onshore and offshore data. By characterizing these structural domains, geoscientists can better identify areas with potential for petroleum accumulation and help synthesize a petroleum play concept in this area.