CHEMOSTRATIGRAPHY OF THE PERMIAN SEDIMENTS IN BINTUNI AREA, PAPUA BARAT PROVINCE

摘要

Permian sediment penetrated by several wells in Bintuni area mainly are non-marine facies. Gas was discovered in this interval at Vorwata-1 and Mogoi Deep-1 wells with fluvial to deltaic settings. Biostratigraphic analysis allows stage to sub-stage inter-well correlation and paleoenvironment interpretation but uncertainty remains when biostratigraphy is poor, due to lean fossil recovery or no diagnostic taxa were recovered, and seismic does not support due to quality and structural complexity, to guide inter-well correlation. Alternative tools are needed to better constraint the stratigraphy correlation of this interval. BP has completed Chemo-stratigraphy analysis to improve the stratigraphic correlation in problematic interval in the area. Data were acquired for 49 elements in 620 core and cuttings samples from 10 wells by inductively-coupled plasma-optical emission spectrometry (ICP-OES) and inductively coupled plasma-mass spectrometry (ICP-MS). Four chemo-stratigraphy sequences are suggested and look to be correlable across the area. These sequences are characterized based on changes in the key elements ratios of Cr/Al, Cr/Th, K/Rb. Integration with additional key elements ratios of Nb/Ni, Ta/Al, Zr/Cr can further sub-divide the interval into 16 chemo-stratigraphy packages. Several maximum flooding surfaces (MFS) candidates are identified by utilizing FS ratio (U/Al ~* U/Zr) which is used as a proxy to infer organic content. While Ga/Rb ratio as weathering indicator can be tentatively used to identify sequence boundaries (SB) candidates. The whole rock sandstone chemical analysis suggests the sediments most likely were sourced from an acid to intermediate provenance. Chemo-stratigraphy is a useful tool. However, integration with other tools such as biostratigraphy, core description, log curve correlation, seismic etc is required to develop a robust stratigraphic correlation and analysis.