Structural analysis and seismic stratigraphy for delineation of Neoproterozoic-Cambrian petroleum system in central and eastern part of Bikaner–Nagaur basin, India

Bikaner–Nagaur basin is located in the northwestern part of India and lies on the rising flank of Punjab platform of Middle Indus basin in Pakistan. Existence of Neoproterozoic-Cambrian petroleum system was confirmed by the exploration activities in the western periphery of the basin, whereas vast areas of central and eastern parts remain unexplored. Knowledge of petroleum system in this unexplored part of the basin is limited due to non-availability of data. Recently, 2525 line km of regional 2D seismic data acquired for the first time by Government of India under National Seismic Program (NSP) unlocks the opportunity for comprehensive understanding of subsurface geology in unexplored part of the basin. Present work aims to interpret recently acquired 2D seismic data and integrate with available surface (outcrop) data, gravity and well data (drilled in western part of basin) for unfolding the petroleum system elements, structural configurations and stratigraphic features in the hitherto central-eastern part of the basin. Two Neoproterozoic-Cambrian hydrocarbon plays: (1) Jodhpur and (2) overlying Bilara/Hanseran Evaporite Group (HEG) were envisaged. Both the plays depicted distinctive seismic characteristics, structural alignment and distribution of reservoir, source and seal. Fluvio-deltaic sandstone within Jodhpur group and shallow marine fractured dolomites within Bilara/HEG showed potential reservoir characteristics whereas organic rich laminated dolomites, stromatolites and argillaceous litho-units within Bilara/HEG group have been predicted as prospective source. The Halite layers within HEG group were considered as effective regional seals. Fault bounded anticlinal structures associated with Cambrian compression have been identified as the main entrapment for hydrocarbon accumulation. The basin witnessed long tectonostratigraphic history with two major compressional phases Structures formed by Cambrian compression are likely to be charged as the time of source maturity and peak expulsion was later, during early Mesozoic period. Overall, the study indicates new opportunities and potential accumulation of hydrocarbon in the unexplored part of the basin.

Dinoflagellate biostratigraphy of Eastern Indonesia stratigraphy: key of petroleum exploration success

Several major discoveries in the eastern part of Indonesia (e.g. Tangguh and Abadi) have increased more petroleum exploration interest in the area. These sizeable discoveries encountered gas in the Jurassic sandstone, which is a key reservoir target in the Northwest Shelf of Australia. The Mesozoic sandstone provenance is located in the Australian Continental Plate or also known as the Sahul Shelf. Thousands of wells were drilled in the Sahul Shelf and the stratigraphy in this area is well understood. The extension of the Mesozoic sandstone towards Indonesian territory, with much less well information, is one of the keys of success for petroleum exploration. Refinement of the stratigraphy of the eastern part of Indonesia is crucial to understand the extension.To refine the stratigraphy of Eastern Indonesia, especially for the Mesozoic interval, dinoflagellates play a significant role. Several types of this marine biota have been used by Australian stratigraphers as markers. In the case where stratigraphic tie to Northwest Shelf Australia discoveries, key wells or standard chronostratigraphy, dinoflagellate understanding is critical.Dinoflagellate markers are used to mark several subdivisions of Plover Sandstone. Norvick (2001) used W. indotata and D. caddaensis Maximum Flooding Surfaces to subdivide the reservoir target into upper, middle and lower Plover Formation. These surfaces are named after dinoflagellates. More markers were identified to mark the source rock and seal in the petroleum system. To have a detail correlation from Indonesia to the NW Shelf, understanding of dinoflagellates is crucial.

Delineation of Banyumas Sub-Basins using Gravity Anomaly Based on Trend Surface Analysis Equation

A study using gravity methods in the Banyumas Basin, located in the southern part of Central Java, Indonesia had been conducted to generate a map for regional geological features in sub-volcanic basin related to petroleum system. This study used the first and second-order of Trend Surface Analysis (TSA) to separate gravity anomaly into regional and residual components. Matrix inversion is applied to obtain constants values for both the first and second-order of TSA. To interpret geological features related to oil and gas study, residual components are used for gravity anomaly. Residual anomaly is also compared for both first and second order of TSA with a regional geological map to validate the result. Residual anomaly from the second order of TSA showed a very comparable result to geological features, as shown in the regional geological map, compared to those of the first order of TSA. These results also showed a strong contrast of some important geological features such as the Gabon-Nusakambangan Formation outcrop, Karangbolong outcrop, and the eastern part of the south Serayu mountain arc. This study also displayed two potential subbasins i.e Citanduy and Majenang sub-Basin that might be a possible setting in which source rocks of the Banyumas Basin were deposited. From this study, it can be concluded that TSA showed a reliable result of separating gravity anomaly data set into regional and residual components.Keywords: Gravity anomaly, Banyumas Basin, petroleum system, trend surface analysis (TSA).