An Update : Northwest Palawan Basin Modeling

Cielo F. Bastero

Philippine National Oil Company – Exploration Corp.
2F Bldg. 1 Energy Center, Fort Bonifacio, Taguig 1634

Abstract

Recent developments and renewed interest in the NW Palawan Basin necessitate an updated basin model of the area which we attempt to provide with this study. The current basin modeling integrates tectonic history (including structural and thermal history), sequence stratigraphy, facies variation, water depth and accommodation space from which information and analysis of potential reservoirs, seals and source rocks can be identified.

The objective of this study is to define the peak oil window in the NW Palawan Basin using PRA’s BasinMod 1D software. Ten wells were used based on available data such as the interpreted stratigraphy, porosity, bottom hole temperatures and vitrinite reflectance. From this information, reconstruction of burial and thermal history was made for each well to estimate time and depth at which the assumed source rocks have matured; it may give an idea at which time maturity has occurred for the whole basin. Heat flow was used as boundary condition, which was calculated from the calibration of bottom hole temperatures of the studied wells, and was dependent on the heat capacity of the rock units.

Previous basin modeling studies indicate that there is sufficient evidence of a petroleum system in the basin. In this modeling exercise, early maturity of source rocks has been attained. The generation-migration-accumulation process may have started in the Middle to Late Miocene and continues to the present. The critical moment, regarded as the time of peak generation of hydrocarbon, is placed at the Late Miocene time with preservation starting at about 5 Ma.

The results of the study are significant for petroleum exploration in the NW Palawan Basin as it verifies a probable timing event for the existing petroleum system. The perceived source rocks, Nido and Synrift (Pre-Nido Sequence), are identified to be within the oil window and peak maturity at an average depth of ten thousand feet. This information can be cross-referenced with seismic data and later help in ranking prospects. This also gives additional support to the Synrift as a good source rock sequence, in terms of heat flow, since it has attained deeper burial.

Further studies are recommended due to constraints on data availability for each well. For example, vitrinite and porosity data are mostly limited to target formations, which are compensated by proper calibration. Acquisition of new data (e.g., vitrinite reflectance) will provide better control of the wells, and therefore, the basin.