CHARACTERIZATION OF TOTAL AND EFFECTIVE POROSITY IN EARLY MIOCENE POST-RIFT SANDSTONE RESERVOIRS OF THE “NOIR” FIELD, CENTRAL SUMATRA BASIN

Dias Dwi Aprilia, Ildrem Syafri, Nanda Natasia

Abstract


The Early Miocene post-rift sandstone reservoir of the Sihapas Group represents a key hydrocarbon-producing layer in the Central Sumatra Basin. Reservoir quality within these sandstones is controlled by pore characteristics, mainly total porosity (PHIT) and effective porosity (PHIE), which determine the storage capacity to store fluids and connectivity of pore spaces. This study aims to characterize the allocation of total and effective porosity within the “Noir” field employing well-log analysis supported by conventional core and sidewall core data. The volume of shale (VSH) was determined from the gamma-ray logs utilizing the linear gamma-ray approach. Conversely, the total porosity was assessed from the density logs, while the effective porosity was derived by removing the volume of clay-bound water from the total porosity. The computed porosity values were investigated to assess the reservoir quality of the tested periods. Total porosity (PHIT) is always greater than the effective porosity (PHIE) at all intervals. This is due to the fact that PHIT accounts for the pore spaces filled with clay bound water and shale, while PHIE only takes into account the interconnected pore spaces that are essential for hydrocarbon storage and fluid movement. The maximum mean total porosity is 19.6% and the highest effective porosity of 16.5% are seen in the Top B of Noir-1, indicating that it has the most favorable reservoir characteristics among the tested periods. During this period, Top C of Noir-2 exhibits a dramatic decline in PHIT (16.7%) to PHIE (7.0%), showing that the increased shale content has caused a drop in pore connectivity. Overall, the results indicate that the quality of the reservoir is predominantly controlled by the distribution of shale. In general, cleaner sandstone intervals are characterized by increased effective porosity and improved storage capacity. The findings of this research provide a solid foundation for assessing reservoir quality and contribute to the future exploration and development of hydrocarbons in the Central Sumatra Basin.


Keywords


clay-bound water, density porosity, formation evaluation, pore connectivity, shale volume

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References


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DOI: https://doi.org/10.24198/gsag.v9i3.71677

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