Study on Depositional Environment in “A” Area Based On Log Motifs Characteristics and Vp/Vs and Poisson’s Ratio Trends

Depositional environments for a prospect are usually determined based on the facies shown on well logs and mostly used to predict and explained the occurrences of the hydrocarbon sands extensions. On other note, rock physics is a growing area in the geosciences study as it is proven to delineate facies. This study attempts to relate the depositional environment with rock physics analysis. The study area “A” for this project is located in Central Luconia Basin, Sarawak. The geophysical assessment includes the analysis on depositional environments penetrated by three wells and rock physics crossplots while geological assessment is carried out at the outcrop in Bandar Seri Iskandar, Perak. Based on the result of geophysical assessment, the study area “A” has a pattern of increasing clay or shale content increases from channel, offshore bars, serrated sands and shale to mouth bars. The hydrocarbon-bearing sediments are delineated using the acoustic impedance vs. Vp/ Vs crossplots and Vp/Vs vs. Poisson’s ratio crossplot. Based on the crossplots, the hydrocarbon-bearing sediments in study area “A” has Vp/Vs with average range of 0-0.25 and Poisson’s ratio with average range of 0-0.375. The value of Poisson’s ratio is slightly higher than the values suggested by the established rock physics model which might be caused by thin layering sands. This study therefore shows the importance to link the facies with its rock physics properties.
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