Laser Particle Size Analysis (LPSA) approachment for Depositional Environment and Hydraulic Flow Unit (HFU) determination in Keutapang Formation, Rantau Field (North Sumatera Basin) and Air Benakat Formation, Tempino Field (South Sumatera Basin)

Keutapang Formation deposited in North Sumatra Basin at the mid to late miocen on regression phase. Air Benakat Formation deposited in South Sumatra Basin, has similar characteristic with Keutapang Formation which deposited in the regression & compressional phase near the same age. The purpose of this study is to know the relationship between Laser Particle Size Analysis (LPSA) and Depositional Environment to include Hydraulic Flow Unit (HFU) in each Formation to help reservoir characterization process and rock type determination. Laser Particle Size Analysis results show that both formations have grain size from 11 to 160 μm in other words is very fine sand (wentworth scale). Sorting ranges from 1.5 to 2.4Ø which is classified as poorly sorted to very poorly sorted. Skewness ranges from -0.091 to 0.658 Ø grouped into near symmetrical, fine, and very fine skewness. Kurtosis ranges from 0.686 to 1.102 Ø grouped into very platykurtic, platykurtic, and mesokurtic. Based on the Linear Discriminate Function (LDF) method, by evaluating the values of Y1, Y2, Y3 and Y4, it describes that both formations are deposited on the Deltaic Environment with Shallow Agitated Water and dominated by traction currents. Difficulties in geomodelling process comes when there is no relationship between log analysis properties (which will be distributed) with HFU (from core data analysis). With LPSA data, we can obtain a linear (indirect) relationship between grain size and the shale volume on the same rock geometry. This relationship can be used to distribute HFU values by using a plot of grain size with HFU or Flow Zone Index.