Organic Matter Characteristics of the Kiliran and Ombilin Oil Shales, Indonesia

Sixteen oil shale samples have been studied by means of organic petrology and pyrolysis. The samples were taken from Brown Shale and Sangkarewang Formations which were deposited in the Kiliran and Ombilin Basins, respectively, during Late Eocene syn-rift phase. The oil shale organic matter of Kiliran Basin is composed of mainly lamalginite and telalginite. The latter likely originate from Botryococcusbraunii. Sporinite, pollen grain and vitrinite are present in lower amounts. Vitrinite reflectance measurement of the oil shale results values averaging at 0.29%. The organic matter in the Sangkarewang oil shale is dominated by lamalginite. Telalginite occurs only in limited numbers. Sporinite, resinite, pollen grain and vitrinitemacerals are also present in lower amounts. The oil shale has vitrinite reflectance values about 0.37%. Rock-Evalpyrolysis data exhibit Tmax 430 °C and 436 °C for Kiliran and Ombilin oil shales, respectively. Vitrinite reflectance and Tmax data suggest that the oil shales are immature, where the maturity of Ombilin oil shale is slightly higher than that of Kiliran oil shale. Total organic carbon (TOC) measurement results values about 5.61% and 5.01%for Kiliran and Ombilin oil shales, respectively. The presence ofB. braunii-derived telalginite in the Kiliran oil shale confirms lacustrine deposition environments of most ofpaleogene source-rocks in Central Sumatra. This organism probably also indicates that the Kiliran lake was less nutrients or less productive than the Ombilin lake. With respect to beneficiation prospect, the presence ofB. braunii-derived organic matter might be one of contributors to the generally higher amounts of TOC as well as pyrolysis yield in the Kiliran oil shale.