Geochemical characteristics of source rocks and oil-source correlation in the Kashi Sag, Tarim Basin

The Kashi Sag in Tarim Basin shows good hydrocarbon exploration prospects with superior accumulation conditions. However, the only discovery is the Akmomu gas field. One important reason is that there is no clear understanding of hydrocarbon source rocks. Through systematic sampling and geochemical analysis of 9 profiles in the Kashi Sag, we concluded that the Lower Carboniferous and Lower-Middle Jurassic are the main hydrocarbon source rocks in the Kashi Sag. The Lower Carboniferous marine mudstones and marlstones are medium-good hydrocarbon source rocks with type Ⅱ organic matter that are widely distributed with large thickness. They are highly mature and mainly produce dry gas. Lacustrine mudstones of organic matter type Ⅱ in the Middle Jurassic Yangye Formation and swamp facies mudstones of organic matter type Ⅲ in the Lower Jurassic Kangsu Formation are lower quality potential sources. They are mature and mainly produce oil and light oil. Oil-source correlation indicated that the source rocks of Heiziwei oil seepage, Kelatuo oil sand and well Ake1 natural gas is Carboniferous, which is the main source rock sequence in the sag. The Lower-Middle Jurassic source rocks have restricted hydrocarbon generation potential and are distributed locally and were less important for hydrocarbon accumulation.