Differences in marine hydrocarbon accumulation between the eastern and western parts of Shunbei area, Tarim Basin

From the eastern to the western part of Shunbei area in the Tarim Basin, the accumulations of marine oil and gas obviously decrease with the exploration risks significantly increasing. To find out the reason for the differences, the oil and gas accumulations in the eastern Shunbei area on the western margin of Manjiaer Depression and the western Shunbei area on the eastern margin of Awati Depression were analyzed, and the differences of accumulation conditions were discussed. In recent years, the eastern part of Shunbei oil and gas field, which is represented by the northeastern section of Shunbei No.1, 4 and 8 belts, has continuously achieved high yield with multiple stages of oil and gas accumulations and obvious oil and gas enrichment characteristics. While in the western part of Shunbei area, only early-stage accumulations with small scale were discovered. There are differences in the distribution conditions of source beds, hydrocarbon generation evolution history, source resource scale, reservoir-forming period and reservoir-forming mode between the eastern and western parts of Shunbei area, which leads to multi-source and multi-stage accumulation in the east and single-source and single-stage accumulation in the west. Adjacent to the Manjiaer hydrocarbon-generating depression, the eastern part of Shunbei area has favorable accumulation conditions such as pathways for vertical migration, targets for hydrocarbon migration of various sources, qualified cap rocks and lateral sealing, and multiple stages of hydrocarbon generation with strong intensity, resulting in multi-source and multi-stage accumulation. While in the western part of Shunbei area, there is single-source and single-stage accumulation sourced from either local Cambrian Yurtus Formation or Ordovician in the Awati Depression. Breakthroughs in Ordovician in the Yingmaili Oilfield on the eastern margin of Awati Depression and well Yingxi 1 in recent years indicate that the accumulation of marine oil and gas mainly took place in the late Hercynian period, and partially in Himalayan period. Generally speaking, the development of source rocks around the Awati Depression is relatively poorer, and the distribution of marine oil and gas as well as the scale of hydrocarbon resources are limited.