Xinjiang Petroleum Geology ›› 2021, Vol. 42 ›› Issue (2): 143-151.doi: 10.7657/XJPG20210203

• OIL AND GAS EXPLORATION • Previous Articles     Next Articles

Significance of Secondary Hydrocarbon Generation and Crude Oil Cracking in Paleo-Reservoirs to Hydrocarbon Accumulation:A Case Study of Cambrian Source Rocks in Bachu-Maigaiti Area of Tarim Basin

CAO Zicheng1a(), XU Qinqi1b, YU Tengxiao1b, QIN Hua2, GENG Feng1b, HAO Jianlong1b, DENG Shang3   

  1. 1. Sinopec, a.Northwest Oilfield Company; b.Research Institute of Exploration and Development, Northwest Oilfield Company, Urumqi, Xinjiang 830011, China
    2. Exploration Company, Sinopec, Chengdu, Sichuan 610041, China
    3. Petroleum Exploration and Production Research Institute, Sinopec, Beijing 100083, China
  • Received:2020-05-21 Revised:2020-11-06 Online:2021-04-01 Published:2021-04-02

Abstract:

In order to analyze the relationship between the thermal evolution history of Cambrian source rocks and hydrocarbon accumulation in the Bachu-Maigaiti area, the thermal evolution history and the denudation of unconformity from Hercynian movement to Himalayan movement were rebuilt by analyzing the track chronology of apatite fission. The results demonstrate that secondary hydrocarbon generation took place in the Cambrian source rocks in the Southwest depression during the late Himalayan movement, which was caused by rapid burial and temperature increase since the Paleogene. Influenced by continuously uplifting, most Cambrian source rocks in the Bachu uplift didn’t have the conditions for secondary hydrocarbon generation. The crude oil generated in the Cambrian source rocks from middle Caledonian movement to early Hercynian movement might accumulate and form paleo-reservoirs on a large scale in the Hetian paleo-uplift, and the paleo-reservoir was quickly buried deep and entered a high-temperature environment during early Himalayan movement, which provided favorable conditions for crude oil cracking. The natural gas from highly matured gas reservoirs discovered in the Bachu-Maigaiti area may come from the cracked gas produced by over-matured kerogen that was generated in Cambrian source rocks during secondary hydrocarbon generation and the cracked gas from the crude oil generated in the paleo-reservoirs after deeply burial and temperature increasing in the Hetian paleo-uplift. Therefore, in the Bachu-Maigaiti area, the Cambrian source rocks, which had a relatively low evolution degree during the late Hercynian movement and are currently in the secondary hydrocarbon generation stage, and the paleo-reservoirs, which were at relatively low geothermal temperature in the early stage but recently have high-temperature cracking conditions, are important sources for natural gas accumulation. And the matching among secondary hydrocarbon generation, crude oil cracking product and new traps is the key to late hydrocarbon accumulation in the Bachu-Maigaiti area.

Key words: Tarim basin, Bachu-Maigaiti area, Cambrian, source rock, secondary hydrocarbon generation, paleo-reservoir, hydrocarbon generation evolution, crude oil cracked gas

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