| Author's Name: JIANG Haijian1,2, JIANG Hong1,2, ZHANG Wei3, LI Chuntang3, WANG Jie1,2,
ZHU Jianhui1,2, WANG Ping1,2, ZHANG Yi1,2 |
| Institution: 1. Wuxi Institute of Petroleum Geology, SINOPEC Research Institute of Petroleum Exploration and Production; 2. SINOPEC Key Laboratory of Hydrocarbon Accumulation; |
| Abstract: |
| In recent years, natural gas exploration breakthrough has been made in the Ordovician Majiagou Formation of
Ordos Basin, but the formation and evolution of natural gas have not been thoroughly studied. Taking Daniudi gas field as
an example, the typical characteristics of oil-cracked gas in Majiagou Formation are determined through the identification
of bitumen in the core and thin section, the occurrence of hydrocarbon inclusions and Raman spectroscopy testing, and the
analysis of geochemical data of natural gas. The formation conditions of oil-cracked gas are comprehensively analyzed,
and the formation and evolution process of oil-cracked gas in Majiagou Formation are analyzed through the simulation of
burial history and thermal history. The results show that: (1) Bitumen filling with diverse occurrences is found in the
fractured porous reservoir of Majiagou Formation, and it is a dry bitumen with high degree of thermal evolution. Three
phase hydrocarbon inclusions of oil, gas and bitumen are captured in calcite veins of Majiagou Formation, which confirms
the existence of oil cracking gas process. (2) Based on the crossplot of geochemical index such as ln(C1/C2) and ln(C2/C3) of
natural gas, it shows that the internal natural gas of Majiagou Formation is mainly oil-cracked gas. (3) During the
deposition period of 3rd member of Majiagou Formation, Daniudi and its surrounding areas were situated at the margin of a
saline depression, where thick source rocks of argillaceous dolomite and dolomitic mudstone developed with interbedded
evaporates, creating favorable conditions for thermochemical sulfate reduction (TSR). (4) In the Early Jurassic, source
rocks produced a large amount of oil. Under the effect of the relatively high paleotemperature in the Early Cretaceous,
high-temperature oil cracking occurred, and TSR reaction occurred with significantly increased H2S content in the natural
gas of O1m55
-O1m56 of Majiagou Formation in Daniudi gas field. (5) In Daniudi and surrounding areas, the source rocks of
Majiagou Formation became mature earlier in the south and later in the north, and natural gas mainly migrated and
accumulated from south to north along the strike-slip faults. This study has certain significance for the internal gas
exploration of Majiagou Formation in Ordos Basin. |
| Keywords: carbonate rock; oil type gas; oil cracked gas; hydrocarbon accumulation; Majiagou Formation; Ordos Basin |
|
投稿时间：
2025-06-30 |
|
