Reservoir characteristics in the LW3-1 structure in the deepwater area of the Baiyun sag, South China Sea
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ORIGINAL PAPER
Reservoir characteristics in the LW3-1 structure in the deepwater area of the Baiyun sag, South China Sea Dashuang He 1 & Dujie Hou 1 & Penghui Zhang 2 & Martin Harris 3 & Julei Mi 1 & Tao Chen 1 & Jinhui Li 1
Received: 25 March 2015 / Accepted: 18 December 2015 / Published online: 24 March 2016 # Saudi Society for Geosciences 2016
Abstract Geochemistry including carbon isotopes, biomarkers, and maturity indexes indicates that the oil and gas in the Liwan 3-1 (LW3-1) structure are derived from source beds in the Enping, Wenchang, and Zhuhai formations (fms.). The major contribution is from the Enping fm. Two major sandstone reservoirs in the LW3-1 structure are present in the early Miocene deepwater turbidite fan of the Zhujiang fm. and the late Oligocene delta front sediments of the Zhuhai fm., where most traps are structural traps and drape anticlines. Faults act as the main migration pathways while permeable sandstone layers are favorable lateral passage systems. Structures formed by diapirism are conducive to oil and gas migration. A combination of faults, the location of the diapir belt, and the structural ridge control the oil and gas migration and accumulation. Sand units 1–3 in the LW3-1 structure share a common temperature-pressure system and gas-oil contact; they are considered to be the same oil- and gas-bearing strata set. Oil and gas injection intensity is higher in sands 1 and 2 than in sands 3 and 4, in which sand 4 is separated from the upper three reservoirs and belongs to a different oil- and gas-bearing strata set. Oil and gas injected
* Dashuang He [email protected] * Dujie Hou [email protected]
1
School of Energy Resources, China University of Geosciences, Beijing 100083, China
2
The Institute of Geophysical and Geochemical Exploration, Langfang, Hebei 065000, China
3
Geology Department, University of Namibia, Private Bag 13301, Windhoek, Namibia
in sands 1–3 migrate vertically along faults, and then migrate laterally to accumulate in highly permeable sands. In sand 4, oil and gas migrate along faults; they accumulate in the trap and form a reservoir with better perseveration of oil and gas compared with the others. Keywords Baiyun sag . Deepwater . Geochemical characteristic . Oil and gas migration . Reservoir characteristic
Introduction The Pearl River Mouth Basin, located in the deepwater slope area in the northern South China Sea, is a Mesozoic-Cenozoic petroliferous basin. The Baiyun sag is a secondary structural unit (as illustrated in Table 1) in the Zhu II depression in the Pearl River Mouth Basin. The sag has an area of more than 2000 km2; a number of gas reservoirs associated with industrial light crude oil and condensate gas reservoirs have been found in the area (He et al. 2012). Most of the Baiyun sag is located in the deepwater area. The hydrocarbon source rocks are deeply buried and the petroleum geology conditions are complicated. Oil and gas migration and accumulation are characterized by multiple stages and periods from multiple sources. In the eastern
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