首页|Nature of the Lower-Middle Ordovician reservoir bitumen in the Shunnan area, Tarim Basin, northwestern China
Nature of the Lower-Middle Ordovician reservoir bitumen in the Shunnan area, Tarim Basin, northwestern China
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The Lower-Middle Ordovician reservoir bitumen (RB) results from various geological events (deep burial of strata, volcanic activity and thermocliemical sulfate reduction) in the Shunnan area, Tarim Basin. The understanding of its characteristics and origins sheds light on the accumulation process of hydrocarbon reservoirs. A combination of polarizing microscopy, fluorescence microscopy, and laser Raman microspectroscopy was used to study the characteristics and origins of the RB. In the wells (SN4 and SN7) with obvious hydrothermal activity, the occurrence of RB in each formation includes stylolites accompanied with silicification in the microcrystalline limestone of the Yijianfang (O_(2yj)) Formation, stylolites and dissolution pores in the granular limestone of the Yingshan ((O_(2yj)) Formation, and stylolites and intercrystalline pores of saddle dolomite in the limy dolomite of the Penglaiba (O1p) Formation. In the wells (SN5, SN501, SN5~(-2), and SN6) without hydrothermal activity, the occurrence of RB in each formation includes stylolites in (O_(2yj) and Oi_2y Formations and stylolites and dolomite intercrystalline pores in O1p. Moreover, the RB contents of the wells with hydrothermal activity are about two times as large as those of the wells without hydrothermal activity in each formation. From (O_(2yj) to O_(1 2y) and then to O1p, the effect of hydrothermal activity and dolomitization on reservoir transformation is gradually enhanced, and the RB content is gradually increased. In addition, the average maturity of the RB (Ro%caic) in wells SN4 and SN7 is 2.2196~(-2).36%, whereas that in wells SN5, SN501, SN5~(-2), and SN6 is 1.90%~(-2).11%. The cracking of deeply buried crude oil is the key factor controlling the widespread distribution of RB. The hydrothermal activity in Early Permian produced abnormally high maturity of the RB in wells SN4 and SN7. Thermocliemical sulfate reduction (TSR) promoted the cracking of crude oil, which had a positive impact on the formation of RB.
Accumulation and reconstructionCarbonate reservoirOccurrenceFluorescenceMaturityOrigins
Hua Liu、Yu-Wei Yang、Bin Cheng
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Shandong Provincal Key Laboratory of Deep Oil and Gas, China University of Petroleum, Qingdao, 266580, China
NSTL
