The Geochemical Origin, Hydrocarbon Accumulation and Fluids Prediction of Multiple-Phase Reservoirs in the East Tabei Uplift, Tarim Basin, China

Abstract

The Tarim Basin is a large petroliferous region in China, with Ordovician in Tabei uplift as major exploration strata and oil reservoirs as main targets. Recently a giant deep-strata oil-gas field is found in the Hade-Yuke area in the east Tabei uplift. The characters of fluids are complex, showing a lateral co-existence of various reservoir phases including gas reservoir, condensate and oil reservoirs, and so are the oil-gas origin and accumulation process. Based on multiple experimental methods including biomarkers, isotopes and fluids inclusions, and combined with geological analysis, the lateral regular variation of oil-gas characters is obtained. To be specific, gas reservoirs mainly distribute in the east of the study area, showing high GOR (gas-to-oil ratio), high wax content in crude oils and heavy carbon isotopes in gases, while oil reservoirs in the west have decreasing GOR and wax content and lighter carbon isotopes, indicating gradual change of fluid characters. Comprehensive accumulation analysis shows the existence of two episodes of hydrocarbon charging, the early oil charging occurs in the Late Hercynian and the late gas charging in the Late Himalayan. The gases invade from east to west, leading to a gradual variation of fluid characters, and due to the differences of gas invasion extent, the fluid phase changes from oil reservoirs to gas reservoirs. Therefore, the variation of fluid characters is supposed to be a direct result of the alteration of paleo oil reservoirs by a late formed highly-mature dry gas invasion from oil cracking. The secondary condensates are formed from the retrograde condensation of paleo reservoirs. According to the re-construction of the accumulation process, the distribution of fluids is predicted. Gas reservoirs are proposed to be the future main exploration targets in the east deep strata while oil reservoirs in the west, which has obtained recognition from exploration department in the Oil company.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018