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Main Controls on Oil Accumulation in Tight Sand Reservoir: A Case Study from the Tight Sand Oil Reservoir, China

Hu, Haiyan *1
(1) School of Geosciences, Yangtze University, Jingzhou, China.

Commercial oil production in the Jurassic Formation tight sand reservoir of Junggar Basin, China has been paid great attention by Chinese geologists. The understanding of main controls on oil accumulation in the tight sand oil reservoir is crucial to oil resource assessment. In this study, the source of oil, reservoir evolution, oil filling history were investigated by GC-MS oil compositional characterization, core thin-section lithological observation, fluid inclusion analysis, carbon isotopic analysis of oils. The core samples from three wells located in three different blocks were examined.

There are two main source rocks in the Junggar Basin, China. One is the Permian lacustrine facies, which is characterized by Pr and Ph ratio less than 1, 13C value of kerogen less than -30‰ , high Gammacerane index and high Previous HitBetaNext Hit-dammarane content. The other is the Jurassic coal bed deposited in the paludal facies, which is characterized by Pr and Ph ratio larger than 3, 13C value of kerogen greater than -27‰, a trace amount of Gammacerane and Previous HitBetaNext Hit-dammarane. The crude oils and extractives of sand from three wells Y1, C1 and D1 located in three different blocks were collected and similar geochemical analysis were examined. The biomarkers and isotopic values show that the producing oil of Y1 well is mainly originated from the Permian source rock, in contrast, the producing oil in C1 and the extractives of sand from D1 wells are originated from the Jurassic source rock.

The fluid inclusion homogenization temperature and buried history studies showed the Jurassic reservoir of Y1 oil producing well was buried in shallow depth of 1800-3100m when oil was charged. The reservoir retained about 14-18% high porosity according to the porosity evolution historical Previous HitcurveTop based on basin modeling and diagenesis study. High porosity provides available spaces for oil accumulation, as a result, high oil flow acheives. In contrast, the Jurassic reservoir of C1 and D1 oil producing well was buried at deep depth of 2300-4800m when oil was filled in. The reservoir’s porosity is low and ranges from 7-14%, which is disadvantageous to pool oil. As a result, non-commercial oil flow and even dry hole wells achieve after drilling test in C1 and D1wells. Our results suggest that commercial oil accumulation in tight sand reservoirs is up to reservoir quality and abundant supply of oil from its source in the course of oil charging.


AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California