Characteristics of Reservoir Formation and the Controlling Factors of Chang 8 Oilbearing Formation in Huaqing Area of Ordos Basin

Key words: 
• Ordos basin

Abstract: This paper applies reservoir fluorescence, reservoir inclusion and analysis of geochemical characteristics of crude oil and reservoir extracts, combined with distribution and contact relation of reservoir and source rock to study the characteristics of reservoir formation and the controlling factors of Chang 8 oilbearing reservoir in Huaqing area of Ordos basin thoroughly and systematically. Chang 8 reservoir has two different colors of fluorescence, the homogenization temperature of inclusion shows two peaks, the maturity of flow crude oil is higher than that of the reservoir extracts, and the reservoir extracts have serious biodegradation, it is shown that there are two stages of reservoirforming in Chang 8 oilbearing formation. According to the evolution history of source rock and homogenization temperature of reservoir inclusion, it can be implicated that the first stage of reservoirforming occurred in Late Jurassic, Chang 7 source rock reached the hydrocarbon generation threshold at the time, the generated oil with low maturity was biodegraded and formed asphalt. Now the oil in the reservoir is mainly mature which was gathered in Early Cretaceous. It is pointed out that the distribution of Chang 8 reservoir is controlled by multiple factors such as sedimentary facies belt, reservoir characteristics, hydrocarbon source rocks, the contact relationship of reservoir and source rock, pore blockage of asphalt etc. Huaqing area is near the depositional  center of the Chang 7 source rock, but the thickness and purity of the source rock is different, source rock thickness and the carrier bed of the reservoir and source rock together control the oil potentials of Chang 8 reservoir, and the dense lithology segment between the reservoir and hydrocarbon source rock may block the migration of the oil to the Chang 8 reservoir. 