Abstract:

Lower cutoff values of the porosity and permeability of oil-bearing reservoir are as low as 4% and 0.03×10-3 μm² within Chang-8 Member which is typically high-tight reservoir in Zhenjing area. The integrated study of oil accumulation stages, diagenesis, burial history and simulation experiment reveals that the genesis of the high-tight oil reservoir is largely due to strata getting tighter after hydrocarbon accumulation. Traditional method which takes the statistical lower cutoff of current oil-bearing property as the critical physical property of oil accumulation does not be applied in tight sandstone reservoir. This paper presents a new approach to assess the lower limit value of porosity for oil accumulation, by taking porosity evolution of sandstone into consideration, and adding the loss of porosity after oil accumulation to current lower cutoff value of oil-bearing properties. The study shows that the lower limit value of porosity for oil accumulation in Chang-8 Member in Zhenjing area is 10.5%. Statistics indicates that the value is the main control parameter for oil accumulation in this reservoir, and oil could not accumulate until the porosity exceeds accumulating lower limit value. 

Key words: Zhenjing area, genesis of tight sandstone reservoir, lower limit of porosity for oil accumulation, main control parameters for oil accumulation;Ordos Basin