鄂尔多斯盆地镇泾地区长8段致密砂岩油藏成藏孔隙度下限研究

摘要

鄂尔多斯盆地镇泾地区长8段现今含油储层孔隙度和渗透率下限分别为4%和0.03 ×10-3μm2,属于特低孔低渗油藏.主成藏期、成岩作用、埋藏史及模拟实验研究结果表明,高致密油藏缘于成藏后储层致密化.传统方法是通过统计现今含油物性下限作为成藏物性下限,这种方法不适用于成藏后再致密油藏的研究.以现今储层含油物性下限为切入点,利用砂岩孔隙度演化规律,对现今储层含油物性下限进行成藏后孔隙度损失量补偿,从而求取油气成藏孔隙度下限,利用该方法得出镇泾地区长8段石油成藏孔隙度下限为10.5%.研究表明成藏物性下限是镇泾地区长8段成藏的主控因素之一,只有成藏期孔隙度大于成藏孔隙度下限时油气才可能进入圈闭成藏.%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.