页岩油资源规模分布模型及敏感性研究

评价非常规油气资源一般采用类比法、统计法和成因法，在不断创新评价方法的同时，如何将常规油气资源评价方法改进，并应用于非常规资源评价是目前研究的一个重点和难点。以井为单元，将单井估算最终可采油气量（EUR）作为单元油气储量，建立帕累托分布模型，利用随机取样和偏态抽样原理编写程序，分析自然总体个数、形状参数和勘探系数对模型的敏感性，建立了新的页岩油资源规模分布法。该方法应用于鄂尔多斯盆地合水地区X230井区页岩油资源评价，发现数量影响油藏规模分布形状参数的大小和离散程度，当油藏发现个数大于300个时，分布模型趋于稳定；而分布模型对勘探系数的敏感性很小，这是划分EUR为评价单元的局限性所致，因为这种划分方法不存在真正意义上的“大油藏”。通过自然总体个数随形状因子的变化，确定截断点对应的个数，即所有井EUR的总和为该区的可采资源量，为6.72×106 t，这与油气资源丰度法评价结果相吻合。改善后的页岩油资源规模分布法可为非常规油气资源评价提供指导。 

Shale oil size distribution models and their sensitivities

With the rapid development of unconventional oil and gas resources, the demand for corresponding evaluation methods is increasing. At present, the evaluation methods for unconventional oil and gas resources are divided into analogy, statistical and genetic method. While constantly innovating evaluation methods, how to improve conventional methods and apply them to unconventional resource evaluation is also a focus and difficulty in current research. Taking a well as an unit and the EUR of the well as the unit's oil or gas reserves, a Pareto distribution model was established, and a program was compiled according to the principle of random sampling and skew sampling to analyze the sensitivity of number N, shape parameter and exploration coefficient E to the model. This method was applied to the shale oil resource evaluation in the X230 well block in Heshui area of Ordos Basin. Results show that the number of discoveries affects the size and dispersion of the parameters for oilfield distribution. The distribution model tends to be stable when the number is more than 300. Exploration coefficient has little influence on the sensitivity of distribution model, which is the limitation of taking EUR as evaluation unit. According to the variation of number N with shape parameter β, the number corresponding to cut-off point can be determined, that is, the sum of EUR of all wells is the recoverable resource of the area, which is 6.72×106 t. The result is consistent with the evaluation of oil and gas resource abundance. This method can provide guidance for unconventional oil and gas resources evaluation.