Abstract: For offshore oilfields, the economic threshold is high and the lower limit of reservoirs for industrial development is difficult to be determined. At present, the development of low permeability oilfields is mainly driven by the development of reservoir "sweet spots". Therefore, it is essential to identify the sweet spots of offshore low permeability oilfields. By analyzing plenty of laboratory experimental and production test data in Beibuwan oilfield of western South China Sea, it is clearified that the difference in the microscopic pore throat structures of different reservoirs is the main factor affecting the flow capacity of low permeability reservoirs. Using geostatistic and cluster analysis methods, this paper selects the key parameters for characterizing low permeability reservoirs, establishes the relationship between the reservoir quality index and the microscopic parameters and flow capacity of the reservoir, quantifies the classification boundaries of the five types of low permeability reservoirs, then establishes a classification and evaluation method of low permeability reservoirs based on gray correlation theory, and quantitatively evaluates the reservoir quality of the low permeability blocks in Beibuwan oilfield. Additionally, a reasonable economic evaluation model has been established according to the productivity evaluation method and production decline law of low permeability oilfields in Beibuwan oilfield, in combination with regional economic evaluation parameters and development models. By introducing the reservoir value factor to draw an evaluation plot for the industrial development of sweet spots in offshore reservoirs, it is determined that type III reservoir indicates the lower limit of reservoir "sweet spots" for industrial development in the Beibuwan oilfield, and the evaluation results match the actual development of the oilfields. Moreover, according to the regional law of the low permeability blocks of Beibuwan oilfield, the lower limit of the effective permeability for the industrial development of reservoir "sweet spots" is determined to be 1.1-1.6 mD.

Key words: Beibuwan Basin, low permeability oilfield, reservoir classification and evaluation, productivity evaluation, reservoir value factor

摘要： 海上油田经济门槛高、工业开发下限难以确定。目前，主要通过储层"甜点"的开发带动低渗透油田的建产，因此，海上低渗透油田储层"甜点"的识别十分重要。通过分析南海西部北部湾油田大量室内实验和生产测试资料，明确储层微观孔喉结构的差异是影响低渗透储层渗流能力的主要因素。利用地质统计学方法和聚类分析方法筛选出表征低渗透储层特征的关键参数，建立储层品质指数与储层微观参数和渗流能力的关系，量化5类低渗透储层的分类界限，进而基于灰色关联理论建立低渗透储层分类评价方法，定量评价了北部湾油田低渗透区块的储层品质，并根据北部湾低渗透油田产能评价方法和产量递减规律，结合区域经济评价参数与开发模式建立合理的经济评价模型。通过引入储层价值因子绘制海上储层"甜点"工业开发评价图版，确定北部湾油田能够实现工业开发的储层"甜点"下限为Ⅲ类储层，评价结果与油田实际开发情况匹配。同时，根据北部湾油田低渗透区块的区域规律，确定储层"甜点"工业开发的有效渗透率下限为1.1~1.6 mD。

关键词: 北部湾盆地, 低渗透油田, 储层分类评价, 产能评价, 储层价值因子