核磁共振测井在川中地区上三叠统低孔、低渗储层评价中的应用

Application of NMRL to the evaluation of low-porosity and low-permeability upper Triassic reservoirs in the central Sichuan Basin

四川盆地中部上三叠统须家河组属典型的低孔、低渗碎屑岩储层,有效储层的识别、储层参数的计算与流体类型的判别存在着较大困难。为此,将核磁共振测井处理结果与岩心分析数据相结合,用谱系数法重新建立了毛细管束缚水孔隙度计算模型,将计算绝对误差控制在0.5%以内;利用岩心分析数据对核磁共振渗透率模型进行了优化,提高了渗透率计算的精度;结合Archie公式,得到了该地区的自由水饱和度计算模型。在准确计算储层参数的基础上,结合试油数据建立了储层识别标准:有效孔隙度大于6%,渗透率大于0.05mD为有效储层;自由水饱和度均值小于10%,极大值小于15%为气层;自由水饱和度均值高于15%,极大值高于20%为水层。对5井次11个储层段进行统计的结果表明,其有效储层的识别结果与试油结果相吻合,流体类型判别符合率在85%以上。

The upper Triassic Xujiahe reservoirs in the central Sichuan Basin are typical clastic reservoirs with low porosity and low permeability so it becomes difficult to identify effective reservoirs,calculate reservoir parameters,or discriminate reservoir fluid types.In order to solve these problems,the following measures are taken.（1） The interpretation of nuclear magnetic resonance logs（NMRL） is integrated with core analysis and the spectrum coefficient method is used to rebuild capillary irreducible water porosity model with an absolute error below 0.5%.（2） The NMRL permeability model is optimized with the core data to improve the accuracy of permeability calculation.（3） The Archie equation is integrated to build a free water saturation model.Based on the accurate calculation of reservoir parameters,formation test data are applied to establish the criteria of reservoir identification.（4） Reservoirs with effective porosity over 6%and permeability over 0.05mD are effective reservoirs;those with the mean value of free water saturation below 10%and its maximum value below 15%are gas-bearing reservoirs;while those with the mean value of free water saturation over 15%and its maximum value over 20%are water layers.The statistics of 11reservoir intervals in 5wells reveal that the identified effective reservoirs match the formation test results and the coincidence rate of reservoir fluid discrimination is over 85%.