苏北盆地古近系阜宁组页岩工程品质测井评价

Logging evaluation of the engineering quality of the Paleogene Funing Formation oil shales in the Subei Basin

页岩储层通常无自然产能,需要采用水平井钻井和体积压裂等手段进行商业开采,基于工程品质测井评价的页岩可压裂层段优选工作显得尤为重要。以苏北盆地古近系阜宁组页岩为例,应用阵列声波资料计算泊松比、杨氏模量等岩石力学参数,并与岩心实测资料刻度实现岩石力学参数动静态转换,以此为基础应用泊-杨法和一维岩石力学模型分别计算脆性指数与三轴地应力。综合考虑单井不同层段的脆性指数以及水平主应力差,优选了脆性指数以及脆性指数与水平最大、最小主应力差的比值作为工程品质表征参数。结合试油资料表明对于脆性指数越大、水平主应力差越小的储层,其压裂后产能越高。将苏北盆地阜宁组工程品质划分为两类:Ⅰ类高产(工程品质表征参数>2.2),Ⅱ类中-低产(工程品质表征参数<2.2),并且Ⅰ类工程“甜点”段普遍压裂出油,表明依据该参数的“甜点”分类效果较好。页岩工程品质测井评价结果,可为可压裂性层段的优选提供理论依据与技术支撑,为页岩储层钻井轨迹设计与压裂设计工作提供科学指导。

Shale oil reservoirs,characterized by no productivity,are developed by horizontal drilling and volume fracturing,and it is very important to optimize shale fracable intervals based on engineering quality logging evaluation.The Paleogene Funing Formation shale in the Subei Basin is taken as a typical example in this study.A sonic scanner is used to calculate the elastic parameters,including Poisson′s ratio and Young′s modulus.Dynamic and static parameters are converted through core analysis data.The brittleness index and in situ stress are calculated according to Poisson′s ratio and Young′s modulus.In addition,a one-dimensional rock mechanics model was constructed with the shear slowness in a single well to calculate three components of in situ stress.Finally,considering the difference in the brittleness index and horizontal stress differences between different layers,brittleness index(BI)and(BI/(σH-σh))were selected to describe the engineering quality.According to oil test data,the larger the brittleness index and the smaller the horizontal stress are,the higher the capacity after fracturing.A cross plot of the brittleness index and BI/(σH-σh)is established to divide the reservoir types.Consequently,there are two types,including I high productivity(engineering quality characterization parameters>2.2)andⅡmedium-low productivity(engineering quality characterization parameters<2.2),in the Paleogene Funing Formation in the Subei Basin.High productivity produces oil after fracturing,which suggests that the classification results of sweet spots depending on the engineering quality characterization parameters are better.Logging evaluation of the engineering quality of shale oil reservoirs can provide a theoretical basis and technical guidance for optimizing favorable fracability and high productivity layers and provide scientific guidance for drilling and fracturing layer optimization of shale reservoirs.