核磁共振测井在低阻油层评价中的应用——以准噶尔盆地阜东斜坡头屯河组为例

摘要

为了解决常规测井方法难以有效识别低阻油层的难题,以准噶尔盆地阜东斜坡头屯河组为例,应用核磁共振测井技术划分和评价低阻油层.利用核磁共振、阳离子交换容量以及岩石薄片、粒度分析等资料研究低阻油层的成因,在此基础上运用核磁共振T2谱定性识别油水层,计算孔隙度、渗透率以及含水饱和度.头屯河组储集层虽然泥质、黏土矿物含量整体上不高,但其特殊的黏土矿物组成能够产生较高的附加导电性和束缚水含量,造成了油层电阻率普遍小于6Ω·m,呈低电阻率的特征.根据核磁共振T2谱形态,参照200 ms处有无谱峰可以有效划分出油层、含水油层、含油水层和水层.以3 ms作为T2截止值,结合岩心实验测得的孔渗关系,可计算低阻油层孔隙度和渗透率,最后将核磁共振测井计算的阳离子交换容量带入W-S模型确定低阻油层含水饱和度.此方法对低阻油层的定性识别和定量评价结果与实验数据相吻合,在生产中具有较好的适用性.%To solve the problem that conventional logging methods can't be used to effectively identify low-resistivity reservoirs,taking Toutunhe formation on the eastern Fukang slope of Junggar basin,the paper uses the NMR logging technology to classify and evaluate lowresistivity reservoirs.Based on the data of NMR,cation exchange capacity,thin section and grain size analysis,the paper studies the genesis of the low-resistivity reservoirs.Based on which,NMR T2 spectrum is used to identify oil intervals and aquifers and to calculate porosity,permeability and water saturation.Although the reservoir of Toutunhe formation contains a small amount of mud and clay minerals,the special clay mineral constitution of the reservoir can generate relatively high additional electrical conductivity and high irreducible water content,which results in the resistivity of oil zones generally lower than 6 Ω· m and the oil zones showing a low-resistivity characteristic.According to the shape of NMR T2 spectrum and whether there is a peak spectral at 200 ms,oil interval,water-bearing oil interval,oil-bearing water interval and aquifer can be effectively classified.Taking 3 ms as the cutoff of T2 and combined with the porosity-permeability correlation obtained from core experiments,the porosity and permeability of the low-resistivity reservoirs can be calculated,finally the cation exchange capacity calculated from NMR logging is substituted into a W-S model to determine the water saturation of the low-resistivity reservoir.The qualitative identification and quantitative evaluation results of the method for the low-resistivity reservoirs well matche with the experimental results,showing a good applicability in oil production.