In the oil and gas industry, the critical volumetric parameter is porosity, one which allows for the estimation of hydrocarbon reserves, constituting important sources of energy. For unconventional reservoirs such as shales, precise porosity measurement is a challenge due to the significant number of pores with diameters of several nanometers and fewer. In this paper, we focus on the use of the modified Low Field NMR approach, applying a Spin Echo CMPG sequence for the quantitative and precise determination of movable porosity in the full range of the occurring pore distribution. The proposed approach minimizes the impact of overlapping signals originating from hydrogen in organic matter, OH groups, chemically bound water and moving water in the pores on the measured porosities. The examined samples from the Baltic Basin (Poland) were characterized by narrow PSD, with a dominant pore size of 2 nm, which is much lower than those known from the literature for shales, which typically range from several to dozens of nanometers. Results from the modified NMR protocol are compared with porosities from MICP and those obtained using the standard NMR approach with T₂ cut-offs. As evidence of the superiority of the novel NMR approach over the standard NMR procedure, the improved accuracy of the porosity determination for the shales with extremely small pores is presented. Relations between T₂ log-mean and T₁/T₂ values and differential porosity are also presented, suggesting that the LF NMR method could be utilized for rapid porosity estimation with a single T₂ measurement. Correlations between the T₂ time distribution for saturated samples and TOC allowed us to obtain a model with the use of multivariate PLSR analysis, which gives the potential for the NMR method to predict geochemical parameters such as TOC in a simple and non-invasive way.

在石油和天然气工业中，关键的体积参数是孔隙率，它是估算碳氢化合物储量的一个参数，构成了重要的能源。对于诸如页岩之类的非常规储层，精确的孔隙度测量是一个挑战，因为直径为几纳米甚至更少的大量孔隙。在本文中，我们专注于使用改良的低场NMR方法，将自旋回波CMPG序列用于定量和精确确定整个发生的孔隙分布范围内的活动孔隙度。所提出的方法最大程度地减少了由有机物中的氢，OH基，化学结合的水和孔隙中的流动水引起的重叠信号对测得的孔隙度的影响。来自波罗的海盆地（波兰）的受检样品的特征在于狭窄的PSD，主要孔径为2 nm，这远低于文献中已知的页岩（通常为几纳米到几十纳米）。将修改后的NMR方案的结果与MICP以及使用T的标准NMR方法获得的孔隙率进行比较_2个截止点。作为新颖NMR方法优于标准NMR程序的证据，提出了孔隙非常小的页岩的孔隙度测定精度提高。还提出了T ₂对数均值和T ₁ / T ₂值与微分孔隙度之间的关系，这表明LF NMR方法可用于一次T ₂测量的快速孔隙度估算。饱和样品的T ₂时间分布与TOC之间的相关性使我们能够使用多元PLSR分析获得模型，这为NMR方法以简单且无创的方式预测诸如TOC之类的地球化学参数提供了潜力。