An effective porosity is defined as the ratio of volume of interconnected pore space to total volume of a porous sample. It controls the magnitude of fluid flow and is a key parameter in the assessment of recoverable resources. However, its accurate measurement in tight formations is challenging, due to their complex pore structure and lithofacies heterogeneity. In this study, porosities of sixteen lacustrine shale samples from the second Member of the Kongdian Formation (Ek2) in the Cangdong Sag, Bohai Bay Basin were measured and compared using multiple methods and sample sizes to compare and contrast the effective porosity results. The methods included helium pycnometry (HP; cubes of 1 cm3 and grains at 500-841 μm), water immersion porosimetry (WIP; cubes), mercury intrusion porosimetry (MIP; cubes), and nuclear magnetic resonance (NMR; cubes). Finally, samples were completely sealed using paraffin for bulk density measurements to evaluate the extent of potential clay swelling in shale samples involving probing fluids. Results from the HP, WIP, and MIP methods for skeletal density, bulk density, and effective porosity with cubic samples were compared. While very similar skeletal densities were found for all three methods, a lower bulk density, and therefore lower porosity, from the MIP approach can be attributed to the experimental conditions (e.g., vacuum efficiency, applied pressure, wettability of water/helium vs. mercury) and the probable presence of pores with diameters larger than 50 μm not measurable by MIP. Furthermore, the HP porosity of granular samples with 500-841 μm grain sizes can be regarded as approaching the total porosity. The complicated relationship between WIP and NMR porosities may result from the heat-induced volatilization of moisture in pores during NMR tests, and countercurrent imbibition of water replacing the residual hydrocarbons during the saturation process for sample preparation in both tests. The swelling behavior of the lacustrine Ek2 shale with water is not significant because of the low content of expansive clay minerals. In summary, the WIP and HP methods are recommended for effective porosity measurement, whereas the NMR and MIP methods are invaluable for the measurement of pore-size distribution, with additional information on the effective porosity.

中文翻译：

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渤海湾盆地湖相页岩油藏有效孔隙度的多种量化方法

有效孔隙率定义为互连孔隙空间的体积与多孔样品总体积的比率。它控制流体流量的大小，是评估可采资源的关键参数。然而，由于其复杂的孔隙结构和岩相非均质性，其在致密地层中的准确测量具有挑战性。本研究对渤海湾盆地沧东凹陷孔店二段（Ek2）16个湖相页岩样品的孔隙度进行了测量和比较，采用多种方法和样本量对有效孔隙度结果进行了比较和对比。方法包括氦比重法（HP；1 cm3 立方体和 500-841 μm 晶粒）、水浸孔隙率法（WIP；立方体）、压汞孔隙率法（MIP；立方体）和核磁共振（NMR；立方体）。最后，使用石蜡完全密封样品以进行体积密度测量，以评估涉及探测流体的页岩样品中潜在粘土膨胀的程度。将 HP、WIP 和 MIP 方法的骨架密度、堆积密度和有效孔隙率的结果与立方体样品进行了比较。虽然所有三种方法的骨架密度都非常相似，但 MIP 方法的体积密度较低，因此孔隙率较低，这可归因于实验条件（例如，真空效率、施加的压力、水/氦与汞的润湿性） ) 以及可能存在 MIP 无法测量的直径大于 50 μm 的孔。此外，粒度为 500-841 μm 的颗粒样品的 HP 孔隙率可以视为接近总孔隙率。WIP 和 NMR 孔隙率之间的复杂关系可能是由于 NMR 测试过程中孔隙中水分的热致挥发，以及在两个测试中样品制备的饱和过程中水的逆流吸收取代了残留的碳氢化合物。由于膨胀性粘土矿物含量低，湖相 Ek2 页岩的含水膨胀行为不显着。总之，推荐使用 WIP 和 HP 方法进行有效的孔隙率测量，而 NMR 和 MIP 方法对于孔径分布的测量以及有关有效孔隙率的附加信息非常有用。在两个测试中，在样品制备的饱和过程中，水代替残余烃的逆流吸收。由于膨胀性粘土矿物含量低，湖相 Ek2 页岩的含水膨胀行为不显着。总之，推荐使用 WIP 和 HP 方法进行有效的孔隙率测量，而 NMR 和 MIP 方法对于孔径分布的测量以及有关有效孔隙率的附加信息非常有用。在两个测试中，在样品制备的饱和过程中，水代替残余烃的逆流吸收。由于膨胀性粘土矿物含量低，湖相 Ek2 页岩的含水膨胀行为不显着。总之，推荐使用 WIP 和 HP 方法进行有效的孔隙率测量，而 NMR 和 MIP 方法对于孔径分布的测量以及有关有效孔隙率的附加信息非常有用。