Abstract Bakken Petroleum System (BPS) is composed of both conventional and unconventional units, which exhibits significant variations in lithology, rock texture, clay content, total organic carbon, accompanied by high connate water salinity, presence of disseminated pyrite grains, and low values of porosity. These petrophysical attributes of the BPS lead to inconsistency in the oil-in-place estimates for those obtained from Electromagnetic (EM) induction log, Nuclear Magnetic Resonance (NMR) log, dielectric dispersion log measured by Array Dielectric Tool (ADT), and Dean-Stark core measurements. For purposes of improved hydrocarbon saturation estimation and petrophysical characterization in the BPS, a joint-inversion-based interpretation was performed on dispersive electrical conductivity and dielectric permittivity measurements at 4 dielectric-log-acquisition frequencies and 1 induction resistivity acquired at 20 kHz. This analysis was performed across a 350-ft depth interval in one of the science wells intersecting the BPS. Three geo-electromagnetic mixing models, namely Complex Refractive Index model, Stroud-Milton-De model, and Waxman Smits model are integrated and coupled to the inversion scheme to simultaneously estimate water saturation, formation brine conductivity, cementation exponent and saturation exponent in BPS. Water saturation estimates obtained using the proposed interpretation method were compared against those obtained from NMR log, Dean-Stark core measurements and service company’s dielectric inversion. In Middle Bakken from depth XX720 to XX750 ft, our estimates of water saturation are in better agreement with those estimated by service company’s mineral inversion method and service company’s dielectric interpretation as compared to those obtained from NMR interpretation and Dean Stark core measurement. Water saturation and formation brine conductivity estimates in Middle Bakken are in the ranges of 0.5–1 and 25–45 S/m, respectively. Inversion-derived brine conductivity and saturation exponent estimates are most uncertain in Lodgepole and Three Forks 2 formations, which exhibit a wide range of pore size distribution. Average relative errors in matching the 1 induction resistivity and 8 dielectric dispersion logs using the inversion-derived estimates are 33% and 20%, respectively, in the 350-ft depth interval of BPS. The proposed inversion achieves high certainty for the estimates when the formation has low clay content, low electrical anisotropy, and high porosity.

中文翻译：

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基于电阻率和介电色散测井联合反演的巴肯石油系统油气饱和度

摘要 巴肯石油系统（BPS）由常规和非常规单元组成，在岩性、岩石质地、粘土含量、总有机碳方面表现出显着变化，伴随着高原生水盐度，存在播散黄铁矿颗粒，以及低值孔隙率。BPS 的这些岩石物理属性导致从电磁 (EM) 感应测井、核磁共振 (NMR) 测井、由阵列介电工具 (ADT) 和 Dean 测量的介电色散测井获得的那些估计值不一致- 斯塔克核心测量值。为了改进 BPS 中的碳氢化合物饱和度估计和岩石物理特征，在 4 个介电对数采集频率和 1 个在 20 kHz 采集的感应电阻率下，对色散电导率和介电常数测量值进行了基于联合反演的解释。该分析是在与 BPS 相交的科学井之一的 350 英尺深度间隔内进行的。将复折射率模型、Stroud-Milton-De 模型和 Waxman Smits 模型三个地电磁混合模型集成并耦合到反演方案中，以同时估计 BPS 中的水饱和度、地层盐水电导率、胶结指数和饱和度指数。使用建议的解释方法获得的水饱和度估计值与从 NMR 测井、Dean-Stark 岩心测量和服务公司的介电反演获得的值进行了比较。在 XX720 至 XX750 英尺深度的 Middle Bakken，与从 NMR 解释和 Dean Stark 岩心测量获得的那些相比，我们对水饱和度的估计与服务公司的矿物反演方法和服务公司的介电解释估计的那些估计更加一致。Middle Bakken 的水饱和度和地层盐水电导率估计值分别在 0.5-1 和 25-45 S/m 的范围内。反演得出的盐水电导率和饱和度指数估计在 Lodgepole 和 Three Forks 2 地层中最不确定，它们表现出广泛的孔径分布。在 BPS 的 350 英尺深度间隔中，使用反演得出的估计值匹配 1 个感应电阻率和 8 个介电色散测井的平均相对误差分别为 33% 和 20%。