Evaluation of characteristic values of geotechnical parameters (used for oil well design) is associated with uncertainties inherent to the geological processes that change soil strata. Statistical analysis of soil data allows one to deal rationally with these uncertainties. This work addresses some normative recommendations and literature models for statistical characterization of undrained shear strength and submerged unit weight in offshore soils, providing more information to conductor casing design. Three methodologies were selected for the analysis. The NORSOK G-001 (2004) standard recommends using mean values computed conservatively. Lacasse et al. (2007b) propose that the characteristic value should be the mean value minus one-half of a standard deviation of the parameter under analysis. DNV-RP-C207 (2012) suggests different methodologies for dependent and independent soil variables, though both methods of calculating the characteristic value involve linear regressions. Using data from geotechnical investigations that characterize eight oil wells located in two Brazilian offshore basins, the selected methodologies were applied to obtain the characteristic values and compared to each other. The analysis is carried out with data from 17 piezocone penetration tests (CPTu) associated with the eight wells mentioned above. It is noted that the NORSOK recommendation leads to the highest characteristic values, which are assumed tending to the mean value of the data set over the well depth. The values obtained using Lacasse et al. (2007a, 2007b) methodology are more conservative than NORSOK methodology and stand as its lower bound. The models suggested by DNV perform differently when applied to the geotechnical parameters. The dependent variables methodology fits both undrained strength and unit weight accurately. Analysis shows that undrained strength is better described using the methodology for standard deviation proportional to the depth, while for the unit weight, accurate results are obtained by using constant standard deviation. The lower bound procedure proposed by DNV provides, in general, higher results in the first meters and more conservative values along the depth when compared with the other methodologies. Regarding all the formulations addressed, differences between them increase for wells whose CPTu data present higher dispersion. This larger dispersion suggests applications of different statistical-based approaches in order to reliably characterize offshore soil data. The data sets analyzed comprise different levels of scattering and soil heterogeneity, and comparing the statistical recommendations brings additive information for the designer to set the characteristic values of soil properties, aiming for the decision-making process on top hole drilling applications (e.g., conductor casing design). To the authors’ knowledge, few papers perform this comparative analysis.

评估岩土参数的特征值（用于油井设计）与改变土壤地层的地质过程固有的不确定性有关。对土壤数据的统计分析使人们可以合理地处理这些不确定性。这项工作提出了一些规范性建议和文献模型，用于统计表征近海土壤的不排水剪切强度和淹没单位重量，为导体套管设计提供了更多信息。选择了三种方法进行分析。所述NORSOK G-001（2004）标准建议使用保守计算平均值。Lacasse等。（2007b）提出，特征值应为被分析参数的平均值减去标准偏差的一半。DNV-RP-C207（2012）提出了针对土壤变量和独立变量的不同方法，尽管两种计算特征值的方法都涉及线性回归。利用来自岩土工程调查的数据，这些数据对位于两个巴西近海盆地的8口油井进行了特征分析，所选择的方法被应用于获得特征值并相互比较。使用来自与上述8口井相关的17个压电锥渗透测试（CPTu）的数据进行分析。注意，NORSOK推荐会导致最高的特征值，假定这些特征值趋于在井深范围内达到数据集的平均值。使用Lacasse等人获得的值。（2007a，2007b）方法比NORSOK方法更保守，并处于下限。DNV建议的模型在应用于岩土参数时表现不同。因变量方法可准确拟合不排水的强度和单位重量。分析表明，采用与深度成正比的标准偏差的方法可更好地描述不排水的强度，而对于单位重量，使用恒定的标准偏差可获得准确的结果。与其他方法相比，DNV提出的下限过程通常在前几米提供更高的结果，并且沿深度提供更保守的值。对于所有涉及的配方，CPTu数据呈现较高分散度的井之间的差异会增加。这种较大的分散性建议应用不同的基于统计的方法，以便可靠地表征海上土壤数据。分析的数据集包含不同程度的散射和土壤异质性，比较统计建议可为设计人员提供附加信息，以设置土壤特性的特征值，以针对顶孔钻井应用（例如，导体套管）的决策过程设计）。据作者所知，很少有论文进行这种比较分析。旨在进行顶孔钻探应用的决策过程（例如，导体套管设计）。据作者所知，很少有论文进行这种比较分析。旨在进行顶孔钻探应用的决策过程（例如，导体套管设计）。据作者所知，很少有论文进行这种比较分析。