Abstract
This study proposes three-phase saturation identification using X-ray computerized tomography (CT) images of gas hydrate (GH) experiments considering critical GH saturation (SGH,C) based on the machine-learning method of random forest. Eight GH samples were categorized into three low and five high GH saturation (SGH) groups. Mean square error of test results in the low and the high groups showed decreases of 37% and 33%, respectively, compared to that of the total eight. Additionally, a universal test set was configured from the total eight and tested with two trained machines for the low and high GH groups. Results revealed a boundary at ~50% of SGH signifying different saturation identification performance and the ~50% was estimated as SGH,C in this study. The trained machines for the low and high SGH groups had less performance on the larger and smaller values, respectively, of SGH,C. These findings conclude that we can take advantage of suitable separation of obtained training data, such as GH CT images, under the criteria of SGH,C. Moreover, the proposed data-driven method not only serves as a saturation identification method for GH samples in real time, but also provides a guideline to make decisions for data acquirement priorities.
Highlights
Reserved gas hydrate (GH) has high uncertainty regarding its kinetic behavior, geomechanical stability, and economic feasibility
X-ray computerized tomography (CT), involves scanning out of a target GH sample during experiments to infer how inner fluids behave in porous media to address the difficulty of understanding what happens in a GH sample directly [13,14,15]
Some of data seem to be deviated from the diagonal line, it can give a high coefficient of determination (SW of Figure 9b)
Summary
Reserved gas hydrate (GH) has high uncertainty regarding its kinetic behavior, geomechanical stability, and economic feasibility. Our previous study has shown reliable applicability of machine-learning for GH saturation identification based on X-ray CT images [16]. Considering the previous machine-learning applications for petroleum engineering and necessity of proper data construction, this paper will suggest how to separate given X-ray CT images for machine-learning applications with SGH,C. It will analyze how data quantity and quality (or construction) function in terms of machine-learning performance.
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