Organic shale is one of the most important unconventional resources all around the world. Total organic carbon (TOC) content is an important evaluation parameter of reservoir hydrocarbon source quality. The regular evaluation methods have higher requirements of well logs and core experiment data for statistical regression. Through analyzing the resistivity and gamma ray logging response characteristics of shale content and organic matters, combined with digital rock physics experiment simulation, we put forward and improve the dual-shale-content method for TOC content logging evaluation. The accuracy of this method is verified by actual data processing. The result shows the dual-shale-content method is simple to use and the error is small. And by comparing with the calculation results by using the ∆LogR method, it is revealed that the trend of the TOC content calculated by our method agrees with the core results better. This new method is suitable for the evaluation of TOC content in the area or interval where there is only conventional logs.
Seepage-induced piping erosion is observed in many geotechnical structures. This paper studies the piping mechanism of gap-graded soils during the whole piping erosion failure process under a supercritical hydraulic gradient. We define the supercritical ratio Ri and study the change in the parameters such as the flow velocity, hydraulic conductivity, and fine particle loss with Ri. Under steady flow, a formula for determining the flow velocity state of the sample with Ri according to the fine particle content and relative density of the sample was proposed; during the piping failure process, the influence of Rimax on the rate at which the flow velocity and hydraulic conductivity of the sample increase as Ri decreases was greater than that of the initial relative density and the initial fine particle content of the sample. Under unsteady flow, a larger initial relative density corresponds to a smaller amplitude of increase in the average value of the peak flow velocity with increasing Ri. Compared with the test under steady flow, the flow velocity under unsteady flow would experience abrupt changes. The relative position of the trend line L of the flow velocity varying with Ri under unsteady flow and the fixed peak water head height point A under steady flow were related to the relative density of the sample.
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