Understanding mechanical behaviour of shale is essential for efficient shale gas extraction, which can vary in different depositional settings. The impact of sedimentary environment on shale characteristics, such as mineralogical composition, total organic carbon content (TOC), and petrophysical properties, has been extensively researched. However, its influence on shale mechanical properties, especially in defining mechanical stratigraphy for targeting specific fracturing intervals, remains less explored. In this study, the influence of depositional environment on the mechanical properties of shale samples from the Rajmahal Basin is evaluated. Tensile strength of the samples was measured by the Brazilian splitting tensile strength and the brittleness index was calculated as a measure of mechanical properties. In addition, inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray fluorescence spectroscopy (XRF), Rock-Eval 6, and X-ray diffraction (XRD) analysis were carried out to assess geochemical characteristics of the samples from different perspectives. The results revealed that such geochemical variations that are generally controlled by the depositional environment, would impact the mechanical properties of the samples. Based on major and trace elements proxies, the depositional environment was determined to be passive continental margin, with hot and humid paleoclimatic conditions and freshwater anoxic settings. Tensile strength and brittleness index of the shale samples was observed to vary between 0.93 and 4.12 MPa and 0.71 to 3.40, respectively, while samples with the TOC exceeding 15 wt% had a strong negative correlation with tensile strength, as reasonably expected, due to weakening impact of the sedimentary organic matter on the shale matrix. Tensile strength and brittleness index correlated positively with clay mineral content, particularly their type, but negatively with the quartz content. Furthermore, samples abundant in biogenic silica exhibited reduced brittleness compared to those with lithogenic silica. Nevertheless, the variation in mechanical properties with burial depth was not substantial, and the examination of stress-strain curves indicated an overall brittle nature of the layer where the samples were retrieved from. Overall, achieving more robust conclusions regarding mechanical stratigraphy within the studied section of the Rajmahal Basin, would necessitate additional vertical sampling.

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印度拉杰马哈尔盆地巴拉卡页岩机械地层的沉积环境控制

了解页岩的机械行为对于有效提取页岩气至关重要，因为不同的沉积环境下页岩气的机械行为可能会有所不同。沉积环境对页岩特征（如矿物成分、总有机碳含量（TOC）和岩石物理性质）的影响已得到广泛研究。然而，其对页岩力学性质的影响，特别是在定义针对特定压裂区间的机械地层学方面的影响，仍然很少被探讨。在这项研究中，评估了沉积环境对拉杰马哈尔盆地页岩样品力学性质的影响。通过巴西劈裂拉伸强度测量样品的拉伸强度，并计算脆性指数作为机械性能的量度。此外，还进行了电感耦合等离子体发射光谱 (ICP-OES)、X 射线荧光光谱 (XRF)、Rock-Eval 6 和 X 射线衍射 (XRD) 分析，以评估来自不同地区的样品的地球化学特征。观点。结果表明，这种通常由沉积环境控制的地球化学变化会影响样品的机械性能。根据主量和微量元素指标，确定沉积环境为被动大陆边缘，具有湿热的古气候条件和淡水缺氧环境。观察到页岩样品的拉伸强度和脆性指数分别在 0.93 至 4.12 MPa 和 0.71 至 3.40 之间变化，而 TOC 超过 15 wt% 的样品与拉伸强度具有很强的负相关性，正如合理预期的那样，由于强度减弱沉积有机质对页岩基质的影响。拉伸强度和脆性指数与粘土矿物含量（特别是其类型）呈正相关，但与石英含量呈负相关。此外，与含有成岩二氧化硅的样品相比，富含生物二氧化硅的样品表现出较低的脆性。然而，机械性能随埋深的变化并不显着，并且应力-应变曲线的检查表明了样品取回层的总体脆性性质。总体而言，要在拉杰马哈尔盆地研究部分的机械地层学方面获得更可靠的结论，需要额外的垂直采样。