The effect of oil extraction on porosity and methane adsorption for dry and moisture-equilibrated shales
The effect of oil extraction on porosity and methane adsorption for dry and moisture-equilibrated shales
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DOI：
10.1016/j.fuel.2022.123304
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发表时间：
2022
期刊：
影响因子：
7.4
通讯作者：
Wei Li;Lee Stevens;W. Meredith;C. Uguna;C. Vane;Bo Zhang;A. Carr;D. Zheng;C. Snape
中科院分区：
文献类型：
--
作者：
Wei Li;Lee Stevens;W. Meredith;C. Uguna;C. Vane;Bo Zhang;A. Carr;D. Zheng;C. Snape
用于估算天然气储量（GIP）的页岩孔隙度和甲烷吸附能力受孔隙结构中的水分和油以及成熟过程中天然存在的油（包括用于钻井的污染钻井泥浆液）的影响。为了证明可提取油对干和湿平衡页岩的甲烷吸附能力的影响，研究了来自中国的两个过成熟页岩（SH 1，SH 2）和来自英国的两个较低成熟页岩（BS 3，GH4）。从过成熟页岩（<0.5wt%TOC）中提取的油的产率低，并且来自油基钻井泥浆，而从较低成熟度的UK页岩（1.1- 2.5wt%TOC）中提取的高得多的产率主要来自成熟产生的油。在提取之后，对于干燥的过成熟页岩，观察到总纳米孔体积（<100 nm）的最小变化（<5%），但是对于干燥的较低成熟页岩，观察到显著增加（95%和176%）。60%以上的抽出油存在于微孔和中孔中，去除可以疏通堵塞的孔道，扩大可进入的中孔和大孔体积。提取的页岩的含水量较低，观察到减少7-37%。甲烷平衡吸附容量增加后，石油开采的干和湿页岩，特别是较低成熟度的页岩，其中增加超过200%的湿页岩。亨利定律用于表明干页岩的油中不存在显著量的溶解甲烷。在确定孔隙度和甲烷吸附能力之前，从页岩中提取石油可能导致水分平衡页岩的GIP被高估，特别是对于油窗页岩，其中本研究中研究的页岩被高估了22%。这些研究结果提供了一个更好的理解的残余油和水的GIP的综合影响，并避免其高估。
The porosity and methane adsorption capacity of shale used to estimate gas in place (GIP) are affected both by moisture and oil residing in the pore structure, as well as oil naturally present from maturation, which can include contaminant drilling mud fluids used for drilling. To demonstrate the impact of extractable oil on methane adsorption capacity for both dry and moisture-equilibrated shales, two overmature shales from China (SH1, SH2) and two lower mature shales from UK (BS3, GH4) have been investigated. The oils extracted from the overmature shales (<0.5 wt% TOC) are in low yield and arise from oil-based drilling mud, while the much higher yields from the lower maturity UK shales (1.1–2.5 wt% TOC) is mainly from oil generated by maturation. After extraction, minimal changes (<5%) in total nanopore volume (<100 nm) were observed for the dry over mature shales, but significant increases (95 and 176%) were observed for the dry lower maturity shales. More than 60% of the extracted oil resides in micro and mesopores, and removal could unblock the micropore necks and enlarge the accessible meso and macropore volume. Moisture contents are lower for extracted shales, with reductions of 7–37% observed. Methane equilibrium adsorption capacities increased after oil extraction for both the dry and wet shales, especially for lower maturity shales, where increases were over 200% for the wet shales. Henry’s Law was used to show that there were not significant amounts of dissolved methane in oils for the dry shales. Extracting oil from shales prior to determining the porosity and methane adsorption capacity can lead to the GIP being over-estimated for moisture equilibrated shales, particularly for oil-window shales where an overestimation of 22% was obtained for the shale investigated in this study. These findings provide a better understanding of the combined impacts of residual oil and water on GIP and avoid its overestimation.