关键词: 二维核磁共振, 流体赋存, 源-储耦合, 陆相页岩, 复兴地区, 四川盆地

Abstract:

The proved shale oil and gas initially-in-place （PIIP） in the Fuxing oilfield have been successfully booked， confirming the great resource potential of continental shale oil and gas in the Fuxing area， Sichuan Basin. Although substantial studies have been conducted， several bottlenecks persist in research on continental shales in this area， including distorted resource evaluation results caused by the failure to restore the original oil-water composition， a lack of methods for whole-fluid quantitative characterization， and an unclear understanding of source rock-reservoir coupling mechanisms. To address these challenges， we investigate the Middle-Lower Jurassic organic-rich continental shales in the Fuxing area， eastern Sichuan Basin， with target intervals including the lower sub-member of the 2nd member of the Lianggaoshan Formation （Liang 2 Member）， as well as the 1st sub-member of the Dongyuemiao Member （Dong 1 Sub-member） and the 2nd sub-member of the Da'anzhai Member （Da 2 Sub-member） of the Ziliujing Formation. A scheme for lithofacies classification based on four parameters （i.e.， color， organic matter abundance， sedimentary structure， and mineral composition of rocks） is established， enabling the identification of eight major shale lithofacies in the study area. The fluid occurrence patterns and source rock-reservoir coupling characteristics of various shale lithofacies are systematically investigated in this study. Based on the 2D T₁-T₂ nuclear magnetic resonance （NMR） chart for the quantitative identification of major hydrogen-bearing components in the Middle-Lower Jurassic shales in the Fuxing area， a workflow is developed for fluid restoration and the evaluation of fluid occurrence characteristics across various shale lithofacies. The in-situ fluid saturation and distribution in reservoirs are restored through drainage and imbibition experiments. Accordingly， the source rock-reservoir coupling characteristics of shales at the target intervals are comprehensively evaluated based on the source rock-reservoir coupling coefficient （SRCC） for continental shales. The results indicate that the occurrence state of shale oil is jointly controlled by organic matter type， organic matter abundance， porosity， pore size distribution， and fluid composition， which serve as the key indicators for evaluating high-quality reservoirs. The contents of free and adsorbed oil， along with their ratios， are important parameters for characterizing the oil-bearing properties and oil mobility of shales. Clay-bound water occupies part of spaces for shale oil occurrence， while capillary-bound water tends to block pore-throat channels， both factors significantly restricting the reservoir properties and fluid mobility. Both the grayish-black carbon-rich silty laminar clayey shale facies （L1） in the lower sub-member of the Liang 2 Member and the grayish-black carbon-rich silty shelly laminar clayey shale facies （L7） in the Dong 1 Sub-member are identified as Class A lithofacies characterized by favorable source rock-reservoir coupling relationships. The evaluation results are highly consistent with the experimental data， successfully restoring the oil-bearing properties， reservoir properties， and fluid mobility of the reservoirs under geological conditions. The methodology established in this study， integrating lithofacies identification， fluid restoration， quantitative evaluation based on key parameters， and coupling classification and grading， is highly practical and reliable， yielding encouraging well test and pilot production results. Furthermore， this methodology enables the accurate calculation of key parameters such as total organic carbon （TOC） content， free and adsorbed hydrocarbon contents， total porosity， and bound water content. Therefore， it serves as an effective approach for selecting continental shale enrichment intervals and optimal landing zones， thereby providing strong support for the three-dimensional exploration and efficient exploitation of continental shale oil and gas in the Fuxing area.

Key words: 2D nuclear magnetic resonance （NMR）, fluid occurrence, source rock-reservoir coupling, continental shale, Fuxing area, Sichuan Basin