DataSheet1_Effect of Hydrocarbon Presence and Properties on the Magnetic Signature of the Reservoir Sediments of the Catcher Area Development Region, UK North Sea.docx

This paper presents a detailed study investigating the effect of hydrocarbon presence on magnetic mineral diagenesis in sediments from the Catcher Area Development (CAD) region, UK North Sea, between 1,000 and 1,500 m (True Vertical Depth Sub-Sea). Magnetic analysis of core samples from hydrocarbon fields of the region and nearby dry-well sandstones (background) was carried out to determine if their signatures can serve as a proxy for understanding petroleum reservoir systems. From the background samples, nanometric and micron-sized magnetite, hematite and titano-iron oxides, were identified. Hydrocarbon presence in the reservoir sediments was found to diminish the iron-oxide signature and favour the precipitation of hexagonal pyrrhotite, siderite and potentially vivianite, lepidocrocite, greigite and paramagnetic iron sulphides. Hexagonal pyrrhotite was found at the oil-water transition zones. This relationship is possibly related to biodegradation at this interface. Siderite was found in increased abundance at shallower depths within the reservoir, which we attribute to hydrocarbon vertical migration and biodegradation. The interbedded shales also experienced significant magnetic mineral diagenesis that depended on its proximity to the hydrocarbon plume. These findings suggest that mineral magnetism can be applied to the identification of oil-water transition zones, reserve estimation, production planning and the determination of hydrocarbon migration pathways. It also suggests that mineral magnetic methods can be used to estimate the timing of hydrocarbon migration.

本文针对英国北海Catcher油田开发（Catcher Area Development, CAD）区域水下真实垂深（True Vertical Depth Sub-Sea）1000~1500米处的沉积物，开展了烃类（hydrocarbon）赋存对磁性矿物成岩作用影响的详细研究。本研究对该区域烃类油田的岩心样品及邻近干井砂岩（背景样品）开展磁性分析，以探究其磁信号能否作为表征石油储层系统的替代指标。从背景样品中，研究人员鉴定出纳米级、微米级磁铁矿（magnetite）、赤铁矿（hematite）及钛铁氧化物（titano-iron oxides）。研究发现，储层沉积物中的烃类赋存会削弱铁氧化物的磁信号，并促进六方磁黄铁矿（hexagonal pyrrhotite）、菱铁矿（siderite）及潜在的蓝铁矿（vivianite）、纤铁矿（lepidocrocite）、胶黄铁矿（greigite）和顺磁性硫化铁（paramagnetic iron sulphides）的沉淀。研究在油水过渡带发现了六方磁黄铁矿，该现象或与该界面处的生物降解作用相关。储层较浅深度处的菱铁矿丰度显著升高，我们将其归因于烃类垂向运移及生物降解作用。夹层页岩同样发生了显著的磁性矿物成岩作用，其作用程度取决于与烃类羽状流的相对距离。上述研究结果表明，矿物磁性可用于识别油水过渡带、估算储量、制定生产规划及确定烃类运移路径；同时，矿物磁性方法亦可用于估算烃类运移的时间节点。