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在北海北部,中侏罗统布伦特(Brent)群阿连阶的Oseberg组(0m～80m厚)是一个重要的储集单元,它由多套砂质吉尔伯特型三角洲组成。在自然伽马测井曲线上识别出的小规模(1.5m～10.0m)向上变细的单元对应于单个三角洲沉积层系,正如在倾角测井曲线上倾角向上变陡的趋势所证实的那样。在每一套三角洲沉积作中,较陡的前积斜坡通常表现为薄层状砂岩相(崩塌颗粒流沉积),而前积斜坡下部、趾积层和底积层大多由块状砂岩相(砂质碎屑流沉积)组成。从中等规模(可达40m)上看,在叠置的三角洲沉积层系中,自然伽马测井曲线表现出向上变细和向上变粗两种趋势,这两种趋势在井间可以追踪,分别解释为相对海平面减速上升和加速上升。砂质碎屑流沉积相对富集表明三角洲前积斜坡上部的沉积是周期性的,而且具有明显的不稳定性,该沉积可能是在三角洲前部水体变深时形成的。然而,正常的单个吉尔伯特型三角洲沉积层系的前积层可能是在水深变化小或无变化期间沿近水平地形沉积的。产生目前所观察到的垂向叠置的三角洲沉积层系的长期变化是相对海平面的总体上升。用阶梯状样式模拟海平面上升可以对顶积层稀少作出解释。在Horda台地上,Oseberg组向东逐渐削切下伏的Drake组,表明在Ose-berg三角洲发育之前存在构造抬升和低水位海平面。因此,Oseberg组被看作为发育于沉积物供应速率相对较高且海平面变速上升期间(上覆的Rannoch组底面可见阿连期末海泛作用达到顶峰)沉积的低水位进积楔。倾角测井资料与岩心和其它测井资料相结合是解释储层内部构造的关键。斜坡校正模式预测,Oseberg型叠置块状砂岩储层将优先存在于快速沉降或同沉积断裂作用区,或出现于已有的断层陡坎背流处的深水区。
In the northern part of the North Sea, the Oseberg Formation (0m ~ 80m thick) in the Middle Jurassic Brent Formation of the Middle Jurassic is an important reservoir unit consisting of multiple sets of sandy Gilbert delta. The small-scale (1.5m ~ 10.0m) up-downed cells identified on the gamma ray logging curve correspond to a single delta sedimentary system, as evidenced by the tendency of the dip angle to steer upward on the dip log . In each set of delta sediments, the steeper foreshortends usually show thin-bedded sandstone facies (sediment flow deposition), while the lower part of the fore slope, toe and bottom sediments mostly consist of massive sandstone facies Sandy debris flow deposition). From the medium scale (up to 40m), the natural gamma ray logging curves show upward and downward thickening trends in the superimposed Delta sedimentary system. Both of these trends can be traced between wells, Respectively, as the relative sea level slowed down and accelerated up. The relative enrichment of sandy debris flow shows that the sediments in the upper part of the delta front are periodic and have obvious instability, which may be formed when the water in the front of the delta becomes deeper. However, the pre-buildup of a normal single Gilbert delta sedimentary system may be deposited along near horizontal terrain with little or no change in depth. The long-term changes that produce the vertically-superimposed Delta sedimentary facies currently observed are the overall rise in relative sea level. Modeling the sea level rise in a staircase style can explain the sparse top layer. On the Horda platform, the Oseberg group plunges eastward into the underlying Drake Formation, indicating that there was tectonic uplift and low-water sea level before the Ose-berg delta developed. Therefore, the Oseberg Formation is considered to be a low-water-level wedge that developed during the relatively high sediment supply rates and the sea-level rise and fall (the bottom of the overlying Rannoch Formation shows the onset of sea level apex). The combination of dip logs and cores and other well logs is the key to explaining the internal structure of the reservoir. The slope correction model predicts that the Oseberg-type superimposed massive sandstone reservoirs will preferentially exist in areas of rapid subsidence or syndepositional fractures or in deepwater areas existing at the dips of the existing fault scarps.