Dolomite Reservoir Architecture and Pool Characterization of Ordovician Midale Field
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摘要: 综合三维地震、钻井、岩心和薄片资料分析了该油藏的储层展布格架、油藏构造及演化、油藏类型和控制因素等。在钻井剖面对比图上依据密度和中子测井,将白云岩储层可划分为4个小层。第1、2小层由于位于圈闭构造的较高部位因而通常含油。第3、4小层可能由于在某处与第1、2小层连通,虽然也具低幅度构造和更大的厚度及孔隙度,但多为水层;又因其容易侧向尖灭,故有可能形成地层圈闭。三维地震解释和正演模型均表明,当第1、2小层较厚时,常对应于强振幅和高频反射;当第3、4小层较厚且4个小层并存时会在原储层反射位置下方多出一个波峰同相轴,而且第3、4小层的尖灭通常伴随着该同相轴的终止。这一点有助于寻找与第3、4小层上倾尖灭有关的圈闭。Midale油藏的空间分布受局部低幅度构造和储层小层发育状况的双重控制。油藏驱动机制可能为边水和底水两种类型的结合。根据地震剖面上的地层关系和由三维地震资料所做的古构造演化图来看,油藏低幅度构造的形成与后期地层在前寒武基岩古隆起上的披覆及该隆起在后期多次不整合发生期间的重新活动有关。圈闭雏形形成于早志留到中泥盆世,最终定型于晚白垩世。区域构造演化和油气运移研究表明,有利的油气聚集带位于某些靠近油源区的古鼻隆的东北翼。Abstract: The Upper Ordovician Midale Field is located in the northern Williston Basinin southeastern Saskatchewan, Canada.It consists of a serious of low-relief structural traps. The oil source rocks are the same or older stratigraphy in the southern basin center. Thereservoirs are characterized by intercrystalline porosity in the dolomitized matrix with variable amount of vugs and fractures. Based on core examination and density and neutron log analysis, the carbonate reservoirs in the Red River Yeomen Formation can be divided into four zones.Zones1 and 2 are situatedin the upper part of the structural traps and usually bear oil. Although zones3 and 4 are thicker with higher porosity, they usually contain water only because they are located below the spill point of hydrocarbon traps.On a regional scale, however, zone 3 and 4 could be the attractive targets for the future exploration of possible stratigraphictraps where these zones pinch-outlaterally. Thickerzone 1 and 2 are characterized by high-amplitudeandhigh-frequency reflections on seismic profilesbased on examination of log cross-sections, their correspondingwell-linked 3 D seismic profiles,and forward modeling of seismic response. Zone3 and 4, where all four zones are present, can be identified by an additionalpeak beneath the original reservoir reflectionon seismic profiles. The terminationof this additional peak on a seismic profile is, therefore, an indication of pinchout of reservoir zone 3 and 4.This can be used to identify possible stratigraphic traps. The Ordovician oil pools of the Midale area are spatially associated with localized low-relief structuresand presence of the reservoirs zones.The driving mechanism for the Midale pools is interpreted to be a combination ofedge water and bottom waterdrive systems.Based on our analyses of 3D seismic dataand their implication on the stratigraphic and structural evolution in the region, these low relief structures are interpreted as the drape of Red Riverstrata over local Precambrianbasement highs that could have reactivated later. The traps were initiated during the Middle Silurian to the Early Devoniantime and finalized during the Late Cretaceous. Future explorationtargets of stratigraphic trap play are identifiedon thenortheastern wings of the nose structure that is close tohydrocarbon sources.
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Key words:
- dolomite reservoir /
- zone correlation /
- reservoir prediction /
- low-relief structure /
- pool type
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