Stratigraphic Trap Potential in the Lower Cretaceous Ratawi Interval, Partitioned Zone PZ, Saudi Arabia and Kuwait

I. Hakam, Niall Toomey, S. Ghose, J. Ponthier, Jeremy Zimmerman
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Abstract

The Lower Cretaceous Ratawi Oolite Formation is among the most prolific reservoirs in the PZ, having produced a significant amount of oil since the 1950's. The Ratawi is interpreted as a low angle carbonate ramp, with high-energy grainstone facies developing on structural highs. Production is focused on these structural highs, with very few well penetrations off structure. Recent work has identified potential Ratawi stratigraphic traps in prograding clinoforms along the flanks of the North Fuwaris structural high. Core data from Ratawi wells illustrate the interplay of depositional environment and diagenesis on reservoir quality. Gross depositional environment (GDE) maps created from the integration of seismic facies and core observations indicate the stratigraphic trap lies in the ramp slope. Reservoir quality variability of the ramp slope across the PZ is explained by the diagenetic history of the Ratawi. Early equant calcite cement develops from substantial meteoric runoff and lowers porosity, while later dissolution enhances reservoir quality. The area of interest is isolated from potential meteoric inputs; we do not expect equant calcite cement or the associated reduction in reservoir quality. Seismic interpretation was performed on recently acquired PZ 3D data to map the Ratawi section. Clinoforms (inclined geometry) were mapped along the western flank of the North Fuwaris high. These facies appear to have developed as a result of progradation to the NW and are indicative of good reservoir development. Leads were generated using the depth structure and GDE maps, supported by amplitude extraction and seismic inversion volumes. Amplitudes extracted from the clinoform shows that the strongest anomaly is along the structurally highest part of the horizon and the anomaly weakens downdip. High amplitudes could be a proxy for reservoir (porosity), and sharp turn-off in amplitude might indicate that lateral and updip facies changes to non-reservoir which is needed for an effective seal. Recent seismic inversion performed on the Ratawi interval shows a good match between the Acoustic Impedance (AI) from logs and the computed AI from the seismic. The Ratawi Oolite appears as a low impedance interval between overlying Ratawi Limestone and underlying Makhul. Porosity estimated from AI volumes appear to support possible Ratawi reservoir development along the flanks of North Fuwaris and Wafra highs.
沙特阿拉伯和科威特PZ分区下白垩统Ratawi段地层圈闭潜力
下白垩统Ratawi Oolite组是PZ最多产的储层之一,自20世纪50年代以来已经生产了大量的石油。Ratawi被解释为低角度碳酸盐斜坡,在构造高位发育高能颗粒岩相。生产主要集中在这些构造高点,很少有井穿出构造。最近的工作已经确定了沿北福瓦里斯构造隆起侧翼推进的斜形岩中潜在的Ratawi地层圈闭。Ratawi井的岩心资料说明了沉积环境和成岩作用对储层质量的相互作用。综合地震相和岩心观测绘制的总沉积环境(GDE)图表明,地层圈闭位于斜坡上。拉塔维组的成岩历史可以解释坡面斜坡储层物性的变化。早期等量方解石胶结物是由大量的大气径流形成的,降低了孔隙度,而后期的溶蚀则提高了储层的质量。感兴趣的地区与潜在的大气输入隔绝;我们不期望等量方解石胶结或相应的油藏质量降低。对最近获得的PZ 3D数据进行了地震解释,绘制了Ratawi剖面。斜形构造(倾斜几何形状)沿北福瓦里斯高地西侧绘制。这些相似乎是北西向沉积的结果,表明储层发育良好。在振幅提取和地震反演的支持下,利用深度结构和GDE图生成导联。斜仿岩振幅分析表明,在构造最高处异常最强,下倾异常减弱。高振幅可以作为储层(孔隙度)的代表,振幅的急剧关闭可能表明侧向和上倾相向非储层转变,这是有效密封所必需的。最近在Ratawi层段进行的地震反演表明,测井所得的声波阻抗(AI)与地震计算所得的AI吻合良好。Ratawi鲕粒岩表现为上覆Ratawi灰岩与下伏Makhul灰岩之间的低阻抗层。根据AI体积估算的孔隙度似乎支持沿北Fuwaris和Wafra高地两侧可能的Ratawi储层开发。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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