FACIES PARTITIONING AT REGIONAL AND FIELD SCALES IN THE BARREMIAN KHARAIB-2 CARBONATES, UAE

IF 1.8 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY
Pierre Gatel, Jean Borgomano, Jeroen Kenter, Tarek Mecheri
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引用次数: 0

Abstract

Carbonates in the Lower Cretaceous (Barremian to early Aptian) Kharaib Formation are reservoir rocks at giant oil fields in the UAE and Qatar. The Barremian Kharaib-2 member (K60), the focus of this study, is in general composed of a regionally continuous succession of high-energy, shallow-water limestones bounded above and below by “dense” low-energy mud-rich strata. Despite several decades of research, conventional carbonate facies classification schemes and resulting facies groupings for the Kharaib-2 member have failed to show a statistically acceptable correlation with core- and log-derived petrophysical data. Moreover, sedimentary bodies potentially responsible for dynamic reservoir heterogeneities have not clearly been identified. This paper proposes a standardized facies classification scheme for the Kharaib-2 carbonates based on vertical facies proportion curves (VPCs) and variogram analyses of core data to construct stratigraphic correlations at both field and regional scales. Data came from 295 cored wells penetrating the Kharaib-2 member at ten fields in the on- and offshore UAE. Thin, dense intervals separating reservoir units were adopted as fourth-order transgressive units and were used for stratigraphic correlation. Field-scale probability maps were used to identify sedimentary bodies such as shallow-water rudistid shoals.

Regional stratigraphic correlations of the Kharaib-2 member carbonates based on the VPCs identified variations in depositional environments, especially for the lower part of the reservoir unit; depositional facies at fields in the SE of the UAE were interpreted to be more distal compared to those at offshore fields to the NW. At a field scale, the VPCs failed to identify significant lateral variations in the carbonates. However, variogram analyses of cored wells showed spatial concentrations of specific facies in the inner ramp domain which could be correlated with high-energy depositional bodies such as shoals dominated by rudist debris. The bodies were sinusoidal in plan view with lengths of up to 8 km and widths of ca. 1 km. Although similar-shaped bodies with these dimensions have been reported from other carbonate depositional systems, they have not previously been reported in the Kharaib Formation. At a regional (inter-field) scale, the stratigraphic correlation of standardized sedimentary facies remains problematic; however, mapping of facies associations and their relative proportions relative to their environments of deposition demonstrated new patterns for the stratigraphic architecture of the Kharaib-2 member in the UAE.

阿联酋巴里米亚海盆Kharaib-2碳酸盐岩在区域和实地尺度上的岩相分区
下白垩统(巴里米统至早安普统)Kharaib 组碳酸盐岩是阿联酋和卡塔尔巨型油田的储油层岩石。本研究的重点--巴里米亚系 Kharaib-2 组(K60),总体上由区域连续的高能浅水灰岩演替组成,其上下部以 "致密 "的低能富泥质地层为界。尽管经过数十年的研究,传统的碳酸盐岩岩相分类方案以及由此产生的 Kharaib-2 成员岩相分组与岩心和测井获得的岩石物理数据之间并没有显示出统计学上可接受的相关性。此外,可能造成储层动态异质性的沉积体也没有得到明确识别。本文根据岩心数据的垂直岩相比例曲线(VPCs)和变异图分析,提出了一套针对 Kharaib-2 碳酸盐岩的标准化岩相分类方案,以构建油田和区域尺度的地层相关性。数据来自阿联酋陆上和近海十个油田的 295 口穿透 Kharaib-2 碳酸盐岩的岩心井。将分隔储层单元的细密间隔作为四阶递变单元,用于地层关联。根据 VPCs 对 Kharaib-2 碳酸盐岩进行的区域地层关联确定了沉积环境的变化,尤其是储层单元下部;与西北部近海油田的沉积面相比,阿联酋东南部油田的沉积面被解释为更远。在油田范围内,VPCs 未能确定碳酸盐岩的显著横向变化。然而,对取心油井的变异图分析表明,在斜坡域内部存在特定岩相的空间集中,这些岩相可与高能沉积体(如以芦苇碎屑为主的浅滩)相关联。这些沉积体从平面上看呈正弦曲线,长度可达 8 千米,宽度约为 1 千米。虽然在其他碳酸盐沉积系统中也曾发现过类似形状的岩体,但在哈赖卜地层中还没有发现过。在区域(油田间)范围内,标准化沉积面的地层关联仍然存在问题;然而,绘制面的关联及其相对于沉积环境的相对比例,为阿联酋 Kharaib-2 成员的地层结构展示了新的模式。
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来源期刊
Journal of Petroleum Geology
Journal of Petroleum Geology 地学-地球科学综合
CiteScore
3.40
自引率
11.10%
发文量
22
审稿时长
6 months
期刊介绍: Journal of Petroleum Geology is a quarterly journal devoted to the geology of oil and natural gas. Editorial preference is given to original papers on oilfield regions of the world outside North America and on topics of general application in petroleum exploration and development operations, including geochemical and geophysical studies, basin modelling and reservoir evaluation.
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