Data for: Natural Fracture System of the Cambro-Permian Wajid Group, Wadi Al-Dawasir, SW Saudi Arabia

This study investigates the regional and outcrop-scale fracture system within the Wajid Group exposures in Wadi Al-Dawasir, southwest Saudi Arabia. The Wajid Group is a Cambro-Permian siliciclastic succession that forms the main groundwater aquifers in the study area and is considered as a potential hydrocarbon reservoir in the Rub' Al-Khali Basin. The succession is composed of fluvial, marine, and glacial to glaciofluvial deposits. This study aims to characterize and model the fracture system within the Wajid Group in the Wadi Al-Dawasir area using satellite imagery and direct field measurements. A further study objective is to define the geological factors controlling the fracture distribution within the Wajid Group succession. Five sets of regional-scale fractures (lineaments) were defined: N000°, N015°, N035°, N075°, and N135°. In addition, five sets of the outcrop-scale fractures were delineated: N015°, N035°, N075°, N135°, and N165°. The N135°- and N035°-oriented fracture sets are predominant at the regional scale. At the outcrop scale, however, the N165°- and N075°-oriented fracture sets are predominant. The trace-length of the regional-scale fractures is distributed according to the negative exponential distribution. The fractures within the Wajid Group outcrops are vertical to sub-vertical extensional fractures (mode 1). Those fractures are open, however, and at some localities, they are sealed or coated with calcite or iron oxides. Fracture swarms with an orientation of N015° were also observed in the southeastern part of the study area. Hierarchical outcrop conceptual models of two fracture sets are proposed. The proposed models show that the regional-scale fractures are not influenced by stratigraphic or lithological variations. In contrast, the outcrop-scale fractures are controlled by the stratigraphic, lithological, and diagenetic variations in the fracture-hosting sandstone. The diagenetic characteristics (cementation and dissolution), bed thickness, and porosity of the fracture-hosting sandstone play a key role in the fracture distribution within the Wajid succession. The results of this study contribute to the understanding of groundwater flow behaviour within fractured aquifers in the study area and will help to enhance gas production from fractured hydrocarbon reservoirs in the Rub' Al-Khali Basin.

本研究针对沙特阿拉伯西南部达瓦西尔谷（Wadi Al-Dawasir）出露的瓦吉群（Wajid Group）内的区域尺度与露头尺度断裂系统展开调查。瓦吉群是一套寒武纪至二叠纪的硅质碎屑岩系（siliciclastic succession），构成研究区的主要地下水含水层（groundwater aquifer），同时被视为鲁卜哈利盆地（Rub' Al-Khali Basin）内的潜在油气储层。该岩系由河流相、海相以及冰川至冰水河相沉积物组成。本研究旨在利用卫星影像与实地直接测量数据，对达瓦西尔谷地区瓦吉群内的断裂系统进行表征与建模；另一项研究目标为明确控制瓦吉群岩系内断裂分布的地质因素。研究共识别出5组区域尺度断裂（线性构造，lineament），走向分别为N000°、N015°、N035°、N075°与N135°；此外还划分出5组露头尺度断裂，走向分别为N015°、N035°、N075°、N135°与N165°。区域尺度上，N135°与N035°走向的断裂组系占主导地位；而在露头尺度，占主导的则为N165°与N075°走向的断裂组系。区域尺度断裂的迹长服从负指数分布。瓦吉群露头内的断裂为垂直至近垂直的张性断裂（I型，mode 1），多数保持张开状态，但部分区域的断裂被方解石或氧化铁胶结或充填。研究区东南部还观测到走向为N015°的断裂群。本研究提出了两组断裂的分层露头概念模型，模型显示区域尺度断裂不受地层或岩性变化的影响；与之相反，露头尺度断裂受赋存断裂的砂岩的地层、岩性以及成岩作用变化控制。赋矿砂岩的成岩特征（胶结作用与溶蚀作用）、层厚以及孔隙度，对瓦吉群岩系内的断裂分布起到关键控制作用。本研究结果有助于理解研究区裂隙含水层内的地下水流动规律，同时将助力提升鲁卜哈利盆地内裂隙型油气储层的天然气产量。