Geological and Geomechanical Characterization of a Permo-Triassic Carbonate Reservoir in Eastern Saudi Arabia

Geological and Geomechanical Characterization of a Permo-Triassic Carbonate Reservoir in Eastern Saudi Arabia. Masters thesis, King Fahd University of Petroleum and Minerals.

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Arabic Abstract

يعد متكون الخف من المكامن الرئيسية للغاز الطبيعي في المملكة العربية السعودية. و قد تم ترسيب طبقات الخف خلال أواخر العصر البرمي و بدايات العصر الترياسي ، و ويتراوح سمكه ما بين 1600 و 2200 قدما تتكون من الحجر الجيري وحجر الدولوميت في المنطقة التي تمت فيها دراسة ذا البحث وبالإعتماد على خمسة آبار. ركز هذا البحث على الخصائص الجيولوجية ومنها المسامية وبحث علاقتها بعدد من الخصائص الجيوميكانيكية لمتكون الخف. أيضا، تم بناء ثلاثة نماذج جيوميكانيكية أحادية البعد لمحاكاة الخصائص الجيوميكانيكية لمتكون الخف والتي ستساعد على تطوير الحقول في المستقبل.

English Abstract

The Permo-Triassic Khuff Formation is a major reservoir in Saudi Arabia. The thickness ranges between 1600 and 2200 ft consisting of mainly limestone and dolostone lithologies in the vicinity of the study area. The Khuff is divided into four informal subsurface members, starting from top A, B, C and D. The geomechanical properties of the Khuff Formation were never studied in this present area and scarce published work is available from either nearby areas or regional studies. Deducing geomechanical properties allows building calibrated 1D mechanical earth models (MEM) that can help predicting the in-situ stress conditions. Moreover, knowledge of stress condition magnitude and direction is a key to predict whether the natural fractures are stable under given stress conditions. This study aims to characterize the natural fractures, deduce the geomechanical properties and in-situ stress conditions in the Khuff A, B, and C. A comprehensive subsurface dataset is utilized to achieve the objective of this work. The dataset includes borehole resistivity image logs, borehole acoustic image logs and wireline formation evaluation logs. It also includes core which provided samples for the triaxial testing, conventional core analysis, thin sections petrography and XRD analysis. Properties such as confined compressive strength, Young’s modulus, Poisson’s ratio, cohesion, friction angle, porosity, and mineralogy were utilized for regression analysis and building 1D MEM. Major mineralogical constituents are calcite, dolomite, and anhydrite. Moreover, these lithologies have porosity ranging between 0.6% and 29.1%. Porosity was found to increase exponentially with increasing dolomite content when anhydrite is not present. Bedding-parallel stylolites were more common in the limestone and dolomitic limestone lithologies. Core intervals with high stylolite density are associated with elevated gamma ray readings in both Khuff A and Khuff B. However, the Khuff C does not show the same relation. No faults or major natural open fractures were identified on borehole resistivity images. The majority of natural fractures observed in cores are mineralized Mode-I fractures and are associated with bedding-parallel stylolites. Shear natural fractures were limited to hydrothermal dolomite beds present in the Khuff C of Well-A. From cross-cutting relationships in core, vertical stylolites developed after hydrothermal dolomitization. Moreover, bedding-parallel stylolites formed before the hydrothermal dolomitization and continued to form thereafter. Lithology is the main control on brittleness in the Khuff Formation. A new scheme of mechanical layering has been developed where the Khuff A, Khuff B, and Khuff C are divided into ten mechanical layers. Young’s modulus, unconfined compressive strength, cohesion, and friction angle are primarily controlled by porosity in the Khuff Formation. In-situ stress conditions were predicted through 1-D models of the Khuff Formation and these models helped to estimate average gradients of σ_Hmax , σ_hmin and σ_V which are 1.31 psi/ft, 1.085 psi/ft and 0.89 psi/ft, respectively. No natural fractures are under critically-stressed state in the Khuff Formation as per the predicted in-situ stress conditions.

Item Type: Thesis (Masters)
Subjects: Earth Sciences
Department: College of Petroleum Engineering and Geosciences > Geosciences
Committee Advisor: Hariri, Mustafa
Committee Members: Korvin, Gabor and Belayneh, Mandefro and Abdullatif, Osman
Depositing User: ALGHANNAM SALEH (g201003540)
Date Deposited: 13 Jun 2016 07:14
Last Modified: 01 Nov 2019 16:34