Assessment of microfacies and diagenesis in a carbonate reservoir using thin section petrography and XRD mineralogy.

Project Abstract

This study investigates the microfacies architecture and diagenetic evolution of a carbonate reservoir to elucidate how depositional textures and post-depositional alterations govern reservoir quality and heterogeneity. A multi-scale approach integrates thin section petrography, scanning electron microscopy (SEM), cathodoluminescence (CL), and X-ray diffraction (XRD) mineralogy to characterize primary textures, constituent minerals, cementation patterns, pore-throat distributions, and diagenetic overprints. Field samples from a target carbonate formation were systematically collected across depth and lateral sections to capture lateral facies transitions and vertical diagenetic zoning. Petrographic analysis identifies major depositional textures (grain-supported packstones, wackestones, and mudstones), fossil components, and allochemical vs orthochemical assemblages, enabling the reconstruction of paleoenvironmental conditions and depositional energy regimes. SEM and CL examinations reveal microstructural features such as?ferroan, mosaic cement, syntaxial overgrowths, solution-enhanced pores, microcrystalline precipitates, stylolites, and dolomitization textures, allowing precise discrimination between diagenetic stages. XRD mineralogical data quantify the relative abundances of key carbonate polymorphs (calcite, dolomite), clays, quartz, feldspars, and minor minerals, providing insight into diagenetic drivers such as dolomitization, diagenetic cementation, and meteoric or burial alteration. Integrating petrographic and mineralogical results with porosity-permeability measurements obtained from core plugs and NMR-based pore-size distributions enables a robust petrographic-geo-mechanical model of reservoir quality. The research quantitatively assesses porosity types (primary intergranular, dissolution-enhanced, dolomitized, and moldic) and their stability under compaction and cement precipitation scenarios. Geostatistical analyses map facies distribution, diagenetic facies, and permeability anisotropy, highlighting zones of high-quality reservoir rock controlled by diagenetic enhancement (dissolution porosity and dolomitization) versus deterioration (cement fill and compaction). A diagenetic sequence is established to interpret the chronological order of events early marine cementation, meteoric dissolution, dolomitization, and burial cementation, followed by secondary porosity development in karst-like features. The study develops a predictive framework linking microfacies and diagenetic pathways to reservoir performance, enabling improved static and dynamic reservoir models. Sensitivity analyses explore how variations in mineralogy and pore geometry influence fluid flow under different production strategies, while uncertainty assessment addresses sampling limitations and diagenetic overprint variability. The outcomes provide actionable insights for reservoir characterization, including targeted well placement, stimulation planning, and enhanced oil recovery optimization by exploiting dissolution porosity and dolomite-rich intervals. By offering a reproducible methodology that combines thin-section petrography, SEM-CL, and XRD mineralogy with porosity-permeability correlations, this work contributes to more accurate reservoir quality assessment in carbonate systems and informs exploration strategies in analogous fields.

Project Overview

What This Project Is About

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A plain-language overview of studying rocks from a carbonate reservoir to understand tiny features and how rocks changed over time, using two simple tools: looking at thin slices of rock under a microscope and identifying minerals with a mineral-detecting method.

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The Problem It Addresses

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Carbonate rocks can store and leak fluids in different ways. Without knowing micro-scale features and diagenetic changes (how rocks were altered after formation), predicting reservoir quality is hard. This project helps bridge that gap by linking rock texture to its ability to hold and transmit fluids.

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Objectives of the Project

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1. Describe the tiny textures of carbonate rocks using thin-section images.
2. Identify minerals present with a simple X-ray method.
3. Explain how post-formation changes affect rock properties.
4. Correlate textures with porosity and permeability indicators.
5. Provide practical recommendations for evaluating reservoir quality.

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What You Will Do Step by Step

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1. Collect rock samples from a carbonate reservoir study unit.
2. Prepare thin sections and examine under a petrographic microscope.
3. Perform XRD analysis to identify major minerals.
4. Document microfacies types and diagenetic features (cementation, dissolution, compaction).
5. Link textures to porosity indicators from available data.
6. Interpret how diagenesis has altered reservoir performance.
7. Summarize findings and discuss implications for reservoir management.

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Expected Outcome

A clear, user-friendly report showing how micro-scale rock features and diagenetic changes influence reservoir quality, with actionable insights for exploration teams and engineers.