Carbonate Reservoirs - Sedimentology, Diagenesis and Reservoir Quality Evaluation

Course Description

An understanding of the depositional origin, together with the post-depositional modifications, is imperative to the successful exploration and production of carbonate sediments, which hold more than 60% of the world’s oil and 40% of the world’s gas reserves. Although carbonate rocks present complexity, this course is designed to understand the basic principles of carbonate sedimentology, diagenesis and reservoir characterization while making it straightforward to grasp and integrate the information.

The first part of this course is designed to develop skills in characterizing carbonate rocks and identifying and interpreting their depositional settings. This includes an insight into the controls on the carbonate factory (such as environmental, biological, physical, chemical and climatic controls), an in-depth examination of the classification of carbonate textures and gives an understanding of the larger scale tectonic setting and depositional geometry of carbonate platforms. The principles of sequence stratigraphy and its importance in the subsurface characterization of carbonate reservoirs will also be discussed. All these factors are crucial in predicting the geometry of carbonate reservoirs in the subsurface and developing accurate depositional models, which in turn will have an impact on the prediction of the reservoir architecture.

The second session of the course will focus on the diagenetic processes and products that have an impact on carbonate reservoirs. This will encompass the identification of the products and processes involved within meteoric, marine and burial diagenetic environments, using both petrographical and geochemical analytical techniques, while taking into consideration their implications on the resultant reservoir properties. In addition to this, the process of dolomitisation and the proposed models of dolomite formation (including expected body geometries) will be discussed, illustrating whether this process benefits or hinders reservoir quality. This section will also review the various analytical techniques utilised in identifying the origin of the diagenetic phases and thereby aiding the prediction of their potential vertical and lateral extent.

The third and final part of the course will analyse the pore system evolution, integrating the intricate link between sedimentology and diagenesis to aid prediction of reservoir properties at the field scale. The classification of pore types will be discussed, with their primary depositional or secondary diagenetic origin being determined in order to understand their spatial relationships relative to the sedimentological framework and hence their potential connectivity. The characterization of micrite textures will also be discussed to illustrate their impact on microporosity, an important factor to consider when characterizing unconventional tight reservoirs. This course outlines how to conceptually build a reservoir architecture model by integrating the key controls on reservoir quality within the sedimentological framework, which in turn can be used to assess and predict the lateral and vertical variations in porosity and permeability at the large scale.

This course will be accompanied by a series of in-class exercises, which will emphasize the integration of the various datasets, providing participants with experience in carbonate reservoir characterization.

Course Objectives

Upon completion of the course, participants will be able to:

• Understand a carbonate system, including the major controls on carbonate production, describe carbonate sediments and their associated heterogeneity, and understand the techniques used to apply a sequence stratigraphic framework in a typical carbonate succession;
• Understand the various diagenetic processes that carbonate sediments are predisposed to and how to identify the origin of resultant products and hence their impact on reservoir quality. Knowledge on the analytical techniques used to characterize diagenetic products will also be gained;
• Determine how sedimentological parameters and diagenetic process impact reservoir quality in order to aid prediction at the field scale.

Course Outline

Sedimentology and sequence stratigraphy - Days 1-2

Part A: The carbonate system - “Carbonates are born not made”

• Mineralogy, composition and classification of carbonate rocks;
• The carbonate factory and controls on carbonate production;
• Applied carbonate facies analysis with core-based and thin-section examples;
• The key to identifying carbonate depositional environments.

Part B: Sequence stratigraphy applied to carbonate reservoirs

• Introduction to the basic concepts of sequence stratigraphy;
• The carbonate record and sea level variations;
• How to establish a sequence stratigraphic framework;
• Prediction of the sedimentological heterogeneity and interpretation of the sedimentological architecture.

Diagenesis - Day 3

Part A: The diagenetic realm

Introduction to diagenetic processes;

• Diagenetic environments;
• Dolomites and evaporites;
• Building a paragenetic sequence.

Part B: Analytical techniques

• Advanced microscopy analyses including cathodoluminescence and scanning electron microscopy;
• Geochemical analyses such as trace elements, stable isotopes and fluid inclusion thermometry.

Reservoir quality assessment - Days 4-5

Part A: Reservoir quality analysis - what it is and how to approach it

• Definition of reservoir quality;
• How to characterize reservoirs.

Part B: Pore types and connectivity

• Concepts and definitions;
• The carbonate pore type classification(s);
• Permeability and pore-throat radius distributions;
• Manipulating reservoir quality data.

Participants’ Profile

The course is targeted at all geoscientists, including petroleum geologists, petrophysicists and petroleum engineers involved in exploration and production of carbonate plays.

Prerequisites

Although previous knowledge on carbonate sedimentology is not necessarily required, participants should have some knowledge of geology.

About the Instructor

Laura Galluccio (Ph.D.) is one of Badley Ashton’s UK-based senior carbonate reservoir geologists with an interest in carbonate petrography and sedimentology. She specialises in sedimentology, diagenesis and reservoir quality characterization of limestones and dolomites in both conventional and unconventional reservoirs. She has wide experience in the Middle East, the USA, Europe and Africa. The projects she has been involved in cover a wide range of depositional environments from shallow to deeper water carbonates. Laura received his BSc, MSc and PhD at the University of Naples (Italy), with her PhD conducted in conjunction with Shell Italy. As an effective communicator and with a proven track record of excellent client care, past roles include Team Leader of the Carbonate Group, and local Business Manager and Consultant Geologist based in PDO’s offices, Muscat. Since her appointment as Regional Manager in August 2017, Laura oversees business activity in the Middle East, Africa and Asia, supported by regional Operations and Portfolio Managers. Laura’s other research interests include sedimentology and sequence stratigraphy of ancient and recent carbonate platforms and the characterization of diagenetic processes affecting carbonate sediments with integration into the regional framework and influence on the pore system. She is currently involved in research on the diagenesis and pore volume assessment of Hyamm Formation in Oman in collaboration with the Ferrara University and Sultan Qaboos University, as well as a project focused on the role of hydrocarbons emplacement for calcite precipitation, in collaboration with Newcastle University. Laura has undertaken teaching of geological mapping, petroleum geology and reservoir quality evaluation at both BSc and MSc levels, while co-supervising a variety of BSc and MSc carbonate research projects.

Catherine Breislin (Ph.D) is a Reservoir Geologist working in Badley Ashton’s UK-based Carbonate Team. She specialises in carbonate sedimentology, diagenesis and reservoir quality analysis using a range of techniques in both conventional and unconventional reservoirs. Her work to date has focused on investigating the controls of depositional facies, platform architecture, and structural development on basin-scale diagenetic fluid flow and its impact on reservoir quality. Her project work has covered a wide range of depositional environments from shallow to deeper water carbonates.

Catherine received her MESci at the University of Liverpool (UK), and PhD at the University of Manchester (UK), with her PhD conducted in conjunction with Shell and the British Geological Survey. Catherine has a strong background in field geology, core-logging, carbonate sedimentology and geochemistry, and is proficient in conducting spatial integration of multiple data sets. She also has experience in lab-based mineral identification analyses, where she has developed best practice methodologies and workflows. While co-supervising an MSc carbonate research project at Manchester University, Catherine has undertaken teaching of carbonate sedimentology, geological mapping, petroleum geology and reservoir quality evaluation at both BSc and MSc levels.