Atlas of Natural and Induced Fractures in Core

Fractured reservoirs are a significant part of the hydrocarbon production across the world, even though most were discovered to be fracture dominated after initial drilling. These fractured reservoirs are some of the largest and most productive oil and gas fields worldwide. Over the last three decades, understanding of these reservoirs and how to model the fracture systems quantitatively and create a Static Conceptual Fracture Model has advanced. Today, using the Static Conceptual Fracture Model as input in reservoir simulations allows the explanation of previous production behavior and the prediction of future reservoir response. These models require compilation and integration of numerous data types derived from multiple observations and discipline sources.

This atlas by Lorenz and Cooper looks exclusively at one of these observational sources, that of core evaluation. For many studies, this is the “ground truth” of subsurface fracture characteristics. However, what can be seen in the core from the perspective of fractures is a mix of what is in the subsurface and what has been done to the core during and after the coring process. These “artifacts” must be omitted from descriptions as not naturally occurring, and the strong point of this atlas is in learning how to make this distinction.

This book describes the characteristics of individual fractures as they are expressed in cores cut from hydrocarbon reservoirs, and it provides criteria for distinguishing the various fracture types as they are expressed in the limited fracture samples intersected by those cores. Different natural fracture types have different effects on reservoir permeability, and induced types have little or no effect at all, so it is imperative to correctly interpret cored fractures if the goal is ultimately to understand the broader fracture system and its influence in enhancing or degrading reservoir permeability.

The butts and slabs from a 30-ft-long, 4-inch diameter core comprise a significant amount of material when laid out in the lab for detailed examination, but volumetrically this is a miniscule sampling of a reservoir. Thus it is imperative to maximize the amount of data obtained from the few fractures captured from such a small sampling of a reservoir, as well as to correctly interpret those fractures.

The fractures described in this volume are the building blocks for the fracture networks and systems that influence reservoir permeability. The book presents examples of the wide range of fracture types and characteristics that influence reservoir permeability so that they can be recognized in cores and used to construct both conceptual and numerical models of research.

Divided into three parts (Natural Fractures, Induced Fractures and Artifacts), the book contains sections on: Extension Fractures, Shear Fractures, Other Types of Natural Fractures, Mineralization, Irregular Crack Networks, Pinion Holes, Microfractures, Deformation Bands, and much more.

This volume is an ultimate resource for reading the story and history of fractures in rocks from core. It is a “must-have” volume for all who have, or wish to have, an intimate knowledge of the rocks they work with from a fracture point of view.