Natural and Induced Fractures in Core: Recognition, Uses, and Analysis

Abstract

Fifty examples of natural and drilling-induced fractures in core, plus coring-related artifacts, are used to illustrate methods for differentiating fracture types in cores, techniques for maximizing the amount of fracture data obtained from cores, and concepts for extrapolating laterally to develop conceptual and numerical fracture-network models for a reservoir. Cores contain a wealth of information on fractures and stresses, but they comprise such a small sampling of a reservoir that fracture data collection must be optimized by knowledgeable and detailed core analysis. The samples illustrate natural fracture characteristics such as heights, spacings, terminations, widths, apertures, and orientations relative to each other and to the in situ stresses. Examples of drilling-induced fractures highlight their diagnostic characteristics and demonstrate the utility and wide variety of petal and centerline fractures. The samples also illustrate the differences between natural and induced fractures, and the sometimes subtle differences between natural shear and natural extension fractures. Coring-related artifacts such as bit impressions at core tops, core-bottom stumps, spinoffs, spiraling scribe lines, and fractures created by scribe knives provide insights into the coring process and depth-correlation points to orientation surveys and downhole logs. This collection of fractures and artifacts in cores is the starting point for an Atlas of Induced and Natural Fractures in Core.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015