Rock Texture Index (RTI): Quantifying the Impact of Rock Texture and Its Mineral Composition

Abstract

The prolonged slow recovery in the oil market has continued to reduce the pace of evaluation and completion decisions in unconventional reservoirs. The industry has turned to a more science-based decision-making process for project execution. Because physicochemical and mechanical properties of rock control its behavior, a methodical rock texture characterization of core samples and cuttings can provide powerful information that can be used reliably and cost-effectively to optimize decision making based on rock characteristics. These rock properties are greatly influenced by its texture and mineral composition. Consequently, to optimize any strategy that depends on these parameters, quantifying the rock texture and its mineral composition become imperative. Several authors have attempted to predict or estimate rock behavior using approaches that are either skewed to mineral composition or texture. One of these approaches considers brittleness or fraccability. In the oil and gas industry, the quantification of the brittleness of a rock is considered to be an important parameter for optimizing horizontal well drilling, hydraulic fracturing, unconventional reservoir exploitation, and protection of fresh water aquifers from contamination. Even though rock behavior is known to be largely controlled by mineral composition and texture, recent development of a fraccability (brittleness) index has been largely skewed toward a focus on mineral composition at the expense of rock texture. In the construction and mining industry, much effort in the past focused on understanding this parameter and on quantifying and predicting the compressive strength of the intact rock. The consideration is mostly the nature of framework grains without mineral composition as part of rock textural property quantification. However, mineral composition, combined with the rock texture property, form the dominant influence on rock behavior. Both factors should be considered together. This study used thirty samples from different lithologies to describe a new understanding of the impact of rock texture and its mineral composition. The method quantifies and incorporates these properties into a new rock texture index (RTI) to assist in predicting rock behavior.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017