Page 21 - Fundamentals of Gas Shale Reservoirs

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GAS SHALE: GLOBAL SIGNIFICANCE, DISTRIBUTION,
AND CHALLENGES

Reza Rezaee and Mark Rothwell 2
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1 Department of Petroleum Engineering, Curtin University, Perth, WA, Australia
2 HSEassist Pty Ltd, Perth, WA, Australia

1.1 INTRODUCTION country, which is followed by a statistical assessment of
certain data subsets to illustrate where shale gas is located,
The central geological properties of a shale gas play are the expected range of properties in terms of TOC, depth, age,
generally assessed in terms of depositional environment, and basin type.
thickness, organic geochemistry, thermal maturity, miner­ There are a number of key challenges that the industry
alogy, and porosity. The key features of successful shale faces, including environmental issues and commercial chal­
gas plays include high total organic carbon (TOC) content lenges. The key issues relate to the management of the
(>2%), thermally mature (Ro 1.1–1.5%), shallow for the hydraulic fracturing process, the prediction and improve­
given maturity, and a low clay content/high brittle mineral ment of EUR/well, and the consideration of variable
content. However, porosity, in situ stress regime, stress his­ production costs in different regions.
tory, and mineralogy are also significant factors.
Technically recoverable (although not necessarily eco­
nomically recoverable) gas shale is abundant across the 1.2 SHALE GAS OVERVIEW
globe. It is also located in a very wide range of geographical
regions, and in many of the nations with the highest energy In very simple terms, shale gas refers to gas produced from
consumption. For certain nations, shale gas therefore has the fine‐grained gas‐prone sedimentary rocks (i.e., organic‐rich
potential to reduce energy prices and dependence on other shale) (Lakatos and Szabo, 2009). Shale gas is considered an
nations, hence impact on both the political and economic “unconventional” gas resource, since conventionally gas is
outlook. However, the prospects for and significance of produced from granular, porous, and permeable formations
shale gas are greater where there is a lack of existing conven­ (i.e., sandstone), within which gas can readily flow. Although
tional gas production, where there is proximity to demand shale gas is considered an unconventional hydrocarbon
(i.e., population), and where some form of existing gas dis­ resource, the gas produced essentially serves the same
tribution infrastructure exists. market (Staff, 2010). The term “unconventional,” therefore,
The definition of a “resource” can follow a number of only refers to the rock from which the natural gas produced
classifications. However, in the context of this chapter, the in this particular case.
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class of “technically recoverable resources” (TRRs) has been In a conventional gas play, gas shale is often present,
adopted, which includes both economic and uneconomic but it serves as the source rock rather than the reservoir.
resources.
The assessment of the global data included the identi­ 1
For the purposes of this document, “shale gas” refers to the hydrocarbon,
fication of the shale depositional environment and basin type. whilst “gas shale” refers to the geologic material from which the gas is
A brief summary of the shale gas plays is presented for each extracted in a shale gas play.

Fundamentals of Gas Shale Reservoirs, First Edition. Edited by Reza Rezaee.
© 2015 John Wiley & Sons, Inc. Published 2015 by John Wiley & Sons, Inc.