Page 189 - Fundamentals of Gas Shale Reservoirs

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GEOMECHANICS OF GAS SHALES

Vamegh Rasouli
Department of Petroleum Engineering, University of North Dakota, Grand Forks, ND, USA

8.1 INTRODUCTION Recent success in exploration and production from
unconventional gas shale reservoirs can be attributed to
Gas shale reservoirs have recently been the subject of many scientific study, engineering innovation, advancements in
studies in various countries due to energy shortage and energy technology risk taking, and so on. Although the concepts and
prices (Hartwig et al., 2009; Jiang et al., 2010; Jingzhou et al., technologies related to these reservoirs are now mature, and
2011). Gas shale reservoirs are the second largest unconven­ there is considerable experience given from similar basins
tional energy resource after heavy oil. The term “play” is used worldwide, basin conditions are unrepeatable, so it will be
by the energy industry for the gas shales to indicate a specific very hard to apply a single model of productive gas shale
area targeted for exploration as they believe that there is an to any other reservoirs even in the same field. Thus, every
economic quantity of natural gas located there. According to shale reservoir has its own separate exploration development
the United States Geological Survey (USGS) estimation, gas and strategy. Here, development of gas shale depends
shale can hold up to 460 Tcf of gas (Ross and Bustin, 2008). mainly on geological, geochemical, and engineering studies
However, production from gas shale reservoir as a source (Montgomery et al., 2005). In fact, geological and geochem­
rock is very recent in Australia, where most gas shale reser­ ical assessments are some basic tasks for exploration and
voirs are located in Cooper Basin in South Australia, and the development of gas shale reservoirs. This is because geolog­
Perth and Canning basins in Western Australia. There are at ical analysis can identify and characterize the portions of
least two main reasons why these types of reservoirs are more shale, while geochemical data is used to explain shale poten­
attractive compared to other energy resources: (i) its low tial as well as observing patterns of productivity. Engineering
levels of carbon dioxide (CO ) emission and (ii) the very low studies in these cases, on the other hand, help us to deter­
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level of sulfur dioxide contents. As a matter of fact, mine the geomechanical parameters of gas shale reservoirs
development of shale gas has the advantage of being a great for developing hydraulic fracture schemes to increase the
resource, with long life and production cycle (Daixu et al., productivity. However, substantial differences exist between
2011; Xinjing et al., 2007). It is also a very good solution to gas shale reservoirs and conventional reservoirs in their
cope with climate change and to increase the economic geology, mechanical aspects, and mechanism of fracture ini­
growth as well as energy security (Jiang et al., 2010; Ma et al., tiation, which have not yet been well understood, leading to
2011). Among the different parameters indicating whether the lack of quantitative technical basis for design and imple­
shales have potential to be a gas resource, organic matter mentation of hydraulic fracturing in this type of reservoir
abundance, type and thermal maturity, porosity–permeability (Gregory et al., 2011). The aim of this chapter is to present
relationships, pore size distribution, and brittleness and its different petrophysical, mechanical, and seismological
relationship to mineralogy and rock fabric are some of the studies carried out on gas shale reservoirs. This is expected
important ones (Josh et al., 2012). to provide a better understanding of the impact of

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