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A REVIEW OF THE CRITICAL ISSUES SURROUNDING
THE SIMULATION OF TRANSPORT AND STORAGE IN
SHALE RESERVOIRS
Richard F. Sigal, Devegowda Deepak and Faruk Civan
Mewbourne School of Petroleum and Geological Engineering, The University of Oklahoma, Norman, OK, USA
12.1 INTRODUCTION the corresponding formulations for conventional rocks that are
characterized by significantly larger pores. Under some condi
In the past decade, production of hydrocarbons from organic‐ tions, the molecule–wall interactions tend to be more impor
rich shale reservoirs has exploded onto the world energy tant than the intermolecular interactions within the fluid that
landscape. These unconventional reservoirs are now recog have traditionally formed the basis of quantifying fluid PVT
nized as forming an abundant worldwide resource that has properties, transport, and storage. For shales, the small size of
already significantly changed the face of the energy landscape the pores restricts the pore to contain only a relatively few mol
in the United States. Initially, production from these reservoirs ecules whose behavior in this confined environment may not
was mainly dry gas, but exploration and development activity satisfy the assumptions of classical thermodynamics.
has largely moved to production of condensates and oils in Organic shale reservoirs by their nature contain significant
many parts of the continental United States. The focus of this volumes of organic material that are matured enough to pro
chapter is on the modeling and simulation of transport and duce and expel large volumes of hydrocarbons. They therefore
storage in shale reservoirs. have both a complex wettability structure and support
The economic development of shale reservoirs is largely significant hydrocarbon storage in an adsorbed state on some
attributed to the introduction and maturation of two technol pore walls; and at some stage in their evolution, they also have
ogies: massive hydraulic fracturing and long reach horizontal extensive natural fracture systems produced by the process of
wells. Because of the very low permeability of shales, these expelling the hydrocarbons. For a simulator to fully capture
completion and drilling schemes are considered the predomi the complexity of organic‐rich shale reservoirs, it must accom
nant reasons for the successful development of organic shale modate potentially two fracture systems with different prop
reservoirs, and other tight gas and oil resources in the United erties and also at least two pore systems with dramatically
States. In general, because of the ultra‐low permeability of different wettability character and pore size distributions. The
shales, the well architecture and the fracture geometry, including connectivity of these various reservoir components will differ
the hydraulic fracture and reactivated natural fracture networks, among reservoirs and often may not be well known, so the
produced by the stimulations are considered to completely connectivity issue must remain as a parameter that can be
define well drainage volumes within the reservoir. adjusted in history matching, as demonstrated by the exam
The very low matrix permeability of the shale reservoir ples given in the upscaling section later. The introduction of a
rocks is a consequence of a pore geometry that includes pores more realistic microgeometry must be accompanied by other
less than an order of magnitude larger than a methane mole modifications. At the least, the equations that define hydro
cule. Studies have shown that pore proximity effects in nano carbon storage, transport, and the equations of state also must
pores can potentially alter the behavior of reservoir fluids. be modified. Adsorption on the pore surface, which for a gas
Fluid phase behavior and transport deviate significantly from depends on the pore pressure, alters the pore space available
Fundamentals of Gas Shale Reservoirs, First Edition. Edited by Reza Rezaee.
© 2015 John Wiley & Sons, Inc. Published 2015 by John Wiley & Sons, Inc.
