Page 98 - Principles of Applied Reservoir Simulation 2E

Part I: Reservoir Engineering Primer 83

h net thickness of reservoir [ft]
4> porosity [frac]
AF pressure depletion [psia]
If properties like compressibility are measured hydrostatically, they should be
corrected to uniaxial compressibilities [Teeuw, 1971] so that the subsidence
estimate becomes

A/z =

where V is Poisson's ratio and the subscript u denotes uniaxial compressibility.
The correction for uniaxial compaction recognizes that reservoirs with large
lateral dimensions relative to their vertical thickness deform mainly in the
vertical direction.
In many cases, subsidence has little or no adverse environmental effects.
In some cases, however, subsidence can be a significant concern. For example,
a pressure maintenance program in a field where surface subsidence is a likely
consequence of pressure depletion can improve resource recovery and help avoid
economic liabilities resulting from damage caused by surface subsidence.
Subsidence in the Long Beach, California, area due to production of the
Wilmington field had to be mitigated with a pressure maintenance program.
Subsidence has been responsible for production induced seismicity in
areas such as the Rocky Mountain Arsenal near Denver, Colorado, where
production induced seismicity was identified as the cause of earthquakes.
Earthquakes due to natural causes have led to fatalities in tectonically active
areas like the Sea of Okhotsk, offshore Sakhalin Island, Russia. Development
activities in tectonically active areas, such as offshore Sakhalin Island, need to
anticipate the impact of subsidence and production induced seismicity as part
of their reservoir management plans. Examples of compaction studies are
presented by Fredrich, et al. [1998] and Settari and Walters [1999].

Sustainable Development
Failure to adequately consider environmental issues can lead to both
tangible and intangible losses. Intangible losses are difficult to quantify, but can
include loss of public support for an otherwise economically viable project.