University of Oklahoma (OU) researchers are developing a new simulator for shale gas reservoirs that will provide oil and gas companies with a tool for managing production and choosing drilling locations to lower costs and increase production.
Richard Sigal, Faruk Civan and Deepak Devegowda, Mewbourne College of Earth and
Energy, are the first to systematically tackle this challenge. The project is
supported with $1,053,778 from the Research for Partnership to Secure Energy
plus an additional $250,000 in matching funds from a consortium of six oil and
gas producing companies.
has a smaller greenhouse gas effect and is less polluting than other fossil
fuels, plus gas produced from shale gas reservoirs can have a positive impact
on the U.S.
economy by replacing coal used for electrical generation, natural gas imports
and oil imports in some applications.
for conventional reservoirs are not suited for shale gas reservoirs," says
Sigal. "An example of this is the deposition of frac water used to force
the gas from the reservoir. In a shale gas reservoir, massive hydraulic
fracturing opens up the reservoir so the gas can flow. This involves pumping a
large amount of water into the reservoir. In conventional reservoirs, all this
water is produced back, but in shale gas reservoirs, only a small percentage of
the water is produced."
to Sigal, "Current commercial simulators do not successfully predict the
amount of water produced. Researchers need to model the deposition of this
water to better understand the reservoir and address concerns the effects this
water can have on shallow aquifers. One goal of the simulator project is to
determine and provide the capacity to model frac water deposition."
long-term gas production with history matching requires more accurate physics
and geology," states Sigal. "Using a new $2 million microscope at OU
to see the detailed porosity of the rocks, Professor Carl H. Sondergeld and his
collaborators have found two kinds of pore space in the rocks. Besides the
inorganic pore space where we expect to find gas, they discovered pores the
size of nanometers in the organic portion of the rock. This discovery needs to
be incorporated into the simulator design."
recognize the physics of fluid flow and storage are very different in the
inorganic and the organic portions of shale gas reservoirs. And, these
reservoirs contain both natural and induced fracture systems each with
different properties. OU researchers will develop a quad porosity model to take
into account these differences.
three basic issues with the physics of these natural non-porous systems. First,
the standard equations used to describe gas transport are incorrect in the
small pores in the organic material where a significant portion of the
hydrocarbon gas is stored. Researchers studying artificial nanomaterials have
developed new gas transport equations that need to be adapted to the
complicated pore spaces that describe shale gas reservoirs.
in standard simulators, an assumption known as instantaneous capillary
equilibrium provides the relationship between the gas and water pressure.
Equilibrium cannot be maintained because of differences in the transport rates
for water and gas in shale gas reservoirs, so the standard equations must be
modified. Finally, the very large capillary forces caused by the very small
pore size require a different treatment of relative permeability, which
controls the relative transport of the water and gas.
is a three-year project to develop the new simulator starting with the
fundamentals," Sigal remarks. "We have already developed a 1-D model.
The next step will be to build a simple 3-D testbed system. At first, we will
test this model against models run on commercial simulators."
we will build modules that incorporate the individual modifications needed for
conventional simulators to correctly model shale gas reservoirs," Sigal
comments. "These modules will be available for adoption by industry for
use in existing company or commercial simulators. Finally, we will use the
modified simulators to history match production from existing reservoirs. Our
commercial sponsors will provide data for this."
Developing a Shale Gas Reservoir Simulator
January 7, 2011