Microseismic
man made
Man-made microseismicity
is usually induced by high-pressure injection in ahydrocarbon
reservoir
for deliberately fracturing rock and increasing the permeability and
porosity of
underground formations surrounding a producing well and the flow of oil
and/or gas
to the well.
Microseismic
monitoring has also been used in the surveillance of accidents
related
to heavy-oil production, such as well-casing failures, cement cracking, and
unintended
fluid flow
Development of microseismic
•it has helped hydraulic fracture
stimulation to transform huge
volumes of previously uneconomic rock into productive hydrocarbon
reservoirs (Stewart,
2009). Stimulated production from methane-rich coal beds, gasbearing shales, and tight sandstone formations has
contributed hugely to the continued
growth of the oil and gas industry
worldwide.
How
It
Works
Microseism
theory is rooted in earthquake seismology. Like earthquakes,
microseisms emit elastic waves—compressional (“p-waves”)
and shear (“s- waves”), but they occur at much higher frequencies
and generally fall within the acoustic frequency range of
200
Hz to more than 2000 Hz. A hydraulic fracture induces an increase
in the formation stress proportional to the net fracturing pressure
as
well as an increase in pore pressure due to fracturing fluid
leakoff.
Hydraulic stimulation of reservoirs
Hydraulic stimulation is a
technique to induce fractures in hydrocarbon and geothermal reservoirs.
•It is injection of fluids under
high pressure in order to overcome minimum stress and open a hydraulic
fractures, either by opening existing fractures or producing new ones.
•It increases the permeability of
the rock from microdarcy to millidarcy
range.
•The
fluid injected into the formation is typically composed of brine (95%), additives, proppant
(e.g. resin-coated sand, ceramic materials).
•The stimulated volume can extend
several hundred meters around the well. The
dimensions, extent, and geometry of the induced fractures are controlled by pump rate, pressure, and viscosity of
the fracturing fluid.
•Reservoir hydraulic stimulations
usually induce (significant) microseismic
activity.
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