19
Compressibility varies for the rock, the reservoir fluid, and any connate water.
As with many measured quantities, the oil industry sometimes uses nonstandard
units to measure compressibility, in this case the microsip. A pressure change of
70 bars will result in approximately a 1% change in volume for a material with 10
microsips of compressibility. Typical sandstone has a compressibility of about three
microsips, similar to that of water (Newman 1973). The reservoir fluid itself can
show higher compressibility. Blunt (2013) estimated DWH values of about 14
microsips. Total compressibility, the sum of oil, rock, and water, was a matter of
dispute for DWH since it could be connected to an estimate of the oil released. Oil
released from the broken well was postulated to be a product of the amount of available oil in the reservoir, the total compressibility, and the pressure difference
between the reservoir and ocean floor.
Also in dispute for DWH was the connectivity of the rock pores or permeability
of the reservoir. Pores that are not connected cannot share contained fluid. Fluid
flow in the reservoir follows some form of Darcy’s law, discovered by Henry Darcy
in 1856. According to the simplest form, flow in the reservoir can be estimated as
V A
p
r
= ⋅
⋅∇
µ
η oil
(2.5)
where A = flow cross section, μ r = permeability, η oil = oil dynamic viscosity, and ∇p
= pressure gradient. Once again, units employed in the oil industry do not match
standard SI choices. Permeability is recorded in millidarcy (mD). A Darcy is
approximately 10
−12
square meters. A typical permeability number might be a few
hundred mD. However, permeability determination in reservoirs can be quite challenging and is often subject to large uncertainty.
2.4 Subsurface Release
As introduced above, a subsurface oil spill may occur from an individual well tapping
a single reservoir or may originate at a platform that connects multiple reservoirs.
Leaks may form at a single wellhead or anywhere along a subsea pipeline or riser, thus
involving either live crude oil or separated hydrocarbon and gas. The most likely types
of accidents are an offshore blowout or subsea pipeline leak. A blowout is defined as
any time the operator loses control of the flow rate in a well or pipeline.
Oil spilled from a subsea reservoir could originate from distributed or point
sources. A distributed source could be formed if a well bore lost integrity below the
seafloor such that oil percolated up through the sediments near the seabed, a matter
of concern to DWH responders that fortunately did not happen. In such a case, the
release to the water column would cover a larger area and may not include a rigorous jet of oil or rising buoyant plume. In the case of a point release, the gas and
liquid petroleum exit a small orifice, initially breaking up into gas bubbles and oil
droplets that form a buoyant plume that rises together with entrained seawater
2 The Importance of Understanding Fundamental Physics and Chemistry of Deep Oil…
Compressibility varies for the rock, the reservoir fluid, and any connate water.
As with many measured quantities, the oil industry sometimes uses nonstandard
units to measure compressibility, in this case the microsip. A pressure change of
70 bars will result in approximately a 1% change in volume for a material with 10
microsips of compressibility. Typical sandstone has a compressibility of about three
microsips, similar to that of water (Newman 1973). The reservoir fluid itself can
show higher compressibility. Blunt (2013) estimated DWH values of about 14
microsips. Total compressibility, the sum of oil, rock, and water, was a matter of
dispute for DWH since it could be connected to an estimate of the oil released. Oil
released from the broken well was postulated to be a product of the amount of available oil in the reservoir, the total compressibility, and the pressure difference
between the reservoir and ocean floor.
Also in dispute for DWH was the connectivity of the rock pores or permeability
of the reservoir. Pores that are not connected cannot share contained fluid. Fluid
flow in the reservoir follows some form of Darcy’s law, discovered by Henry Darcy
in 1856. According to the simplest form, flow in the reservoir can be estimated as
V A
p
r
= ⋅
⋅∇
µ
η oil
(2.5)
where A = flow cross section, μ r = permeability, η oil = oil dynamic viscosity, and ∇p
= pressure gradient. Once again, units employed in the oil industry do not match
standard SI choices. Permeability is recorded in millidarcy (mD). A Darcy is
approximately 10
−12
square meters. A typical permeability number might be a few
hundred mD. However, permeability determination in reservoirs can be quite challenging and is often subject to large uncertainty.
2.4 Subsurface Release
As introduced above, a subsurface oil spill may occur from an individual well tapping
a single reservoir or may originate at a platform that connects multiple reservoirs.
Leaks may form at a single wellhead or anywhere along a subsea pipeline or riser, thus
involving either live crude oil or separated hydrocarbon and gas. The most likely types
of accidents are an offshore blowout or subsea pipeline leak. A blowout is defined as
any time the operator loses control of the flow rate in a well or pipeline.
Oil spilled from a subsea reservoir could originate from distributed or point
sources. A distributed source could be formed if a well bore lost integrity below the
seafloor such that oil percolated up through the sediments near the seabed, a matter
of concern to DWH responders that fortunately did not happen. In such a case, the
release to the water column would cover a larger area and may not include a rigorous jet of oil or rising buoyant plume. In the case of a point release, the gas and
liquid petroleum exit a small orifice, initially breaking up into gas bubbles and oil
droplets that form a buoyant plume that rises together with entrained seawater
2 The Importance of Understanding Fundamental Physics and Chemistry of Deep Oil…