Open hole gravel packing of reservoir sections drilled with oil based
fluid is traditionally performed with an aqueous carrier fluid. This typically
involves displacing oil based fluid to aqueous fluid once the gravel pack
screen is in place. In reservoirs with swelling or unstable shale, this
approach reduces the risk associated with open hole exposure to aqueous fluid
over time. However, experience has shown that instability can still occur,
resulting in an incomplete or even an aborted gravel pack. In addition, mixing
of incompatible oil and water based fluids downhole has the potential to
generate very viscous emulsions that negatively impact gravel pack efficiency
and well productivity. The objective of the new technology was to maintain
borehole stability, eliminate fluid incompatibility and enable a complete
An oil based carrier fluid has been developed and qualified using
laboratory and yard scale testing. The fluid is a solids free invert emulsion
that exhibits near Newtonian rheological behavior; thereby promoting settling
of proppant during gravel packing. The density of the fluid is controlled by
adjusting the volume fraction and density of the brine phase. The fluid has
been qualified up to a density of 1.25 SG with further potential to achieve a
density of 1.63 SG.
The oil based carrier fluid has been introduced on a mature field, with
a long history of gravel pack completions. Progressive reservoir depletion has
created operational challenges, resulting in inconsistent gravel pack
performance. Consequently, several procedural changes have been implemented
over time. Reservoir inclination is typically up to 50°, open hole length
up to 200 meters, and bottomhole static temperature around 90 degC. Gravel
packs were most recently performed with a 1.10 SG aqueous carrier fluid.
The new carrier fluid has exhibited stable properties during
implementation on multiple well completions. Gravel pack efficiencies have been
consistently good, at 100% or higher. As a result, well productivity
expectations have consistently been achieved or exceeded. The operational time
for installing the lower completion compares well with the traditional approach
with aqueous fluid.
The implementation of oil based gravel packs in multiple wells allows a
comparison with brine based gravel packs in the same field. It is therefore
considered to be an industry first.
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