American Oil and Gas Reporter - February 2018 - 76

SpecialReport: Gulf of Mexico Update
Proppant pack permeability is the primary factor impacting frac pack well
productivity. In frac pack operations, a
viscous fluid is used to break the formation
and transport the proppant. After treatment,
the viscosity of the fluid must break completely and flow back to the surface. If
the fluids do not break efficiently, they
can leave gel residue in the propped fractures and proppant pack, impairing production. If left in the fracture, the fluids
concentrate in the proppant pack and
leak into the porous formation, decreasing
permeability and conductivity.
Typical additives in a fracturing treatment include some type of surfactant to
reduce surface tension and maximize load
water recovery. However, surfactants have
limitations. While they alter interfacial
surface tension on both sand grains and
the formation face, the effect is temporary
and they can plate off quickly, treating
only a portion of the sand pack. Surface
wettability changes through time still
may lead to water blocking within the
proppant pack, hurting the overall conductivity.
Permanently modifying the proppant
surface can improve proppant pack conductivity and speed well cleanup. The
major causes identified with conductivity
loss in the proppant pack include proppant
flowback, fines and gel damage. Resin
coating increases conductivity by decreasing proppant flowback and reducing
polymer damage inside the pack. Other
methods use superhydrophobic chemicals

to directly treat proppant surfaces or as
additives in the stimulation fluid treatment
while proppant is pumped. These additives
have shown the biggest benefit in immobilizing fines.
Coatings or surface modifiers of super-hydrophobic nature have decreased
well cleanup time and improved conductivity, but they have not been proven to
assist in overall fluid flow of both oil and
water in the proppant pack leading to optimized dual-phase flow. This mechanism
is necessary to optimally decrease capillary
forces and ensure that neither oil nor
water gets trapped in the pack and degrades
overall permeability and conductivity.
If the stimulation fluid and produced
water do not attach to the surface of the
proppant, the cleaning is easier, minimizing
damage within the pack. Furthermore, if
the surface is oleophobic, hydrocarbons
will not attach to the surface and will
move more easily. In such a case, the
capillary pressure is null for both waterand hydrocarbon-based fluids, keeping
the pores wide open for flow. Using a
proppant that is simultaneously hydrophobic and oleophobic will assist not only in
stimulation fluid load water recovery, but
also potentially positively impact hydrocarbon flow.
Deepwater Application
A neutral wet lightweight ceramic
(LWC) proppant with a 30/50-mesh particle size distribution was used in a frac
pack completion in the Gulf of Mexico.

FIGURE 1
Surface-Modiﬁed 30/50-Mesh LWC Proppant

This well had very low bottom-hole pressure, low reservoir energy, and was not
using gas lift. The goal of treating with
the neutral wettability proppant was to
eliminate capillary pressure within the
proppant pack and reduce the effective
pressure necessary to flow the well.
The assumption was that since conventional proppant is water-wet, it would
capture some amounts of fracturing fluid
on its surface. The corresponding pore
spaces then would be occupied with the
viscous fluid, thereby slowing fluid flow
and affecting relative permeability. Because of the high affinity between the
fluid and the proppant surfaces, more
time is required to recover the majority
of the stimulation fluids pumped into
the well. Permanently surface-modifying
the proppant to a neutral wettability state
decreases the intermolecular forces between the surfaces and the fluid, leading
to an easier flow.
The proppant used in the completion
was evaluated in the laboratory for compatibility with the fracturing fluid and
for its cleanup properties through the
proppant pack. When applied in the frac
pack operation, stimulation flowback data
and first oil recovery data were recorded.
Early results indicate that the new
proppant surfaces not only reduce water
saturation, but also improve oil mobility.
These observations show promise for
permanently modifying surfaces as "nextgeneration" products for improving flow
and decreasing the risk of formation damage caused by fracturing fluids left behind
after treatment. When the proppant was
applied in the Gulf frac pack completion,
flowback was efficient, with rapid recovery
of all pumped fluids.
In this case, the initial results indicate
that the proppant surface reduced the intramolecular forces between the proppant
and the fracturing fluid, eliminating capillary pressure within the frac pack and
leading to more efficient and quicker
fracturing fluid flowback compared with
native state proppant. Moreover, first oil
breakthrough occurred earlier than on
other wells in the same area.
Neutral Wettability Proppant
Wettability describes a solid's preference to be in contact with one fluid
rather than another. A drop of a preferentially wetting fluid will displace another
fluid, and at the extreme, will spread
over an entire surface. Conversely, if a

76 THE AMERICAN OIL & GAS REPORTER

American Oil and Gas Reporter - February 2018

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