In 1966, Don Ho recorded and released the hit single “Tiny
In the wine
Make me feel happy
Ah, they make me feel fine
There are more lyrics, of course,
but this is a sufficient sampling of Ho’s signature piece. However, and with all
due respect to the iconic Hawaiian vocalist, he wasn’t singing about the
tiniest of bubbles—bubbles that are too small to be seen in wine or in anything
else—nanobubbles! But to be fair, he couldn’t have known about, or even imagined,
nano-sized bubbles. The concept of nanobubbles was not proposed until 1994, to explain
the underpredicted attractive forces observed between hydrophobic surfaces in
water.1 Their existence in a solution, or even if that were
accepted, their ability to maintain their size and suspension in a solution, has
been the subject of controversy and considerable experimentation.
But for our purposes, let’s
assume that nanobubbles do exist and remain stable in a solution. There is more
than enough evidence now to support these notions—including in downhole oil and
gas well temperature and pressure conditions. With that, oilfield applications for
nanobubbles, especially in production enhancement, should be of interest.
So, how small are
Nanobubbles are under 200 nanometers (nm) in size, more typically 70 to 120 nm.
To put that in perspective, that is about 2,500 times smaller than a grain of
salt, 100 times smaller than a single dust particle or 10 times smaller than a
bacterium. There can be up to about 200 million nanobubbles in just one cubic
centimeter of water.
In theory, if not in
practice, nanobubbles can be generated with any gas in any liquid. Beyond experimental
studies, actual applications to date have mostly been nanobubbles of oxygen (or
air) in water. Water containing nanobubbles is already used in many biological
and medical applications. Nanobubbles increase the efficiency of drug and gene
delivery. Water containing oxygen nanobubbles is used in wastewater treatment,
to promote the growth of plants and animals, and as a cure for diseases caused
by anaerobic bacteria, since oxygen nanobubbles have a sterilizing
and oxidizing effect. When stimulated, the nanobubbles collapse, releasing the
hydroxyl free radical—an extremely strong oxidizer which can destroy pathogens
and pollutants, including bacteria in water.
So, why should we in the
production world be interested in nanobubbles? The reason is because of
their unique properties, compared to “normal” bubbles, and how they can be
utilized in a variety of potential “chemical-free,” safe and environmentally
sound oilfield applications, including in production enhancement.
Among the unique
properties of nanobubbles are these:
of buoyancy. Because of their tiny size, nanobubbles lack enough
buoyancy to rise to the surface. They, instead, are in Brownian motion,
remaining suspended and active in solution.
Strong negative surface
bubbles possess a surface charge, but the smaller the bubble, the
stronger the surface charge. The very high surface charge possessed by
nanobubbles greatly limits bubble coalescence, due to repelling forces. This property
also enables nanobubbles to remain stable and suspended in solution for weeks
or even months.
Surface tension reduction. Nanobubbles reduce the surface
tension of liquids, which suggests they can be an effective, “chemical-free”
replacement for surfactants—for example, in oil recovery applications.
A company making strides with
nanobubble technology in the oil field is Moleaer, which owns intellectual
property related to nanobubble generation methodology. They have developed nanobubble
generators that can saturate water (or other liquids) with nanobubbles from small-
to large-scale and at high-volume injection rates. Commercial applications of nanobubbles
in lake and pond algae control, and in soil enrichment for improved crop growth
and quality, among other special agricultural and water treatment uses and
applications, are already in practice by Moleaer.
In the oil field, Moleaer
has proven the effectiveness of nanobubbles for oil/water separation and produced
water treatment for hydraulic fracturing. Now, in conjunction with oil and gas
operators, Moleaer is delving into the application of nanobubbles to
restimulate existing wells completed in unconventional formations and to
increase oil recovery from new well completions.
One can further imagine nanobubble
applications onshore and offshore, in oil recovery, oil/water separation, produced
water treatment and on-site environmental applications. Perhaps infusing
waterflood injection with nitrogen, CO2 or natural gas nanobubbles, including
in place of conventional chemical enhancements, makes sense. Additionally, “huff-and-puff”
enhanced oil recovery applications with reactive fluid(s) infused with nanobubbles,
in conjunction with injection isolation tools, are a consideration for stimulating
long horizontal well completions or selective stimulation of oil-producing
zones, in wells producing both oil and water. Adding nanobubbles to fracturing
fluid or enhancing acid stimulation of offshore wells are applications that
would obviously come to mind.
There are surely more
potential applications of nanobubbles—with different gases and in both aqueous
and hydrocarbon liquids. The greater the imagination, the greater the
LEONARD KALFAYAN is recently retired, following over 13 years with Hess as Principal
Advisor, Production Enhancement, and Head of Production Engineering and
Stimulation. He has 42 years of global experience in the oil, gas and
geothermal industries, primarily in production enhancement, new technology
development and implementation, technical support and business development.
Prior to joining Hess in 2009, he worked for Unocal, BJ Services, and as an
industry consultant. He is a past SPE Distinguished Lecturer and SPE
Distinguished Member. He has authored over 30 SPE and other journal
publications and holds 13 U.S. patents. He also is the author of the book Production Enhancement with Acid Stimulation
(in its 2nd edition), co-author of the book The
Energy Imperative, and co-editor of the SPE Monograph: Acid Stimulation.