APPLICATION OF MICROSPHERES TO IN SITU SEPARATION OF WATER AND OIL

UTILISATION DE MICROSPHERES POUR SEPARER L'HUILE DE L'EAU

English Abstract

To combat the problem of water infiltration into an oil reservoir, a technique
of injecting a fluid into the reservoir to cause separation between the oil and
water is now available. This fluid will have a specific gravity matched to the
conditions of the reservoir so as to float on the water and sink in the oil. In
this way, it can be assured that the fluid will form a separation barrier between
the water and oil.
This invention contains two procedures, one to create a hard barrier and the
other to create a soft barrier.
Once the barrier is in place, it is possible to resume profitable production of
the well yet again.

Claims

CLAIMS MADE BY THIS PATENT:
1) Through the addition of light weight microspheres, those supplied by
LBG Ltd. allow for the reduction of cement densities the point where
is may float on water and sink in oil. This typically is in the
range of 0.8 to 1.1 g/cc.
2) Through high pressure injection, the cement can be forced into the
formation and allowed to settle out into the correct position. From
here, once set up, the cement will form a hard barrier that will
severely retard the initial Coning that occurs in a well. This will
afford the company to pump more oil than would otherwise have been
attainable.
3) The majority of the strength of the cement will come from the
interaction of the cement with the formation and as such the only real
strength required is the strength required to bond the cement to the
formation.
4) Selection of the additive series must include several factors, such as
density, working pressure, chemical inertness and particle size.
These four factors together will ensure the correct cement being
injected into the formation.

Description

~ / L/ g C~
DETAILED DESCRIPTION:
The eventual demise of an oil reservoir is the limit at which the oil/water
coming out from the well is uneconomlcal to separate. This point is known as the
Water Cut Off Limit (WCO%) as a perce~lt of total flow from the well.
The problem is the intrusion of the ground water into the oil reservoir leaving
it to mix with the oil. The problem is compounded by the natural welling process
known as Coning. These two problems give rise to a shortened life of the well
due to water infiltration into the reservoir.
Techniques to separate the oil from the water once it has arrived on surface are
presently utilized to allow the companies to raise the WCO%, but this is more of
a "band aid" solution to the problem.
The ultimate solution to the problem is the separation of the two fluids while
still in the hole and the spending the energy to only pump the revenue generating

21~8968
oil from the reservoir.
There have been two techniques invented to cause this in situ separation. The
hard barrier consist of ultra light density cement created through the addition
of low density microspheres that meet the required strength criteria. The
concept behind the hard barrier is to form a impermeable boundary between the oil
and water. This happens in the water/oil interface zone. Through the creation
of the barrier, the underlying water must then travel around the ends of the hard
barrier and then travel to the pump. This additional time required will afford the
company the time to make a recovery that would be higher than would otherwise
be possible with the traditional technique.
Simply stated, for this process to be economically viable, the revenue gained from
the additional oil must exceed the cost of the ultra light density cement
that was pumped into the hole to create the hard barrier.
Since water in the reservoirs have specific gravities in the range of 1.0 to 1.1
and oil ranges from 0.8 to 0.85, there is a window of opportunity to inject
cement with a density of 0.85 to 1Ø Through the addition of microspheres, it is
extremely easy to control the exact density so as to guarantee the correct
barrier creation and location.
Once the correct density is created, it can then be pumped into location with
pressures that will not damage the formation or the integrity of the microspheres.
Once the cement is set, the well may be operated normally but for a longer period
due to the reduction of the water penetration.
The additives used in the application are the LBG. Ltd Additives Series. These
microspheres meet certain conditions required by the oil industry and thus make
most practical use.
The addition of the LBG Additives HS60 and LD38 proved to ~e the most effective in

~ 21 18968
controlling the density and ultimate pumping pressures. The cement used was right
angle set industrial oil cement.
Once mixed, the cement is pumped into the reservoir and allowed to settle and
set. The setting time should be far greater than the set time since one must allow
the cement time to migrate to the correct location with in the reservoir.
Once the cement is set, production can begin on the well. The cement need not
have high strength characteristics since most of its strength will come from the
bond with the surrounding formation. This mi niml7m strength is determined from the
characteristics of the formation's rock, the pressures at depth and the density
target range for the cement.
The largest single limiting factor found was the porosity and opening size of the
formation. The larger the porosity the better the penetration of the cement in
terms of speed of displacement and settling. As the porosity is reduced, the
performance of the system becomes hampered. An important factor in the
determination of the correct LBG Ltd. Additive series is the size range of the
particles. These must be smaller than the porosity so as to allow the microspheres
entrance into the reservoir. With the reduced porosity, it is harder for the
cement to form the barrier away from the well. As the porosity is reduced, the
time allowed for cement barrier to take must also be increased. From experience,
this extra time comes from a trade off between the cost of waiting and a higher
recovery of oil from the reservoir.
Tests have been carried out to show the strengths of ultra light density cements.
From these tests it is known that the cement will provide adequate strength to the
formation so as to form a separation barrier between the oil and water.
A test cement was created having a density of 0.92 g/cc which had strengths of
2.5 Mæa in 24 hours. This cement did float in water. In this test, the LBG LD38
additive was used in a 50:50 cement to additive miy~ure. Further reductions are

2I48968
possible, but the need for them are case to case
The process can then be repeated once the well has water out again. Given an
appropriate settling time, the injection of more cement will allow the recovery of
even more oil with in the reservoir. This repetition can be repeated until such
time as the returns are less than the expenses.