METHOD FOR THE OPTIMALIZATION OF THE SUPPLY OF CHEMICALS

PROCEDE D'OPTIMISATION DE L'APPORT DE PRODUITS CHIMIQUES

English Abstract

A method for optimising the use of chemicals, in particular the use of
antifoaming agents and emulsion breakers, for gas/oil/water fluid in oil
processing plants on the seabed, onshore or offshore. The chemicals are dosed
on the basis of the effect they have on the thickness of the foam layer and
the emulsion layer, respectively, of the fluid. The fluid may expediently be
supplied to and separated in a separator (1); the measurement of the emulsion
and foam layers is performed by a measuring device (3), which emits signals to
a control device (4), which controls the operation of pumps (5, 6), which, in
turn, pump, at all times, the measured quantity of chemical to the fluid to be
separated.

French Abstract

Procédé d'optimisation de l'emploi de produits chimiques, en particulier d'agents antimousse et d'agents désémulsionnants dans un fluide gaz/huile/eau dans des installations de traitement du pétrole sur le fonds marin, à terre ou au large. Le dosage des produits chimiques est fonction de leur effet sur l'épaisseur de la couche de mousse et de la couche d'émulsion du fluide, respectivement. Le fluide peut être opportunément introduit et séparé dans un séparateur (1). La mesure des couches d'émulsion et de mousse se fait au moyen d'un dispositif de mesure (3) qui émet des signaux vers un dispositif de commande (4) pilotant le fonctionnement de pompes (5, 6) qui débitent elles-mêmes en permanence la quantité mesurée de produits chimiques dans le fluide à séparer.

Claims

6
Claims
1. A method for optimising the use of chemicals, in particular the use of
antifoaming
agents and emulsion breakers, for gas/oil/water fluid in oil processing plants
on
the seabed, onshore or offshore.
characterised in that
the chemicals are dosed on the basis of the effect they have on the thickness
of
the foam layer and the emulsion layer, respectively, of the fluid.
2. A method in accordance with claim 1,
characterised in that
the chemicals are an antifoaming agent and/or an emulsion breaker.
3. A method in accordance with claims 1 and 2, in which the fluid is supplied,
via a
supply line (2), to a separator (1) and is separated in the separator (1),
characterised in that
the measurement of the emulsion and foam layers is performed by a measuring
device (3), which emits signals to a control device (4), which controls the
operation of pumps (5, 6), which, in turn, pump, at all times, the measured
quantity of chemical to the fluid to be separated.
4. A method in accordance with claim 3,
characterised in that
the chemicals are added in the supply line (2).
5. A method in accordance with claims 3 - 4,
characterised in that
a water-cut meter (11) on the outlet line (14) measures the water quantity in
the
separated oil phase and an oil-in-water meter (12) on the outlet line (15)
measures the oil concentration in the separated water phase flowing from the
separator (1); these measurements are used in the adjustment algorithms in the
control device (4) to improve the precision of the control method.

Description

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1
Method for the optimalization of the supply of chemicals
The present invention concerns a method for optimising the use of chemicals,
in
particular the use of antifoaming agents and emulsion breakers, in oil
processing plants
on the seabed, onshore or offshore.
Auxiliary chemicals such as antifoaming agents and emulsion breakers must
virtually
always be used in the processing of oil, where the separation of gas, oil and
water is a
main operation.
Such auxiliary chemicals are dosed manually today by the pumps being adjusted
up
and down on the basis of rates through the plant and the degree of foaming and
separation problems in the process, assessed visually and subjectively on the
basis of
the operating situation in the plant. The common method of adding auxiliary
chemicals
is to adjust the dosage when problems are discovered. Days often pass between
adjustments. Psychologically, it is easier to increase the dosage when
problems are
experienced than to reduce it. As finding the optimal point entails both
reducing and
increasing the dosage by trial and error, this is an operation that is very
difficult to carry
out. A chemicals company is therefore often called in and, for example, this
company
finds a new chemical.
Such practice is imprecise and often leads to the overdosing of auxiliary
chemicals,
chemicals that are often characterised as environmentally harmful.
The present invention represents a method for dosing chemicals that produces
precise
addition of chemicals and thus reduces the costs of such chemicals and spares
the
environment from unnecessary and harmful discharges.

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2
The present invention is characterised in that the chemicals are dosed on the
basis of
the effect they have on the thickness of the foam layer and the emulsion
layer,
respectively, of the fluid, as defined in the attached claim 1.
Dependent claims 2-4 define advantageous features of the present invention.
The present invention will be described in further detail in the following
with reference to
the attached drawings, where:
Fig. 1 shows a diagram that illustrates a typical dosage/effect relation.
Fig. 2 shows a diagram of a separator tank with an associated diagram that
illustrates the composition of the various layers in the tank,
Fig. 3 shows a diagram of the method in accordance with the present invention,
Fig. 4 shows an alternative embodiment of the solution shown in Fig. 3, and
Fig. 5 shows a typical dosage curve for the method in accordance with the
present invention.
Up to today, it has been common only to use simple level and interface sensors
plus
temperature and pressure meters in separators, for example separators for the
separation of water from oil.
However, in recent years, it has become more common to install one or more
density
profile meters, which, in addition to the liquid surface and the oil/water
interface, also
register the density profile through the separator. This provides quantitative
information
on the intermediate phases in a separator such as the foam phase and emulsion
phase
(see Fig. 2).

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3
There are currently several principles on the market that are used in
commercial density
profile meters:
Meters that are based on multilevel gamma radiation (sources and detectors).
Meters that are based on multilevel capacitance measurement.
Meters that are based on multilevel induction measurement.
In addition to density profile meters, water-cut meters, i.e. meters that
measure the
quantity of water in oil in an oil/water fluid flow, are becoming part of the
standard
instrumentation of separators.
The principal idea of the present invention is to control the dosage of
chemicals, in
particular antifoaming agents and emulsion breakers, on the basis of the
effect they
have on the thickness of the foam layer and emulsion layer, respectively, in
the
separator.
The effect of the chemicals is generally dependent on the dosage. Most
chemicals have
an "optimal" dosage that produces the greatest effect at an optimisation point
as shown
in Fig. 1. The vertical axis in Fig. 1 shows the effectiveness of a chemical,
while the
horizontal axis shows the dosage. As the figure shows, both overdosing and
underdosing will produce a reduced effect. It is therefore important to dose
correctly at
all times.
Fig. 2 shows a diagrammatic example of a gas/oil/water separator in which the
content
of the separator may be, from top to bottom, gas, foam, oil, emulsion (of
water and oil)
and water. To the right of the separator is a corresponding diagram
illustrating the
relation between height and density for the various layers.
The method in accordance with the present invention involves controlling the
dosage of
chemicals, in particular antifoaming agents and emulsion breakers, on the
basis of the
effect they have on the thickness of the foam layer and emulsion layer,
respectively, in
the separator. Fig. 3 shows a diagram of the method on which the present
invention is
based. Gas/oil/water are supplied to a separator tank 1 from a well or similar
(not

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4
shown) via a supply line 2. Various layers of gas, foam, oil, emulsion and
water are
formed in the tank. A measuring device 3 registers the state of the various
layers and
emits a signal to a control device 4, which, in turn, controls pumps 5 and 6.
These
pumps pump the necessary quantity of chemical (antifoaming agent or emulsion
breaker) from the reservoirs 7, 8 to the supply line 2 via lines 9, 10 on the
basis of the
signals from the control device 4.
The control criteria for the method in accordance with the present invention
may, for
example, on the basis of what is shown in Fig. 3, involve:
- minimising the thickness of the foam and emulsion layers, i.e. maximising
the possible
separation in the separator on the basis of the addition of chemicals, and
- meeting maximum requirements for the thickness of the foam and emulsion
layers in
the separator, i.e. minimising the use of chemicals on the basis of the
separation ability,
of the separation system.
The method requires measurement, using the measuring device 3, of the density
profile
over the height of the separator, showing the thickness of the foam and
emulsion layers.
Fig. 4 shows an alternative solution in which a water-cut meter 11 is arranged
on the
outlet line 14 to measure the water quantity in the separated oil phase and an
oil-in-
water meter 12 is arranged on the outlet line 15 to measure the oil
concentration in the
separated water phase flowing from the separator 1. These measurements may, to
good advantage, be entered in adjustment algorithms in the control device 4 to
improve
the precision of the control method.
However, the actual dosages required for the antifoaming chemical and the
emulsion
breaker vary continuously with major properties and process parameters such
as:
The chemical interface (gas/liquid and oil/water interfaces) is a result of
all surfactants in
the oil and water phases. Auxiliary chemicals such as shell inhibitors,
hydrate inhibitors,
wax inhibitors and corrosion inhibitors are all more or less surfactive, and
changes in
their dosages affect the chemical composition of the gas/liquid and oil/water
interfaces.
In addition, the chemical composition will also be affected by the water-cut
and the
gas/liquid ratio in the process flow (since the interface concentration is the
quantity of

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surfactant divided by the interface area in the system). Other major
parameters that
affect the interface chemistry are system pressure, system temperature and
well
composition (since the oil composition may vary in the reservoir).
The interface area consists of the gas/liquid and oil/water interface areas,
i.e. the total of
5 the drop and bubble surfaces, respectively. The interface area for the foam
phase is
also determined by the flow rate, the gas/liquid ratio and the bubble size
distribution.
The interface area for the emulsion phase is also determined by the flow rate,
the water-
cut and the drop size distribution.
The properties and parameters that determine the dosage required for
antifoaming
agents and emulsion breakers are numerous and very complicated (often
impossible) to
measure. Therefore, a practice for manual adjustment of the dosage was
previously
established.
The proposed dosing method will continuously optimise the overall effect of
all the
parameters and the properties as stated above, and the method in accordance
with the
present invention will, therefore, ensure perfect dosing at all times.
The saving on chemicals when using the method in accordance with the present
invention may be significant, as suggested in Fig. 5, in which the diagram
shows dosing
in a separation process for oil/water over a period of time. The dotted line
shows the
addition of chemicals using the manual adjustment method commonly used at
present,
while the unbroken line shows dosing for the corresponding process using the
method
in accordance with the present invention.
30

Representative Drawing