This present proposal was submitted to BP on 15-5-2010 during the crisis in the Gulf of Mexico.

1. PROPOSAL
FOR TACKLING THE OIL LEAKAGE FROM THE DEEPWATER HORIZON FIELD
By: Antonis Daskalakis, Offshore Engineer, Phd,
Offshore Energy Systems SA, Greece
14-05-2010
1. Introduction
This present report contains a proposal for tackling the oil leakage from the well head of the
Gulf of Mexico oil field of BP.
The idea may be wrong but there is no time for more analysis from my part. It is better that the
concept presented here will be examined by more experienced and more knowledgeable
engineers of BP instead of waiting to prove everything myself, just to publish a paper after the
disaster. There is no time left for the environment.
The idea contained here came to me since I am working on a project for compressed air storage
in big balloons in the sea bottom as intermediate energy storage produced by renewable energy
sources (wave, wind).
In short the concept is to lower a big balloon over the well head to capture the oil coming out
and pump it to the surface to a tanker or other proper storage facility.
The balloon will be open at its bottom, it will be covered by a strong net which will be attached
to a steel structure of proper design and weight which will be driven to seat on the sea bottom
over the well head.
The balloon is not meant to seal the well head as this will be difficult or unachievable due to
high pressures (and temperatures) of the oil coming out from the well head. However I believe it
is not required to seal the well, as it is explained below, in order to capture the oil.
The balloon will stand above the well head to a short distance (gap), held there by the net which
is attached to the steel structure, seated on the bottom.
The oil will be pumped to the surface through a flexible pipe held upright by floaters properly
distributed along it. The pumping can be done naturally due to the difference of densities
between water and oil, or it may be helped by a pumping arrangement on the storage facility.
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2. 2. Concept description
Sketch 1 shows the balloon over the well head. From the sketch the following can be seen.
1. The steel structure which will anchor the balloon over the well head. The steel structure
is a circular construction which partially penetrates the soil mainly for increased holding
capacity.
2. The balloon is made by strong polyethylene or other proper material. The dimensions of
the balloon are to be determined by the data of the well as can be discussed later.
3. The net which undertakes the buoyancy forces in a uniform manner, as well as current
forces acted upon the balloon and transfer to the steel structure.
4. Sinker weights which will hold the balloon over the steel structure even if there is no
pressure inside the balloon and it is in a slack condition. The sinker weights can also be
additionally anchored on the sea bottom providing additional support to the balloon.
However the sinker weights can also act as shock absorbers in case of a blasting or a
rapid change of pressure inside the balloon.
5. The flexible pipe which will lead the oil to the surface. The pipe is in fact a flexible riser
and there is great experience in the industry for the design, construction and installation
of such systems.
6. The floaters which will keep the pipe in upright position and will take its weight
uniformly avoiding overstresses.
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3. Sketch 1. Balloon anchored above the well head
As was mentioned above the balloon will be open at its bottom and the bottom opening will be
allowed to be in a distance from the steel structure so that there is a gap between well head and
the balloon opening.
Therefore there is no sealing of the well head. As the oil is coming out from the well, as an oil
beam with high speed (defined by the reservoir characteristics), it will come inside the balloon
like a squirt.
The total pressure of the beam at the well head will be equal to the pressure of the water at the
sea bottom (for 1500 m water depth approximately 150 bar).
Since the speed of the oil beam, I assume, will be high the static pressure due to Bernoulli will
be less than the surrounding water static pressure and therefore there will be no leakage of oil
from the gap between the balloon and the sea bottom. In this way the whole amount of oil
coming out from the well will be led inside the balloon.
As the oil is lighter than water it will be gathered in the upper part of the balloon which will
gradually be “inflated” since the water pressure at the bottom of oil chamber will be higher than
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4. that at the top of the balloon. This will happen, of course, until the whole volume inside the
balloon will be captured by oil. After that the oil will again be led to the sea.
If however the oil from the balloon can be pumped out to the sea surface, in the same pace as it
comes out from the well, there will be a continuous flow of oil from the well head to the sea
surface without leakage to the sea. Can this be done?
Paying attention to sketch 2 the oil from the oil chamber will be led to the flexible pipe (riser).
Since the water pressure at the bottom of the oil chamber is higher than the oil inside the
flexible pipe the oil will be naturally pumped out of the balloon to the surface.
The real question however is if the oil flow rate inside the pipe, driven by the natural differential
pressure can be equal to the flow rate from the well. If it is less, then the balloon will be
gradually filled with oil and oil will leak to the sea from the open bottom of the balloon. If it is
more then, water will reach the surface and oil pumping will be interrupted, while the balloon
will become slack.
In the following, some calculations will be performed based on imaginary data in order to
illustrate the way one can deal with the problem and the sizing of the proposed system.
Sketch 2. Schematic functioning of the proposed set up
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5. 3. Performing some calculations
The following assumptions are made
Water depth (h): 1500 m
Reservoir pressure (Pr): 600 bar
Depth of reservoir (from the sea bottom) (z): 4000 m
Oil density (ρο): 850 Kg/m3
Water density (ρw): 1025 Kg/m3
Based on this information and Bernoulli’s equation we have
(1)
Where ur is the speed of the oil beam at the wellhead and the other symbols have been
explained before. This is a very simplified calculation it assumes a single phase oil media, no gas
content or other formations. Petroleum engineers with knowledge of the reservoir
characteristics can perform exact calculations).
In the above we assumed that the pressure at the wellhead will be equal to the water pressure
at the well head (sea bottom). This is very important and makes the difference between a sealed
chamber and a not sealed one as it is presented here.
From this equation it is possible to calculate the speed of the oil beam at the well head.
Naturally from this calculation one can also calculate the height of the squirt inside the balloon.
I suppose this height is known to the engineers of BP from observations through an ROV or from
calculations.
The size of the balloon should be such so as to allow the unobstructed development of the
squirt to avoid forces acting on the internal surface of the balloon. If it is too high one could
thing of a cylindrical shape of the balloon instead of the spherical one we show in our sketches.
From the speed and the known diameter of the well one can calculate the flow rate of oil
coming out from the well. This information is also available to the engineers of BP, but not to
me. For our demonstrative calculations we assume this diameter to be 100 mm.
From the balloon the oil is pressed to flow inside the flexible pipe due to the water pressure at
the bottom of the oil chamber. Bernoulli’s equation will then give:
(2)
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6. Where uc is the speed of the flow inside the flexible pipe and we assume pressure at the sea
surface zero and reference point at the sea bottom.
Table 1 has been included which give the assumptions made before and provide the simple
calculations using the above two equations.
The following are calculated:
• The speed of flow inside the well
• The flow rate with the assumed well diameter
• The flow speed inside the flexible pipe
Table also gives the ratio of the speed of oil flow inside the well and inside the flexible pipe. The
square root of this ratio gives the ratio of the diameters of the two pipes (diameter of flexible
pipe over diameter of well) so that the two flows are equal.
In sizing the flexible pipe one can increase its diameter and incorporate a valve at the sea
surface to control the flow rate. The control should be in such a way as to keep the balloon say
half filled (or less). In this way the balloon acts as a buffer area and its size should be such as to
provide flexibility in the whole operation and safety limits to absorb unexpected deviations of
the flow rate.
Furthermore with an assumed diameter of the balloon its volume is calculated and an
estimation of the time required to fill the balloon with oil is given (based on the calculated flow
rate of the well). This time is important at the first installation of the whole set up. Long time
will allow the steel structure to be settled on the sea bottom before buoyancy forces will
develop inside the balloon making difficult the job. Sinker weights can also help in this transient
period. Later during normal operation is an indication of the size of the buffer area and the
controllability of this operation.
In case the balloon is partially or totally filled with oil a buoyancy force will be developed on the
balloon due to the difference of the densities of oil and water. This is calculated and given in
table 1 for the totally filled balloon.
This has to be taken into account in order to calculate the required dead weights to keep the
balloon on the sea bottom.
However the required weight should be more than taking the buoyancy. On the balloon forces
will be acting, mainly due to currents. These forces have to be calculated based on current
speed measurements and the projected area of the balloon. There must be excess weight to
provide holding capacity of the steel structure to horizontal forces. This is the reason behind the
design of the steel structure which is meant to penetrate the soil increasing its holding capacity.
This can be done before an oil chamber develops inside the balloon, when there are no
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7. buoyancy forces, or by pumping out the oil from the balloon with a flow rate higher than the
flow rate of the well.
There are also some other problems and design parameters to be taken into account:
The first is oil temperature which is not known to me and what the properties of the material of
the balloon should be to withstand it. It is believed that the low water temperatures at the
depth of 1500 meters (4 oC ?) will help in cooling the upcoming oil. Temperature also is a
significant parameter in the formation of hydrates as it is discussed in the following. It is
therefore a matter to be studied by experts in the field.
Second is the case of a blasting from the well. I do not have information on the reservoir
characteristics, I do not know the probability of such an event and its nature. If such a case is
probable then one has to foresee the effects and ways to absorb it.
In the present concept a number of flexibilities are incorporated which give absorbing
characteristics to the system. These characteristics include:
1. The elastic structure of the balloon. A rigid construction cannot behave correctly in a
case of a blast.
2. The uniform distribution of pressures inside and outside the balloon and the fact that
the differential pressure is kept low during normal operation.
3. The sinker weights which will act as shock absorbers in case of a blast. This absorbing
capability can be enhanced by choosing the material of the ropes which hang the
weights.
A third problem is the formation of hydrates. The conditions for such a formation have to be
studied carefully by experts on the field. It may be possible the whole set up to be designed in a
way to avoid this formation. It can be possible to use inhibitors like ethanol, methanol or others
which can be injected inside the balloon through a second pipe from the surface (can this pipe
pass through the flexible pipe?). It also may be possible, in case such a formation is unavoidable
to pump hydrates to the surface along the oil allowing from time to time some water to be
pumped as well
There may be other problems which are not known to me and which can be solved or they
cannot. If I am informed for such problems I may have or may have not something to say on it.
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8. Table 1. Simple calculations on the concept based on imaginary data
Assumed input
information
z= 5000 m reservoir depth
Pr 600 bar reservoir pressure
Pr = 60000000 N/m2 reservoir pressure in Pascal
h= 1500 m water depth
Pw 15082875 N/m2 water pressure at sea bottom in Pascal
Pw= 150.83 bar water pressure
ρp 880.00 kg/m3 petroleum density
ρw 1025 kg/m3 water density
Well calculations
up2/2 = 1,992.19 Equation (1)
up 63.12 m/sec speed of oil flow inside well
dw 100 mm well internal diameter
Aw 0.01 m2 well section
Qp 0.50 m3/sec oil flow rate
1,784.73 m3/h oil flow rate
Flexible pipe
calculations
pressure driving oil from the balloon to the sea
ΔPn 15,082,875.0 N/m2 surface
uc2/2 2,424.6 Equation (2)
69.6 m/s speed of oil flow inside flexible pipe
rs 0.91 Ratio of speeds (well/flexible pipe)
rd 0.95 Ratio of diameters (flexible pipe/well)
Balloon
r 15 m radius of a spherical balloon
V= 14,137.2 m3 The volume of the balloon
time to fill the balloon with oil with the
time to fill 7.9 hours calculated flow rate
Buoyancy of the balloon completely filled with
dead weight 2,049,889.2 Kg oil
Additional weight required for holding
2,049.9 Tones capacity
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9. 4. Concluding remarks
A proposal is made which may give a solution of how to trap the oil coming out of the oil head of
the Deep horizon oil field in the Gulf of Mexico and how to pump it out to a storage facility.
The proposal needs elaboration to prove its applicability compared to other proposed solutions.
BP engineers who have available all necessary information can do it. The concept can also be
easily and quickly tested in a laboratory.
One major aspect is the practicality of the concept. Can it be realized quickly and be
implemented in the difficult conditions of the field and in such big water depths?
In my opinion this is possible or else I wouldn’t make the proposal. A balloon of the size
required, I believe it is possible to be constructed by companies which are dealing with the
matter, or probably a consortium of companies in the field. So is the required net.
For the flexible pipe and the associated floaters and all the necessary calculations there exist
experienced companies in the field.
A last remark is that the concept presented here could work with a rigid steel structure instead
of the balloon.
Such a structure (dome) I have seen in the news which was attempted to be installed over the
well head. I have no information on that. But if it was used to seal the well then I imagine the
high pressures developed would prevent it.
However, if the structure is installed in a way similar to proposed here, it can possibly work, i.e.
there must be a gap between the bottom of the structure and the sea bottom so as to prevent
to develop high pressures inside it. Also the height of the structure has to be large enough to
avoid collision of the oil beam on the internal dome surface and of course the rate of pumping
oil from the dome to be equal with the rate of oil flow coming out from the well.
In case that it is expected to have events like blasting or sudden changes of pressure some
absorbing capabilities should be incorporated like those described before in the case of the
balloon (see sketch 3).
I remain at the disposal of any interested party for further evaluation.
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10. Sketch 3. A way to realize the proposed concept with a dome instead of a balloon.
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