## Archive for **June 20th, 2010**

## June 20, 2010 DEL VALLE FORENSIC ENGINEERING INVESTIGATION OF THE HORIZON OIL WELL DISASTER AND A SOLUTION TO STOP THE FLOW OF OIL

HORIZON OIL SPILL SOLUTION-REV-06-22-10 Model (1

This report explains the oil disaster in more scientific terms and defines the terms used by the press and TV stations.

Nando

**DEL**** VALLE ENGINEERING, INC.**

**STRUCTURAL ENGINEERS**** **

# MIAMI, FLORIDA

**DEL**** VALLE FORENSIC ENGINEERING INVESTIGATION OF THE HORIZON ****OIL**** ****WELL**** DISASTER ****AND**** A SOLUTION TO STOP THE ****FLOW**** OF ****OIL**** **

June 18, 2010

The media that has covered the “Horizon Deep Oil Well disaster” has issued several statements about the oil pressure encountered in the well. Many times they have made statements that they do not know what the pressure is and that it is something that is beyond our present scope of knowledge. The rate that oil is flowing is also subject to wild numbers.

As a licensed and practicing civil engineer of the State of Florida I must say that this statement is false. The technology to solve this problem is readily available to any engineering firm in the USA that has been involved in the design or construction of extensive infrastructure projects.

To properly understand what the issues are, I am going to engage in something that is called forensic engineering.

The first thing we have to do is to define what pressure is and how pressure is acting at all points in the Horizon well.

# Definition

# atmospheric pressure noun

n [U] specialized

the force with which the atmosphere presses down on the surface of the Earth

http://dictionary.cambridge.org/dictionary/british/atmospheric-pressure

Expanding on the above definition to the case in point I will expand the above definition to pressures at the oil well outlet at 5,000 feet under the ocean.

The following data is known to the general public and the statement that BP engineers have more accurate data than this is beyond any reasonable doubt.

1 Depth of the oil well outlet is 5,000 feet from the surface of the ocean.

2 Size of the pipe 21” diameter and made of steel

3 Numerous videos shown on TV and the internet of the leaking pipe and the breaks with the oil going out. The connection of the pipe to the Blowout Preventer has also been shown. The video has shown the bottom of the ocean floor.

4 The depth of the reservoir of oil is 30,000 feet below the surface of the ocean.

From the above information I will start my investigation and with the facts uncovered I will design a structure that will close the oil well.

The design of this structure could have been more accurate if I would have had the soil reports at the well site, the details of the blowout preventer and the 21” pipe. Lacking these details I will assume the dimensions and materials that were used.

A) **INVESTIGATION**

One cubic foot of water weighs = 62.4 pounds

One cubic foot of oil weighs = 51.16 pounds

Pressure at ocean floor:

P_{water} at 5,000 feet deep = 62.4 x 5,000 = 312,000 psf = 2,167 psi (pounds per square inch)

P_{oil} at 5,000 feet deep = 51.16 x 5,000 = 255,800 psf = 1,776 psi (pounds per square inch)

When the well was in operation before the platform burned and the 21” pipe collapsed to the ocean floor the system also had the pressure of the reservoir on it. We will call this additional pressure P_{reservoir.}

The pressure inside the pipe at the location of the oil well outlet from the ground = P_{reservoir }+ P_{oil }, and outside the pipe we have P_{water }. The only unknown is P_{reservoir }and we are going to find out what the maximum value is for this number from the forensic evidence that we have.

We start this investigation by analyzing a similar pipe 21 inches in diameter and with a thickness of ½ inch. We use a pipe made of structural steel A500 Grade C. See http://www.steeltubeinstitute.org/pdf/brochures/producers_capabilities.pdf

for the round steel pipe. From the Manual of Steel Construction of the AISC we obtain the following data.

F_{y} (minimum yield stress) = 50,000 psi

F_{u} (minimum tensile stress) = 62,000 psi

These are the highest values for steel stress of round pipes.

If we take this pipe and pressure test a piece about 20 feet long until it breaks we can expect to see a bulging of the walls and a burst or explosion making a hole at some point in the pipe.

This kind of pressure failure is caused by concentric ring stress applied from the inside out. Concentric failure can also occur by crushing in, if the pressure is applied on an empty pipe from the outside.

Another type of pipe failure is bending. If you sit this pipe 20’ long at the ends and apply a concentrated load at the center perpendicular to the pipe this pipe will break at the middle. To illustrate this failure take a straw and hold it at the ends and bend it at the middle and see how it breaks.

This type of failure is the one seen in the videos of the pipe that resulted from the pipe bending from its weight when it fell to the bottom of the ocean just after it lost its anchor at the oil well platform. Think of a building two and a half times taller than the twin towers collapsing on its side.

To further support this assumption let us analyze next the flow of oil shown on the videos of the broken pipe.

Think of a pool that has a filtering system and the outlets that re-circulate the water back in, the flow is defined and laminar and it displaces the water in the pool. If we increase the pressure of the pipe the displacement will reach a longer distance and we would be able to feel the pressure at a farther distance.

What we observe at the break of the pipe videos is the oil diffusing into the water and not shooting out for a big distance before diffusing. This implies that the difference in pressure from the oil inside the pipe to the water outside is not very big.

Now we are going to get a little more technical but I will try my best to explain in terms that you can understand and scientific enough so that other engineers can follow also.

To determine the pressure under which this 20 foot long test pipe would fail we use a technical reference by T.Y. Lin from his book Design of Prestress Concrete Structures Cpyright 1955, 1963 by John Wiley & Sons, Inc. to get an equation of wall tension in a cylindrical structure with pressure applied at the inside.

The formula for circular ring force in cylindrical surfaces is given by a very simple formula:

T = Rp

T = tensile force in a ring section

R = internal radius of pipe

p = internal pressure of pipe

Solving for the unknown p:

p = T / R

We must find T to solve the above equation, and this is easy to do. Let us take a piece of ½” thick pipe, 1” long and figure the cross sectional area. Think of a wedding ring cut in half or see drawing.

A_{pipe} = 0.5 x 1 = 0.5 in^{2} (square inches)

T = A_{pipe }x F_{u} = 0.5 x 62,000 = 31,000 # (pounds)

R = 10 inches

So:

p = T / R = 31,000 / 10 = **3,100 psi**

With this information we can find the maximum pressure that could have been in this pipe. If the pipe would have failed in a pressure mode there would have been no way of determining the maximum pressure using this procedure due to the fact that any internal pressure above 3,100 psi would have exploded the pipe.

Fortunately that is not the case and we can use this number in the design of our containment caisson. We can also use this number to find the maximum pressure that is in the reservoir of oil.

Now let us understand a little more about pressure inside the pipe. The pipe starts at the reservoir of oil and went up to the surface of the ocean. Each point along this whole length of 35,000 feet has a different pressure. We will start our investigation at the bottom of the well in the bottom of the ocean.

At this point the pipe before the accident had a pressure that was bigger than the pressure outside the pipe and the oil was contained. Now let us do the numbers to find the maximum pressure that the pipe can take at this point. P_{reservoir }is the reservoir pressure at the bottom of the sea.

P_{reservoir at the bottom of sea }+ P_{oil }– P_{water }= p = 3,100 psi

P_{reservoir at the bottom of sea} = 3,100 – P_{oil }+ P_{water }= 3,100 – 1,776 + 2,167 = 3,491 psi

Now the maximum pressure inside the reservoir at 30,000 feet below the ocean floor can be found

P_{reservoir at the bottom of the earth }=_{ }P_{oil on earth pipe }+ P_{reservoir at the bottom of sea }= 30,000 x 51.16 / 144 + 3,491

P_{reservoir at the bottom of the earth }= 10,658 psi + 3,491 psi = **14,149 psi**

This value is bigger due to the fact that the oil pressure must overcome friction from the walls of the pipe to get up the whole 30,000 feet, but for our discussion and design this refinement is not needed.

**Design of caisson containment structure **

With the pipe full of oil above the blowout preventer removed there is a column of oil 5,000 feet high that was replaced with a column of water 5,000 feet high, so let us reduce the pressure by the difference between oil and water pressures.

P_{reservoir at the bottom of sea }= 3,100 – (2,167 – 1,776) = **2,709 psi** (no pipe above well, present condition)

It is important to understand that the above number is a maximum based on my forensic engineering site investigation. The actual existing pressure may be a lot smaller. The design is going to be based on this number with a factor of safety of 1.2.

Factor of Safety F.S. = 1.2

P_{reservoir at the bottom of sea} x FS = 2,709 x 1.2 = 3,250 psi

Area of cavity ceiling inside the caisson A_{ceiling} = πR^{2} = 3.1416 x 6.5^{2} = 133 ft^{2} = 19,113 in^{2}

Force from oil pressure pushing caisson up = 3,250 x 19,113 = 62,117,250 #

To counteract this force I am using the pressure of the water above the caisson that is pushing down. For this force to act on the caisson the walls of the caisson must be bearing at the ocean floor so that no water or oil pressures are acting there to push up. Find the Area required to accomplish this force balance.

A_{wp} = πR^{2}

Solving for R

R = √ A_{wp} / π = 123 inches = 10.3 ft **use 10 ft**

** **

A steel plate used at the bottom of the caisson is there to prevent the flow of oil from going out

from the inner chamber of the caisson or water from coming in.

Now if BP was able to place a very small cap to partially reduce the flow of oil the question that begs asking is what kind of pressure is there going out that would allow the cap to be placed on top. Think of a fire hose going full blast and somebody with a cap trying to shut it off.

It is obvious that further forensic engineering is required in this problem. A video of the full length of pipe should be made and then the collapsed pipe taken out and forensically studied.

The same can be said of the burned oil platform. Videos can tell a significant story to trained observers.

As a further safety factor against exceeding pressure the concrete weight of the caisson is 1,465,000 pounds. This weight divided by the surface area of the ceiling inside translates to an additional 77 psi of pressure acting against the oil well. This means that when the design pressure is exceeded by 77 psi the caisson will lift up letting the oil escape relieving the pressure. Think of the pressure cooker in your kitchen and the steel safety valve that starts hissing when the pressure rises.