Every year, thousands of students finish their master thesis at NTNU in Trondheim. However, most of this work will never be read by anyone, except by their supervisor and their examiner. What a waste?!

From the great comic: Piled Higher and Deeper

I have thought about writing something about the work I've done for the past year. It was my girlfriend who finally made up my mind. She told me that in her master thesis a part of the work would be to convey knowledge on her subject to high-school students. She feels that this should be a part of all academical work. One way to accomplish this could be writing an abstract of the thesis using simpler terms, and avoiding difficult topics. NTNU could then host these abstracts on a website where high-school students who are interested could browse and read them.

To test this I'm going to try to write a short text about my master thesis. It should be easy to read and follow, and not too long. Perhaps the student should make a poster, that introduces and explains his / her work. This is often done during PhD work. After all, why should all the time and work we spend on our thesis mainly go to waste? Could it not at least be a motivation to young students who wonder what a master thesis typically is about.

My background

During the last year of a master of science degree at NTNU all students are required to write a project work, and a master thesis. Since I had been involved with Weatherford Laboratories for a couple of years it was natural that I wanted to write my thesis for them. My project work covered a lot of the theory and methods that we use, and also proposed some improvements. It also covered an entirely new technique, that I unfortunately had to conclude was not suitable for us. I had thought that implementing this technique would be my master thesis, but now we had to come up with something else.

Weatherford Laboratories specializes in reservoir core sample analysis. The core samples are drilled up from oil reservoirs and shipped to our laboratories in Trondheim. There several tests can be conducted to characterize these cores. In the end the results we find will help oil companies make decisions, such as whether an oil field is worth developing, or how many wells are necessary.

One important result is a relative permeability curveSchlumberger - relative permeability. In order to determine this curve we must find the saturation in the cores, and we do this using radiation. This is where I enter the story. My specialty is nuclear physics, radiation and radiation safety. The field is quite advanced, and usually people frown and give up when they hear about it.

I will now try to present my work in a fashion that I hope will be interesting to a person not familiar with oil reservoirs, radiation physics or instrumentation. It should be short and concise, but still true to the the thesis itself.

A better way to measure saturation

In my master thesis I describe a better way to measure the saturation in core samples from oil reservoirs. The method I propose is faster, and should give a better result then the current method. Experiments show that the new method works well.

Introduction

Everyone today knows that oil means big money. Oil gives petroleum, and petroleum is of importance to the maintenance of industrialized civilization itself. The amount of petroleum consumed on Earth each year is simply staggering. In 2008 we used 85462000 barrels of petroleum each dayWorld oil consumption. It takes about two liters of crude oil to make one liter of petroleumU.S. Energy information. To put this into perspective, if you filled a soccer field (105 x 68 meters) with the amount of crude oil consumed each year it would make a 1400km high pillar of oil. An incomprehensible amount.

The amount of crude oil consumed globally has steadily increased, but the number of large oil finds has decreased. It seems like most of the larger, and most profitable reservoirs have already been found. This is a problem for the oil companies, since a small oil field gives a small margin between making and loosing money. They need to make sure that the process from finding a potential field, through producing it, and finally cleaning up and finalizing it, goes exactly as planned and budgeted. In order to do this they need to know a lot about the reservoir rock and fluids.

Reservoir engineering

The best way to learn about the reservoir is to do a test drill. This is a very expensive test, but still much cheaper than hoping there is oil and starting production. They drill into the reservoir rock, and bring back up core samples. These samples are then shipped to special core analysis laboratories across the world. By doing experiments on these small samples we can imagine doing experiments on the whole reservoir.

I often think of oil reservoirs as a sponge. The sponge material itself is the reservoir, mostly rock and clay. The rock is not entirely solid, there is pores inside, connected like a miniature system of caverns. The reservoir rock contains oil, like the sponge contain water. You have to apply pressure to a sponge to get the water out, much like an oil reservoir, except that they already are at high pressure. So if we imagine that our sponge is an oil reservoir, what properties of the sponge are important when it comes to getting the most water out of it?

The water in the sponge is located in the pores of the sponge, so the larger pores the more water, see the figure below. Further, if the sponge itself is big, it can hold more water. If we apply a large pressure, more water will be squeezed out. We can also imagine that the pores inside the sponge can hinder the water flow to a certain degree, and that this can vary with different kinds of sponge. It is this ability for oil to flow in the reservoir rock that we try to determine at Weatherford Laboratories. The property is known as permeability. In latin, permea simply translates into: to pass through, so we measure the ability of oil to pass through the reservoir rock. If permeability is high, it is easy to get a lot of oil out of the reservoir.

We would like to report the permeability at different saturations. Saturation is simply how much oil is there inside the rock. When you hold a sponge under water it is completely saturated, but if you wring it and leave it to dry, it will be completely un-saturated. So how can we know how much oil there is inside a core sample at any time, without breaking it apart, or ruining the core? We use radiation to look into the core itself.

Gamma radiation

You can imagine that radiation is very small particles, flying at high speed in a straight line. Whenever it comes into contact with material there is a certain chance it will simply disappear, or be scattered away. This chance will strongly depend on the material that the particles are passing through. If you send a thousand gamma particles through a bottle filled with pure water, perhaps 200 will come out on the other side. Oil however has a smaller chance of stopping the radiation, so if you repeat the experiment with a bottle of clean oil, perhaps 500 particles will come out on the other side.

If we can imagine a mix of oil and water in the bottle, even though oil and water doesn't mix, then we could say that the number of surviving particles would have to be between 200 and 500. This is simply because it is no longer completely saturated with either oil or water, so it must lie in between. Say we measured 346 particles on the other side of the bottle, using this number we could calculate exactly how much oil and water there was in the bottle. This is how we determine the saturation of oil and water inside the reservoir core samples.

I have improved this method by reducing the time it takes to do this experiment, simply by finding a way to avoid some of the measurements. Normally when you do fewer measurements, you will loose data. This will often lead to a lower accuracy, and this is of course not acceptable. By determining some important properties of the fluid, I can save time without loosing information about the saturation. In the industry, time is money, and saving time is of great value.

My method can easily be tested, and through experiments we have shown that it works to a good degree of accuracy. There is still some further work needed to be able to use it during projects, but I hope it will be used in the future.

This quickly became a long text, but I think most of it was necessary to cover the background, in order to motivate my work. I did however not touch on what exactly I'm doing, since I could not figure out a way to really formulate it, without using another page to describe the equipment, methods and formulas. I think many students will find it equally hard to convey what they are really doing, because it is very difficult to say it easily with few words.

If you are writing (or have written) a thesis, try it yourself: write a short text, explaining what your thesis is about, that you think a high-school student would understand and find interesting. I would like to see some good examples.