Seismic Technology: How It Works

Julia Baggs, Chevron Energy Technology Company

Hi, my name is Julia Baggs and I work at Chevron on a team that explores the earth for oil and natural gas. Today, we’re going to talk about how we use technology to aid us in the search for oil and natural gas deep beneath the surface of the earth.

Oil and natural gas are normally found in what we call reservoir rocks. These are rocks, including sandstone, that are uniquely suited to hold oil and natural gas between each of the grains of sand in the rock. There’re all these little pore spaces, kind of like the pores in your skin, or in a sponge, that can hold onto these little tiny molecules.

To find the reservoirs, we use seismic technology. We can send sound waves deep into the earth and listen to them when they bounce back up using little, tiny things called geophones. They’re basically electronic ears that record a signal when they hear the sound come back. The signal that we get out of them actually looks like this. It looks like a squiggle. If we put thousands of these squiggles together in a line, then we have a slice or a cross section of the earth that we can actually see structures in.

After we collect the seismic data, we assign a team of highly educated, technically skilled geologists, geophysicists, reservoir engineers, to interpret the data, to decide where the different formations are underground, where there are structures that would be conducive to holding reservoirs of oil and natural gas.

After our teams have done their work, then it’s time to drill the exploration well. A success rate of 50 per cent in finding oil or natural gas in that well is actually really good in our industry. Because, after all, the data is just a representation of what’s beneath the surface. But we don’t know what’s really down there until we drill that well.

Well, that’s an overview of how we search for oil and natural gas.

Memorize the words:

to aid – допомагати search – пошук reservoir – колектор (нафти, газу) suited – підхожий, придатний to hold – тримати, утримувати sponge – губка sound waves – звукові хвилі to bounce – відскакувати geophone -- геофон (сейсмоприймач) squiggle – сейсмічна траса, записана способом відхилень slice – скибка cross section – розріз to assign – призначати skilled – кваліфікований, майстерний conducive – сприятливий to drill – бурити exploration well – розвідувальна свердловина overview – огляд, загальне уявлення

 

Answer the questions:

5. What is the Chevron Company engaged in?

6. Where are oil and natural gas found?

7. What technology does the Chevron Company use in the search for oil and natural gas?

8. What kind of waves do they use?

9. What do they do after collecting seismic data?

10. Who interprets the data?

11. When is it time to drill the exploration well?

12. What success rate is considered good in this industry? Why?

Magnetometers

A magnetometer is a measuring instrument used to measure the strength and, in some cases, the direction of magnetic fields. Magnetometers can be divided into scalar devices which only measure the intensity of the field and vector devices which also measure the direction of the field. Magnetometers are widely used for measuring the Earth's magnetic field and in geophysical surveys to detect magnetic anomalies of various types.

 

Helium Vector Magnetometer (HVM) of the Pioneer 10 and 11 spacecraft

Memorize the words:

strength – сила case – випадок direction – напрям scalar – скалярний device – пристрій, винахід vector – вектор(ний) intensity – напруженість, інтенсивність survey – дослідження detect – виявляти, відкривати

Answer the questions:

1. What are magnetometers used for?

2. What do scalar magnetometers measure?

3. What can be measured with vector magnetometers?

Early magnetometers

The first magnetometer was invented by Carl Friedrich Gauss in 1833 and notable developments in the 19th century included the Hall Effect which is still widely used.

In 1833, Carl Friedrich Gauss, head of the Geomagnetic Observatory in Gottingen, published a paper on measurement of the Earth's magnetic field. It described a new instrument that consisted of a permanent bar magnet suspended horizontally from a gold fibre. The difference in the oscillations when the bar was magnetised and when it was demagnetised allowed Gauss to calculate an absolute value for the strength of the Earth's magnetic field. A magnetometer may also be called a gaussmeter. The gauss, the CGS unit of magnetic flux density was named in his honour, defined as one maxwell per square centimetre; it equals 1×10⁻⁴ teslas (the SI unit).

Coast and Geodetic Survey Magnetometer No. 18, used in the magnetic survey of Maryland conducted in the 1890s

Memorize the words:

Hall effect – ефект Холла – The production of a potential difference across an electrical conductor when a magnetic field is applied in a direction perpendicular to that of the flow of current. Named after Edwin H. Hall (1855 - 1938), American physicist.

notable – видатний, значний development – поліпшення, вдосконалення permanent – постійний bar – стрижень suspend – підвішувати fibre – нитка oscillation – коливання value – цінність, значення CGS – від centimetre-gram-second система СГС, сантиметр-грам-секунда unit – одиниця flux – потік maxwell – максвел (одиниця вимірювання магнітного потоку) tesla – тесла (одиниця вимірювання магнітної індукції) SI – the international system of units of measurement Міжнародна система одиниць, СІ equal – дорівнювати

Answer the questions:

1. Who and when invented the first magnetometer?

2. What was Carl Friedrich Gauss?

3. What did Gauss’ instrument consist of?

4. What allowed Gauss to calculate an absolute value for the strength of the Earth's magnetic field?

5. What is gauss?

 

Gauss Karl Friedrich (1777 - 1855), German mathematician, astronomer, and physicist. He laid the foundations of number theory.

Faraday Michael (1791 - 1867), English physicist and chemist. He contributed significantly to the study of electromagnetism and discovered the laws of electrolysis.

Kelvin William Thomson, 1st Baron (1824 - 1907), British physicist and natural philosopher. He introduced the absolute scale of temperature and restated the second law of thermodynamics. He was involved in the laying of the first Atlantic cable, for which he invented several instruments.

Maxwell James Clerk (1831 - 79), Scottish physicist. He extended the ideas of Faraday and Kelvin with his equations of electromagnetism, and he succeeded in unifying electricity and magnetism, identifying the electromagnetic nature of light and postulating the existence of other electromagnetic radiation.

Gravimeter

An Autograv CG-5 gravimeter being operated

A gravimeter is an instrument used in Gravimetry for measuring the local gravitational field of the Earth. A gravimeter is a type of accelerometer, specialized for measuring the constant downward acceleration of gravity, which varies by about 0.5% over the surface of the Earth. Though the essential principle of design is the same as in other accelerometers, gravimeters are typically designed to be much more sensitive in order to measure very tiny fractional changes within the Earth's gravity of 1 g, caused by nearby geologic structures or the shape of the Earth. Gravimeters display their measurements in units of gals (cm/s²), instead of more common units of acceleration.

Gravimeters are used for petroleum and mineral prospecting, seismology, geodesy, geophysical surveys and other geophysical research, and for metrology.

There are two types of gravimeters: relative and absolute. Absolute gravimeters measure the local gravity in absolute units, gals. Relative gravimeters compare the value of gravity at one point with another. They must be calibrated at a location where the gravity is known accurately, and then transported to the location where the gravity is to be measured. They measure the ratio of the gravity at the two points.

Memorize the words:

vary – мінятися, змінюватися though – однак, проте essential – істотний design – конструкція, проектувати sensitive – чутливий tiny – крихітний fractional – дробовий, частковий relative – відносний, порівняльний compare – порівнювати value – значення, величина calibrate – калібрувати, градуювати accurately – точно location – місце ratio – пропорція, співвідношення

Answer the questions:

What is a gravimeter?