4. Read the first part of the text and find English equivalents for the given words and expressions:

cильно измениться; трудный и неэффективный; точные методы обнаружения; геологическая разведка; в форме купола; изучая и составляя карты поверхности; сейсмические волны; различным образом взаимодействует; отражаться; тысячи футов ниже морского дна; чувствительное оборудование; разведочная скважина; различные слои породы; неблагоприятные условия.

The practice of locating natural gas and petroleum deposits has been transformed dramatically in the last 20 years with the help of extremely advanced technology. In the early days of the industry, the only way of locating underground petroleum and natural gas deposits was to search for surface evidence of these underground formations. Oilmen had to scour the earth, looking for seepages of oil or gas emitted from underground before they had any clue that there were deposits underneath. However, exploration process was very inefficient and difficult because of a low proportion of petroleum and natural gas deposits that actually seep to the surface. And the necessity for more accurate methods of locating these deposits has increased.

Geological Surveys. Exploration for natural gas typically begins when geologists examine the surface structure of the earth, and determine areas where it is geologically likely that petroleum or gas deposits might exist. It was discovered in the mid 1800s that ‘anticlinal slopes’ (the areas where the earth is forming the dome shape) are characterised by a great number of reservoirs. By surveying and mapping the surface and sub-surface characteristics of a certain area, the geologist can define which areas are most likely to contain a petroleum or natural gas reservoir.

S eismic Exploration. As the Earth's crust is composed of different layers, each with its own properties, seismic waves traveling underground interacts differently with each of these layers. These seismic waves, emitted from a source, will be reflected back toward the source by the different underground layers. Through seismology, geophysicists are able to artificially create vibrations on the surface and record how these vibrations are reflected back to the surface, revealing the properties of the geology beneath.

Offshore Seismology. A slightly different method of seismic exploration is used when exploring for natural gas that may exist thousands of feet below the seabed floor. Instead of trucks and geophones, a ship is used to pick up the seismic data and hydrophones are used to pick up seismic waves underwater. These hydrophones are towed behind the ship in various configurations depending on the needs of the geophysicist. Instead of using dynamite or impacts on the seabed floor, the seismic ship uses a large air gun, which releases bursts of compressed air under the water, creating seismic waves that can travel through the Earth's crust and generate the seismic reflections that are necessary.

M agnetometers. Magnetic properties of underground formations can be measured to generate geological and geophysical data. This is accomplished through the use of magnetometers, which are devices that can measure the small differences in the Earth's magnetic field. In the early days of magnetometers, the devices were large and bulky, and only able to survey a small area at a time.

Gravimeters. Geophysicists can also measure and record the difference in the Earth's gravitational field to gain a better understanding of what is underground. Different underground formations and rock types all have a slightly different effect on the gravitational field that surrounds the Earth. By measuring these minute differences with very sensitive equipment, geophysicists are able to analyze underground formations and develop clearer insight into the types of formations that may lie below ground, and whether or not the formations have the potential for containing hydrocarbons like natural gas.

E xploratory Wells. The best way to understand a subsurface geology and the potential for natural gas deposits is to drill an exploratory well. It consists of digging into the Earth's crust to study the composition of the underground rock layers in detail. Geologists also examine the drill cuttings and fluids to gain a better understanding of the geologic features of the area. Drilling an exploratory well is an expensive, time consuming effort. Therefore, exploratory wells are only drilled in areas where other data has indicated a high probability of petroleum formations.

Logging. Logging refers to performing tests during or after the drilling process to allow geologists and drill operators to monitor the progress of the well drilling and to gain a clearer picture of subsurface formations. There are many different types of logging, in fact; over 100 different logging tests can be performed. They consist of a variety of tests that illuminate the true composition and characteristics of the different layers of rock that the well passes through. Logging is also essential during the drilling process. Monitoring logs can ensure that the correct drilling equipment is used and that drilling is not continued if unfavorable conditions develop.

Various types of tests include standard, electric, acoustic, radioactivity, density, induction, caliper, directional and nuclear logging, to name but a few. Two of the most prolific and often performed tests include standard logging and electric logging.