What Instruments Do They

The first step in exploring for oil is taken by the geologist who looks for outcropping of sandstone or other oil-bearing rock. Some­times he finds them by consulting aerial maps made from photographs taken from planes; sometimes he uses state geological maps, and sometimes he examines samples of various strata called " cores", which have been brought up inside drill pipes from wells already dug.

An oil-exploring party usually begins by carefully mapping and investigating the countryside. A field geologist and his driver pack up after a day's work of surveying in the desert.

Chapter Two

When geologists find a likely spot, experts called geophysicists are called in. With their instruments they try to get a clearer picture of what the drillers may expect to find hundreds, sometimes thou­sands, of feet beneath the surface. To do this they use three different kinds of instruments: the gravimeter, the magnetometer, and the seis­mograph.

Exploring for Petroleum

The gravimeter, a very delicate instrument, measures the pull of the earth's gravity, which varies slightly from one spot to anbtKer". For instance, you would weigh a tiny bit more while standing on a ledge of heavy granite than if you were on soft rock like sandstone. This minute variation is measured by the gravimeter and tells the ex­pert something of what lies below.

The magnitometer electrically measures variations in the earth's magnetic field caused by different kinds of rocks below the surface.

The seismograph used by oil men is the same as the one which records earthquakes. The geophysicist sets off a charge of dynamite in a small hole. From this, sound waves travel downward until they strike a layer of rock which reflects them back to the surface. Here they are recorded by geophones. By noting the time it takes to travel from the explosion to the rock and back again to the surface, the expert can tell what kind of rock lies below and how far down it is.

Still another way to pry into the earth's secrets is to drill a small hole with a rotating drill bit at the end of a long pipe. Electrical meters connected with the bit measure the resistance of different kinds of rock to the current.

Cores are studied by a paleontologist, an expert on ancient fos­sils. He can tell by the types of fossils how old the rock formation is.

In spite of all their painstaking work and study, geologists, geo-physicists, and paleontologists can tell only where the conditions indi­cate that oil might be found.