Steve Gardner, Age 11, Of Greensburg, Ky., for his question:

How do they know where to drill for oil?

A new method to detect buried petroleum is always welcome. Last month, still Another gadget was put to work to help the experts in the endless search for oil in The ground. It will add data to the facts already gathered by surveys and geological tests. But with all this information, the best oilman can only guess where pctroleum is buried.
A pool of oil may rest three miles below the surface of the ground. To prove the oil is there and get it out, the oilman must reach it by drilling a hole. This operation may cost $500,000 and far more if the oil is deep. Probing for petroleum     Is expensive, and the oilman tries to find the likely places before he starts to drill. Geologists survey whole continents t0 find the places where oil is likely to be and where it is not likely to be. Their charts show where shallow seas once swamped the land, for oil tended to form under these conditions. Petroleum is found in layers of sandstone, limestone and other porous, sedimentary rocks formed underwater.
When the pores of a thick layer of sedimentary rock are saturated with oil, we have a pool of petroleum. The reservoir of buried petroleum must be held in place by denser rocks below and on the sides. It must have a roof of dense, solid rock to prevent it from seeping to the surface. When these conditions are met, the oilman may decide to drill. But of nine drillings, only one is likely to yield a worthwhile supply.
The expert uses instruments to form a picture of the buried rocks and their formations. A gravity meter reveals the formations of dense and light rocks below Ground. A magnetometer reveals buried lavas which are not likely to contain oil. An underground explosion may be used to create a small earthquake. Its vibrations reveal the densities of buried rocks.
When all the data suggests a likely spot, the expert starts to drill for oil. As the drill bites down, it brings up samples for testing. These cores of rock show When the drill is nearing petroleum. If they are poor, they show that drilling is useless and the work stops. A new tv gadget may be used to spy down the drill hole. It provides more data to tell the oilman whether it is worthwhile to go on drilling.
The oilman's tv instrument can spy a mile down into the earth. One camera is trained on the bottom of the hole while another scans the walls. It shows the minerals and. Formations where oil is or is not likely to occur. With surveys and other tests this instrument will make it a little easier for the oilman to know where to drill. But with all this help, he cannot be certain until his drill reaches the buried pool and a dark, oily fountain of petroleum gushes up with a gush to the surface.