Here's a demonstration of how this works. Not all liquids are the same. Some are thin and flow easily. Others are thick and gooey. A liquid's resistance to flowing is called its viscosity.
Viscosity is an important property of drilling fluids.
One way to test the viscosity of a liquid is to drop something into it and see how long it takes to sink. This article on drilling fluids touches on topics in history, drilling technology, physics and environmental sciences. This ship is one of the largest and best outfitted scientific vessel for marine geology in the world. It carries sophisticated equipment for drilling into the sea floor to collect samples, and it houses a laboratory where an international group of scientists analyze these samples. This article provides an overview of how oil was created over the past several hundred million years, and how it is recovered for our use.