Not so very long ago, after several decades of robust production, U.S. crude oil output was in a sharp decline as the country’s accessible oil reserves were being depleted. The U.S. was rapidly becoming increasingly dependent on foreign oil. At the same time, supplies of natural gas also were vanishing. Thanks to scientific discovery and innovation in drilling techniques, all that has changed. Dramatically. But to grasp the significance of America’s changing energy picture, it helps to understand where these valuable resources come from, where they exist today and how we unlock them from deep below the earth’s surface.
Conventional production & vertical drilling
Drilling for oil in America dates to the mid-1800s, first in Pennsylvania and later in Texas and eventually in many other states. But the methods for drilling have changed dramatically over time. Oil traditionally was produced from reservoirs using vertical drilling to a target directly below the drill site, and pulverized rock (drill cuttings) was brought to the surface by injecting a mixture of mud and water down a hollow drill pipe to a rotary bit. As the hole deepened, additional lengths of drill pipe were added. When certain depths were reached, casing (steel pipe that forms the walls of the well) was put into the hole to stabilize it and then cemented into place. Drilling resumed, with progressively smaller diameter layers of steel casing inserted as the well became deeper. In addition to stabilizing the well hole, these layers of casing also acted as barriers between freshwater aquifers and the material that would be used in the drilling process as well as the oil and gas the well would produce.
Once the desired vertical depth was reached, the drill pipe was removed and sophisticated tools were used by geologists to analyze the rock in the well to evaluate the existence of possible oil and gas deposits in the wellbore (the hole drilled by the bit). Based on their findings, the exploration companies decided whether to invest the additional capital to complete the well or plug and abandon the well. If the decision was made to complete the well, additional pipe was run to the bottom of the well and cemented in place.