Well Log Basics

Abstract

The late George R. Pickett of the Colorado School of Mines once said that using well logs in oil and gas exploration was “like hunting on a game preserve.” To some this may be a revelation. However, most people in the petroleum industry know that well logs play a key role in oil and gas exploration and reservoir evaluation. When a well drilling is finished, a decision must be made as to whether to complete the well or plug and abandon it. Well logs often provide the data that help make the correct decision. Well logs can sometimes be used to identify the presence of hydrocarbons where the quality of the reservoir rock is so good that nearly all traces of hydrocarbons have been flushed from the drilling cuttings circulated to the surface by the drilling fluid. It is a paradox that the best hydrocarbon “shows” occur in the poorer reservoir rocks, whereas the poorer shows occur in the best reservoir rocks. Well logs can be used to identify the best reservoirs.