Borehole Logging Techniques for Reservoir Characterization

This book deals with the part of formation evaluation known as well logging. Well logs are a record versus depth of some physical parameter of the formation. Parameters such as electrical resistance, naturally occurring radioactivity, or hydrogen content may be measured so that important producing characteristics such as porosity, water saturation, pay thickness, and lithology may be determined. Logging instruments (called sondes) are lowered down the borehole on armored electrical cable (called a wireline). Readings are taken while the tool is being raised up the hole. The information is transmitted uphole via the cable where it is processed by an on-board computer and recorded on magnetic tape and photographic film. In older logging units, downhole signals are processed by analog circuits before being recorded.