Changes

[[file:quick-look-lithology-from-logs_fig1.png|thumb|300px|{{figure number|1}}Characteristic log shapes for different types of sand bodies set in shale, (a) Funnel shape, coarsening upward. Note that this is the shallowest interval, so the shale is least compacted. (b) Cylinder shape, blocky. Note that the SP log is featureless because the borehole salinity is the same as formation salinity. (c) Bell shape, fining upward. Note that coal is present in addition to shale.]]

[[file:quick-look-lithology-from-logs_fig1.png|thumb|300px|{{figure number|1}}Characteristic log shapes for different types of sand bodies set in shale, (a) Funnel shape, coarsening upward. Note that this is the shallowest interval, so the shale is least compacted. (b) Cylinder shape, blocky. Note that the SP log is featureless because the borehole salinity is the same as formation salinity. (c) Bell shape, fining upward. Note that coal is present in addition to shale.]]

The shape of a gamma ray (or SP) log through a sand body is often thought of as a grain size profile. Three basic log shapes are recognized: funnel (coarsening upward), cylinder (blocky), and bell (fining upward) ([[:file:quick-look-lithology-from-logs_fig1.png|Figure 1]]). These three shapes can be subdivided into smooth (relatively homogeneous) or serrate (with interbedded thin shales).

The shape of a gamma ray (or SP) log through a sand body is often thought of as a [[grain size]] profile. Three basic log shapes are recognized: funnel (coarsening upward), cylinder (blocky), and bell (fining upward) ([[:file:quick-look-lithology-from-logs_fig1.png|Figure 1]]). These three shapes can be subdivided into smooth (relatively homogeneous) or serrate (with interbedded thin shales).

Log shapes typically reflect changing depositional energy from high (clean, coarser sand) to low (shaly, finer sand). An interpretive jump is usually made from depositional energy to depositional process and hence depositional environment. Often this jump is made without seriously considering the intermediate steps. This can be dangerous. Each of the steps is highly ambiguous and must be augmented by other evidence, such as unit thickness, associated rock types, and overall depositional setting. Typically,

Log shapes typically reflect changing depositional energy from high (clean, coarser sand) to low (shaly, finer sand). An interpretive jump is usually made from depositional energy to depositional process and hence depositional environment. Often this jump is made without seriously considering the intermediate steps. This can be dangerous. Each of the steps is highly ambiguous and must be augmented by other evidence, such as unit thickness, associated rock types, and overall depositional setting. Typically,