1. n. [Geology, Shale Gas]

The concentration of organic material in source rocks as represented by the weight percent of organic carbon. A value of approximately 0.5% total organic carbon by weight percent is considered the minimum for an effective source rock, although values of 2% are considered the minimum for shale gas reservoirs; values exceeding 10% exist, although some geoscientists assert that high total organic carbon values indicate the possibility of kerogen filling pore space rather than other forms of hydrocarbons. Total organic carbon is measured from 1-g samples of pulverized rock that are combusted and converted to CO or CO2. If a sample appears to contain sufficient total organic carbon to generate hydrocarbons, it may be subjected to pyrolysis.

Alternate Form: total organic carbon

2. n. [Drilling]

Abbreviation for "top of cement." The highest depth of set cement in the annulus after well cementing, generally determined from logging. Although cementing engineers calculate the expected top of cement before pumping, unanticipated washouts or losses to the formation can affect the final height of the cement column.

See: lost circulation,  circulation loss,  natural fracture,  bump the plug,  cement bond log