2. n. [Reservoir Characterization]
A two-point statistical function that describes the increasing differences or decreasing correlation, or continuity, between sample values as separation between them increases. The term variogram is sometimes used incorrectly in place of semivariogram. The two differ only in that the semivariogram uses each pair of data elements only once, whereas the variogram uses all possible data pairs. Semivariograms are usually used instead of variograms, but opposite vector directions (for example, north and south) are recognized as representing the same thing and having identical ranges, sills, nugget points and the like.