The average size of the training arena D50 is usually estimated by sieve size analysis of samples obtained sand from:
* conventional core samples
* wall core samples.
* Samples obtained by dewatering.
* Samples produced.
Of these, the most representative training samples are those obtained from conventional core, however, are not easily accessible due to the cost of making core operations.
When there is no formation sand samples, approximates the average size value of training through Coberly5 equations, Blick and Civan6: