Effective Producing Time (tc)

Effective producing time is based on the Horner time theory and is defined as the flow period prior to shut-in at a constant rate. In reality, the flow prior to shut-in is not at a constant rate, but varies. Essentially, effective producing time transforms the duration of the variable rate drawdown period to the duration it would have been, if the flow rate had been constant. It uses material balance principles and is defined as follows:

Effective producing time is only valid if the final flow rate before shut-in is constant. If this is not the case, superposition time, which is more rigorous but also much more computationally intensive, must be used.

Effective producing time has been called a number of different names (some of them misnomers) in literature. Some common aliases for effective producing time include:

• Producing Time (tp)
• Corrected Time (tc)
• Corrected Producing Time
• Horner Time
• Flow Time
• Equivalent Producing Time
• Material Balance Time