02.Productivity Index

02.Productivity Index

Productivity index  (PI) or (J) is a parameter which gives us information about the duration expected for the recovery and the performance of the well , productivity index forms a straight line .

Evinger & muskat pointed out that the straight line of  PI is only applicable when we deal with single phase flow .and the equation would be :

For the multi  phase flow we should figure out how to estimate the performance because the PI is not any more linear , in this case we have several methods which are based on empirical relationships that are used in predicting oil performance but the most used are    :

1.    Vogel’s inflow performance relationship :

This method is based on computer simulation results and the empirical relationship is given by: 

                    P_wf : bottom hole pressure is determined from production test.

           P_r average : is an estimation of the average pressure on the reservoir.

 

    2.    Fectovich  inflow performance relationship :

  it is based on empirical relationship too which is :

  

 It requires a multiple  rate tests by doing isochronal test  to estimate C & n , the precedent relationship could be rearranged and it gives us :

We exposed only two methods in this article , but other methods are available  such as standing’s,wiggins,the klin klark methods .

Gallice & wiggins compared between methods and provide us information  about advantage & disadvantage  for each method  also they provide us information by answering the following questions:

-         what is the best method to use in a specific circumstance ?

-         what are the advantages of every method?

-         What are the limits for every method?