Definition

WFP – Well Performance Analysis analysis is a comparative analysis between:

• the formation fluid deliverability (the ability of reservoir to produce or take-in the fluid) which is called Inflow Performance Relation (IPR)

and

• wellbore fluid deliverability (the ability of well to lift up or lift down the fluid) and which is called Vertical Flow Performance (VFP) or Tubing Performance Relation (TPR)

It is based on correlation between surface flowrate  $//<![CDATA[ \begin{array}{l}q\end{array} //]]>$ and bottomhole pressure  $//<![CDATA[ \begin{array}{l}p_{wf}\end{array} //]]>$ as a function of tubing-head pressure  $//<![CDATA[ \begin{array}{l}p_s\end{array} //]]>$ and formation pressure $//<![CDATA[ \begin{array}{l}p_R\end{array} //]]>$ and current reservoir saturation.

Application

• Setting up the required production or injection regime for each well upon the current formation pressure, reservoir saturation and production target specified by FDP 
  
  
• Generating VFP tables as input for 3D simulations 
  
  

Technology

Most reservoir engineers exploit material balance thinking which is based on long-term well-by-well surface flowrate targets  (whether producers or injectors).

In practice, the flowrate targets are closely related to bottomhole pressure and associated limitations and require a specialised analysis to set up the optimal lifting (completion, pump, chocke) parameters. 

This is primary domain of WFP – Well Flow Performance analysis.

WFP – Well Flow Performance is performed on stabilised wellbore and reservoir flow and does not cover transient behaviour which is one of the primary subjects of Well Testing domain.

The conventional WFP – Well Performance Analysis is perfomed as the  $//<![CDATA[ \begin{array}{l}\{ p_{wf} \ {\rm vs} \ q \}\end{array} //]]>$ cross-plot with two model curves:

• Inflow Performance Relation (IPR) – responsible for reservoir deliverability (see below)
  
  

• Vertical Lift Performance (VFP), also called Tubing Performance Relation (TPR) – responsible for well deliverability  (see below )

The intersection of IPR and VFP curves represent the stabilized flow (see Fig. 1)

Given a tubing head pressure  $//<![CDATA[ \begin{array}{l}p_s\end{array} //]]>$ the WFP Junction Point will be dynamic in time depending on current formation pressure (see Fig. 2) and formation saturation (see Fig. 3). 

Workflow

1. Check the current production rate against the production target from FDP
   
   
2. If the diffference is big enough to justify the cost of production optimization (see point 8 below) then proceed to the step 3 below
   
   
3. Assess formation pressure based on well tests
   
   
4. Simulate IPR/VFP based on the current WOR/GOR
   
   
5. Calculate the stabilized flow bottom-hole pressure
   
   
6. Gather the current bottom-hole pressure $//<![CDATA[ \begin{array}{l}p_{wf}\end{array} //]]>$
   
   
7. Check up the calculation aganst the actual  $//<![CDATA[ \begin{array}{l}p_{wf}\end{array} //]]>$
   
   
8. Recommend the production optimisation activities to adjust bottom-hole pressure  $//<![CDATA[ \begin{array}{l}p_{wf}\end{array} //]]>$:
   
   
   • adjusting the choke at surface
     
     
   • adjusting the pump settings from surface 
     
     
   • changing the pump depth
     
     
   • changing the tubing size
     
     
   • changing the pump
     
     

The above workflow is very simplistic and assumes single-layer formation with no cross-flow complications.

In practise, the WFP – Well Flow Performance analysis is often very tentative and production technologists spend some time experimenting with well regimes on well-by-well basis. 

References

Joe Dunn Clegg, Petroleum Engineering Handbook, Vol. IV – Production Operations Engineering, SPE, 2007

Michael Golan, Curtis H. Whitson, Well Performance, Tapir Edition, 1996

William Lyons, Working Guide to Petroleum and Natural Gas production Engineering, Elsevier Inc., First Edition, 2010

Shlumberge, Well Performance Manual