8.2.2 Process Challenges

Standing (1981) declared “the greatest use of PVT data lies in calculating reserves of oil and gas in place in the reservoir and the effect of field operational methods on the recovery of oil and gas.” In other words, PVT data is fundamental to our ability to understand and predict resource size and recovery.

Some of the challenges (per Standing):

• No assurance that samples obtained in one well are representative of the entire reservoir.

• Gravity effects can create sample differences

• Samples at the same structural elevation may have differences based on geologic activity over time

• How representative are samples captured in a well?

• Fluid may be commingled (from multiple reservoir zones)
• Fluid may be contaminated

• Where two phases exist in contact in the same zone, flow rates are almost always different

• How complete is the samples collection data?

• Collection points, times, etc.

• How depleted is the reservoir?

• Prefer above 80% of original pressure
• Below 40% will likely lead to inaccuracies

• Samples should be re-run as reservoir depletes

References

Standing, M.B. 1981. Volumetric and Phase Behavior of Oil Field Hydrocarbon Systems, ninth edition. Richardson, Texas: Society of Petroleum Engineers of AIME.