What’s not specifically clear in G40 is that Pressure Transient Analysis (PTA) is acceptable for estimating Initial Pressure Oil and Initial Pressure Gas conditions.
- Misconception #1: all tests have to pass the 2 kPa Rule. Not True.
- Misconception #2: if a test doesn’t pass the 2 kPa Rule it has to be shut-in >14 days. Not True.
- Misconception #3: all tests have to be shut-in >14 days. Not True.
In most cases, with a minimum eight hours (8 h) of subsurface transient pressure data, it doesn’t matter whether-or-not the test meets the 2 kPa Rule. PTA has been used for many decades to extrapolate build-up and fall-off tests to a theoretically stable point in time (p*). We can analyze DFIT & PID tests (PTA) to provide the ERCB with the extrapolated pressure (p*). The advent of digital data submissions required the programming of “business rules” for the Board’s computer to check, before accepting ERCB.pas files. Unfortunately the 2 kPa and 14 Day Business Rules have been misinterpreted. There are two critical lines in the TRG.pas file:
~TEST DATA,INTRP.,Y,Test Interpretation Present
~PRESSURE RESULTS – SUMMARY,PEXTR.KPAA,9558.00,Representative Extrap/ False Pressure
That innocuous ‘Y’ flags the business rules not to apply the 2 kPa Rule and look instead for the p* (PEXTR).
I know of engineers wasting time and money: excessive shut-in times; re-running recorders; conducting follow-up gradients; or writing waiver applications, then having to pull rods and pump anyway… All due to G40 misconceptions.
Send us some data – we’ll tell you if it will pass with PTA. Then please give us a call – we can discuss going forward with economic methods for regulatory compliance.