ERCB–D40, section 4.5.7, states that “…the minimum number of pressure surveys should equal about 25 % of a pool’s producing well count, based on quarter section spacing for oil pools. This translates to one survey per productive section. For gas pools, one survey per four productive sections is required.
The reference to “one survey per X productive sections” can be confusing, especially in large gas pools which have not been fully drilled up. In these low density, or low well count pools, surveying 25 % of the drilled wells may actually leave some productive sections un-surveyed.
Shut-in, suspended, and observation wells are all first choices for annual pressure surveys. Pressure fall-off tests, on water or gas injection wells, avoids shutting in a producing well (i.e. maintaining revenue streams). Surface pressure tests are ok for annual surveys — the caveat for a gas well being that you cannot have a liquid level above the top perforation.
You have all year, so it’s a good idea to plan ahead to coincide with a scheduled plant turn-around, routine maintenance program, or pump change. If you are coordinating a field survey with a plant turn-around get all your pressure recorders installed a day-or-two before, then put the wells back on production, ready for the field-wide shut-down.
Pressure build-up and fall-off tests can be the most economic method for annual surveys as it reduces shut-in time. Again, we can use pressure transient analysis (PTA) to provide the Board with an extrapolated pressure (p*) – the test does not have to pass the 2 kPa rule or be shut-in >14 days. Just remember that we need to start the test from a producing state, to capture the flowing pressure, before we shut-in.