Engineering Tip: Limit Your Gradient Surveys To 4 or 5 Stops
Static pressure gradient surveys are a great way to understand your hydrostatic pressure. The idea here is to run in the hole with downhole gauges and record the pressure at various depths. This information can give you some key information about your bottomhole pressure, fluid level, and fluid density/pressure gradient. This information is extremely useful when optimizing production from a well.
The mistake many people make is that they run a lot of unnecessary gradient stops. You can calculate everything you need from four survey points, two in fluid and two in gas. A lot of people run gradient surveys with 7, 8 or 9 survey points. This is a bit of a waste of time as there is no additional information gained by all of those extra survey points. The only thing you gain from all of those extra survey points is a larger invoice!
Ideally, I like to run a gradient survey with 4 or 5 five-minute stops. It looks like this:
Point 1: TD minus 1 foot (fluid)
Point 2: TD minus 25 feet (fluid)
Point 3 (optional): TD minus 50 feet (fluid) - gives you one extra fluid point just for consistency, but not necessary
Point 4: Half way between surface and TD (gas)
Point 5: Surface (gas)
The survey points above will allow us to calculate both a fluid gradient and a gas gradient, which tells us everything we need to know. Running 7, 8 or 9 survey points does not add anything to the final calculation, it just adds time and money.