Welltest 102: Production Test Reporting
Gas (#LNG) #welltest metering requires measurement of several parameters to solve the equation-of-state: temperature, static pressure, and differential pressure. Gas gravity (density), composition (H2S, CO2, N2) and properties (pPc, pTc) should also be known.
Critical flow provers are simple gas flow meters using orifice plate theory. Gas is blown to atmosphere, so the differential pressure is assumed.
The most common type of gas flow meter is in-line, with differential pressure controlled by the backpressure valve. Orifice plate theory is employed for velocity and rate calculations.
V-Cones are simply the opposition of an orifice (hole) whereby an obstruction is placed in the flow stream. Parameters are the same as for orifice meters.
Vortex meters are being used more often for #welltesting. These place a bar in the flow path, creating flow eddies or vortices. Frequency is an input parameter. Vortex meters shouldn’t be used for frac’ sand flow back.
Hydrogen sulfide (H2S) content may require gas incineration. Propane is used as a volatile gas additive. Be sure to use correct physical properties for flow volume calculations. The relative density of propane (C3H6) is 1.45 vs. the engineering software default of 0.65. Using a relative density = 0.65 for propane metering would overestimate incineration injection rates by 50%!
