Deliverability (Performance Type)

Use this option to define Gas Rate as a function of Bottom Hole Pressure or Wellhead Pressure. The well's deliverability is calculated from the following representation of the Semi-Steady-State equation:

Q = C(P2RES-P2BHP)n

where Q is the production rate, C is the Flow Coefficient (entered in Mscfd/psi2 or in Mm3d/kpa2), n is the Flow Exponent, PRES is the reservoir Initial Pressure defined in the Pressure Info Tab and PBHP is the flowing Bottom Hole Pressure.

Pressure Control: Choose whether the Wellhead or the Bottom Hole minimum pressure is known.

  • Bottom Hole Pressure: Enter a minimum Bottom Hole Pressure.
  • Wellhead Pressure: Enter a minimum Wellhead Pressure. In this case, the Bottom Hole Pressure is calculated from the Cullender-Smith technique (). Additional information on True Vertical Depth and Tubing Diameter can be found in the Well Geometry Tab.

Rate Control: Use this option to specify a maximum rate restriction either as a Fixed value of Max Gas Rate or as a percentage of Allowable Open Flow (% of AOF). The AOF is the flow rate at the minimum Bottom Hole Pressure or Wellhead Pressure.

When % of AOF is selected as rate control method, the decline has an imposed dynamic limit for every pressure value, calculated thus:

Max Ratep = %AOF / 100 * AOFp
where p stands for the current reservoir pressure.

AOFp = (p2)Flow Exponent * Flow Coefficient

This is equivalent to calculating the rate of the well in ideal conditions where Bottom Hole Pressure = 0.

When calculating the rate for given cum and pressure, the result is truncated by Max Ratep if needed.

Note that the equation used to calculate the friction factor of a gas flow is valid only for a turbulent flow (characterized by a Reynolds number higher than 2,1); cfr. Brett and Millheim 1986Closed Brett, J.F. and K.K. Millheim, “The Drilling Performance Curve: A Yardstick for Judging Drilling Performance”, SPE 15362. p. 334 eq. 4.46.

The rest of the inputs allow you to characterize the declines for the secondary fluids - water and gas in the case of oil producers, water and oil for gas producers.

  • Water Yield Factor: Use this option to enable input of Water Cut as a factor of rate.
  • Oil Yield Factor: Use this option to enable input of dimensionless GOR, a factor which will be multiplied by the Initial GOR defined in the Fluids Tab.
Unlike other performance types, when using Deliverability or Quadratic Pressure you cannot define either Water Yield Factor or Oil Yield Factor by means of a Table table, but only as none, as a constant or using a function.

For further details, see More on Deliverability and Quadratic Pressure.