Liquid loading

Brief

Liquid loading is a phenomenon when the gas phase does't provide sufficient transport energy to lift the liquids out of the well.

In 1969 Turner et al. published an empirical correlation defining the Liquid loading gas velocity.

Math & Physics

The minimum gas velocity to remove the liquid equation:

$v_g = 1.593\ \sigma^{1/4}\ \frac{({\rho_L-\rho_g})^{1/4}}{\rho_g^{1/2}}$

The minimum gas rate to remove the liquid equation:

$q_g = 3.06\ \frac{P\ v_g\ A}{T\ z}$

Discussion

To avoid the Liquid loading the gas rate needs to be maximized.

To maximize the gas rate the wellhead flowing pressure needs to be minimized.

Bigger tubing ID will increase the gas rate as well.

In case when gas rate is limited by the Reservoirs deliverability smaller tubing ID will increase the gas velocity.

Nomenclature

$A$ = flow area, ft^2

$P$ = flowing wellhead pressure, psia

$q_g$ = gas rate, MMscf/d

$\rho_g$ = gas density, lbm/ft3

$\rho_L$ = liquid density, lbm/ft3

$\sigma$ = surface tension, dyne/cm

$T$ = flowing temperature, °R

$v_g$ = gas velocity, ft/sec

$z$ = gas compressibility factor at flowing P & T, dimensionless

References

Turner, R. G., Hubbard, M. G., and Dukler, A. E. (1969) “Analysis and Prediction of Minimum Flow Rate for the Continuous Removal of Liquids from Gas Wells,” Journal of Petroleum Technology, Nov. 1969. pp. 1475–1482.