Gravity factor corrects horizontal well PI calculation

This paper reports that when a reservoir fluid's viscous force is not significantly greater than the gravity force, a gravity correction factor must be included in the productivity index (PI or J) calculations for horizontal wells located vertically away from the middle of the pay zone. For both steady state and pseudosteady-state production stages, in simulations, the PI of horizontal wells increases as the horizontal lateral's distance from the top of the pay zone becomes greater. Several methods can quickly estimate a horizontal well's productivity under different production stages including steady state and pseudosteady state.