What Does Gravitational Pressure Drop Mean?
Gravitational pressure drop is one of the three types of pressure drops experienced by a wellbore. The other two are frictional pressure drop and acceleration pressure drop. For horizontal flow, the gravitational pressure is negligible; for upward flow, the gravitation pressure drop is negative and for downward flow it is positive. Gravity is one of the important forces in the recovery of oil from horizontal wells, especially for heavy oils where the reservoir pressure is not high enough to move the oil toward the wellbore.
Trenchlesspedia Explains Gravitational Pressure Drop
One of the widely used methods to improve oil recovery is gas injection. As the injection rate of gas increases, the producing oil well experiences a decrease in gravitational pressure drop while experiencing an increase in frictional pressure drop. Horizontal wells expose a large area of the formation to the well compared to vertical wells, and are therefore used extensively in recovering oil from reservoirs.
A horizontal well placed close to the bottom of the reservoir is ideal for gravitational forces to act. However, determining gravitational and acceleration pressure drop requires a value for void fraction, which is the fraction of the channel volume occupied by the gas phase. Pressure drop (gravitational, frictional and acceleration) is a very important factor in fluid flow and should be kept at a minimum, as it increases operational cost.