What Does Cross Flow Mean?
Cross flow in an oil well happens when two production zones with different pressure characteristics are allowed to communicate during production. Reservoir fluid flows from the zone at high pressure to the zone at low pressure resulting in pressure equalization. Fluids flow in some layers from the wellbore to the reservoir and in others from the formation to the wellbore.
This is commonly observed in reservoirs with high stratification where the communication between the different layers is mainly through wellbores.
Trenchlesspedia Explains Cross Flow
Crossflow is of two types namely, natural crossflow and forced crossflow. Natural crossflow occurs when hydrostatic pressure equilibrium under no-flow condition exists between all the layers. The driving mechanism for natural cross flow is the difference of diffusivity between the layers. Forced crossflow occurs when due to production activities, the injected layers are not at hydrostatic pressure equilibrium.
The driving mechanism for forced crossflow is the pressure difference between the layers. Pressure draw-down due to crossflow can lead to sand production in the wellbore which may be carried into the zones with lower pressure along with the flow of fluid.
This can lead to sand accumulation in the well also known as perforation plugging or damage to downhole equipment.