What characterizes abnormal pressure in geological formations?

Abnormal pressure in geological formations is primarily characterized by pressure that exceeds formation water hydrostatic pressure. This condition develops when the pressure in the pore spaces of the rock formations becomes greater than what is normally expected based on the weight of the water column above it. Under normal conditions, the hydrostatic pressure in a formation increases with depth due to the weight of the overlying water.

When pressure exceeds this hydrostatic level, it is described as abnormal pressure or overpressure. This situation can arise from various geological processes, such as rapid sedimentation, reduced drainage due to impermeable layers, or the presence of gas in the formation. Such pressures can pose challenges during drilling, as they can lead to kicks or blowouts if not properly managed, making it crucial for operators to understand and anticipate these conditions.

Other options describe different pressure conditions or factors unrelated to the definition of abnormal pressure. For instance, stable formation fluid pressure indicates that the pressure levels are normal and conforming to expected values, which is the opposite of what characterizes abnormal pressure. Atmospheric pressure reflects the pressure exerted by the weight of the atmosphere, which is not relevant to subsurface geological conditions. Reduced drainage capability may relate to pressure build-up but does not define abnormal pressure itself; rather,