The Effect of
Hydrodynamics on Capillary Seal Capacity
Manzocchi, T.1, B.
Palananthakumar1, C. Childs1 (1)
Water drive is an efficient mechanism in
oil production. However, it has been suggested that hydrodynamic effects can be
effectively ignored in the evaluation of seal capacity over geological
timescales. It is argued that, for the relatively low water flow rates which
occur naturally, the relative permeabilities to water of trapped oil columns
are low enough that viscous forces are negligible and only the capillary
properties of seals need to be considered. This conclusion has largely been
reached by consideration of thick top seals. When considering thin seals, e.g.
fault seals, it is not clear whether pressure compartmentalisation in the
water-phase can be ignored when evaluating trapped column heights.
To examine the effect of across-fault
pressure differences on trapped column heights we have solved the two-phase
flow equations in 1D for a dipping carrier. We assume an oil column is trapped
on the down-dip side of the fault and allow water flow to be either up or down
dip. For a constant water flow rate we solve for the stable trapped column
height which provides a dynamic balance between viscous, gravity and capillary
forces. Results show that for realistic fault seals, naturally occurring across
fault pressure differences can be significant and can impact the column height
both positively and negatively depending on the water flow direction. Our
modelling also indicates that realistic hydrodynamic flow rates can also
influence the column heights supported by relatively thin or high permeability
top seals as well as fault seals.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California