Page 16 - Well Control for Completions and Interventions

Introduction and Well Control Fundamentals 11

Figure 1.5 Swiss cheese—high porosity but poor permeability!

permeability, measured in micro (10 26 ), even nano (10 29 ) Darcy. They
will only flow at commercially viable rates after massive hydraulic fractur-
ing operations. Table 1.3 shows porosity and permeability from a sample
from the North Sea fields.
Understanding porosity and permeability in the reservoir is essential
for managing well control. Losses and kicks are far more likely when
working on wells with highly permeable or fractured formations.
Conversely, tight formations can create problems if a bullhead is needed
to stimulate or kill the well. Porosity data is used to estimate depth of
invasion where losses have occurred, and volume required for matrix
stimulation treatments. Knowing the size distribution of the pore spaces is
also useful for sizing solid lost circulation material, such as calcium
carbonate or sized salt.

1.1.4 Formation pressure and reservoir pressure
Hydrocarbon accumulation displaces formation water from the permeable
reservoir rock. Unless subsequent tectonic movements completely seal the
reservoir, any underlying water (the aquifer) is contiguous. Pressure in the
aquifer will be equivalent to native or regional hydrostatic gradient. In
the water column, the pressure at any depth is approximated by:
(1.1)
P 5 hG w