Geology Reference
In-Depth Information
3.6.3
Fluid-Flow Barriers
Fluid movement, or the lack of it, through porous and permeable units can indicate the
connectivity or the lack of connectivity between wells. A
show
is a trace of hydrocar-
bons in a well, and can indicate the presence of a nearby hydrocarbon trap that is
otherwise unseen. Different water levels, oil-water contacts, or fluid pressures in nearby
wells can indicate a barrier between the wells. The structure contour map in Fig. 3.24a
and the corresponding cross section in Fig. 3.25a show four wells that appear to define
a region of uniform dip. Suppose, however, that an oil or gas show is present in the
downdip well but not in the updip wells. The show suggests proximity to a hydrocar-
bon trap, yet the map does not indicate a trap. The map must be revised to include
some form of barrier because of this additional information (Sebring 1958). Possible
alternatives that could produce an oil or gas show in the downdip well include a hydro-
Fig. 3.24.
Alternative maps honoring the
same data points.
a
Map based
on the four wells being dry
holes.
b-f
Maps based on pres-
ence of an oil show in the well
labeled
s
, implying presence of
a barrier between this well and
the three updip dry holes. Hy-
drocarbon accumulations are
shaded
. Figure 3.25 shows the
corresponding cross sections.
(After Sebring 1958)
Fig. 3.25.
Alternative cross sections in
the dip direction honoring the
same data points.
a
Section
based on the four wells being
dry holes.
b-f
Sections based
on presence of an oil show (
s
)
in the downdip well, implying
a barrier between this well and
the updip wells. Hydrocarbon
accumulations are
shaded
.
Figure 3.24 shows the corre-
sponding structure contour
maps. (After Sebring 1958)
