In the mid-1990s,
Arco International reviewed a farm-out proposal from Enterprise
Oil for drilling on a block held by Enterprise
in the Romanian Black Sea. Enterprise already had completed a seismic
program and had mapped a variety of structures on the block.
Sediments on the block were
Tertiary sands and shales, and a review of scanty records of past
drilling suggested that hydrocarbon charge may be a concern in the
Arco's review of the seismic
data noted some subtle amplitude anomalies in off-structural settings.
Careful analysis of the data convinced Tom Velleca, Arco VP of exploration,
that the amplitude anomalies probably were indicating the presence
of hydrocarbons in thick, high porosity sands, at relatively shallow
Detailed integration of
the regional petrophysical data to the seismic data indicated that
hydrocarbons should be present in good reservoirs, but light oil
could not be differentiated from gas in the reservoir sands with
the control available.
Velleca's group accepted
the farm-out proposal from Enterprise - with the caveat that Arco
would select the drilling locations for the obligation wells.
Seeing Is Believing
Arco selected the first
location as a test of one of the amplitude anomalies. Great confidence
and a high certainty of success was expressed by the exploration
The drilling rig was located
over the seismic anomaly and drilling began.
At the anomaly level, no
sand and no hydrocarbons were seen by the shocked exploration team.
A careful repeat of the logging run showed, again, no sand and no
hydrocarbons at the seismic anomaly level.
The first reaction of the
staff was to say "Sorry, Marlan, something must have gone wrong.
We'll release the rig, (it's on stand-by and costing us money),
and we'll move on."
Instead, Velleca held the
rig and directed that the staff take a last look at the comparison
of the seismic traces to the synthetic created from the new well
There was a mismatch, at
the objective level, between the two sets of acoustical data. Velleca
pointed out that seismic doesn't lie; that well logs don't lie;
that an explanation has to be found that honors both sets of real
Velleca suggested that the
staff review the character of the near traces versus the far traces
- and an analysis by project manager Mike Richter and project geophysicist
Mark Ward noted some distinct differences in character when near
traces were compared to far traces.
"Perhaps we drilled a shale
plug in the middle of the alluvial sandstone?" suggested Tom O'
"Move the rig 300 feet and
re-drill the well!" Velleca directed. "I believe my seismic data."
Three days of drilling brought
the drill bit back to the objective horizon, and the relocated wildcat
found a thick, porous, gas-bearing sand - precisely where it had
been predicted by the seismic data.
It's one thing to see data;
it's another to believe data.
And what did I think I learned
from this discovery?
I think I learned that confidence in technology is often as important
as knowledge of technology.
I think I was reminded that one person can make the difference between
a success and a terrible failure.
least, that's the way I remember it.