lift is a common practice in old Gulf Coast fields. For many of
these fields, the availability -- or lack thereof -- of field gas
to run compressors, pump engines, etc., is all that stands between
production and shut-in.
of longtime operators who are picking over old fields are finding
not only little stringer gas sands to meet field needs but substantial
pay zones as well, using what appears to be a rather simplistic,
relatively inexpensive well log that's been around for more than
cased hole log comprising three tools -- gamma ray, density and
neutron curves (GDN) -- and it's found a lot of hydrocarbons for
a lot of folks since it was initially developed in 1970, according
to veteran exploration geologist Alan Pennington.
it's been dubbed the "gas-finding log" by a number of users.
frequently referred to as the "Cecil Eicke log," in deference to
the now-retired founder and owner of United Surveys (US) in Richmond,
Texas, who developed the log with help from an electronics engineer
at US, who continues as an on-site expert today.
run it for everybody, both big and small," said Eicke, who spent
his entire career in the wireline business. "There was a lot of
trial and error in developing it, and we've done a lot of fine tuning
over the years."
log appears deceptively simple: the sand shows up on the gamma ray,
and gas presence is indicated by a reversal and ultimate crossover
of the neutron and density curves. An old open hole log for comparison
and verification helps but is not essential, according to Eicke.
old log without the density-neutron curves showed interesting places,
the GDN lets the owner go in for relatively little expense to verify
gas, Pennington noted.
have used the US log for a variety of applications over the years
gas behind pipe to aid in recompletion evaluation.
abandoned wells for possible re-entry.
define depleted zones and moved water contacts in producing zones.
oil zones in some instances.
good a tool as any in the industry, cased-hole-log-wise, to indicate
reserves remaining in the well," said Richard Lee, managing member
of Masters Petroleum. "It also shows a gamma ray reversal where
a zone has been swept, so you know to stay away.
used it on close to two dozen wells up and down the Texas Gulf Coast
with incredible accuracy," Lee said.
company like Masters that makes its living re-exploring mature oil
and gas fields," Lee said, "a log like this is invaluable."
a number of more sophisticated, expensive cased hole evaluation
logs available, such as the pulsed neutron, or thermal neutron decay
(TDT) logs. For those companies who need the information a TDT provides,
such as porosity and water saturation, it's likely worth the expense.
a petrophysicist with a major may be inclined to take this path
and bypass the GDN because it is qualitative and not quantitative.
doesn't tell you porosity, but it does tell you there is gas effect,"
Pennington said. "It was developed for a niche market that doesn't
need TDT or pulsed neutron and can get along fine with a less expensive
difference in a Mercedes and a Ford Taurus," he said. "Both get
you there; it just won't be quite as in style."
number of other operators who have used the GDN, Lee noted it's
a head-scratcher as to just how the log works. Pennington says,
simply, "nobody runs a cased hole density log like they do."
known and valued primarily as a gas finder, the GDN is also a pretty
nifty tool to find oil.
run this log on 30 or 40 old wells the last couple of years," said
Richard O'Donnell, president Houston Petroleum Company, "and we've
found a lot of both oil and gas with it.
it doesn't necessarily give a crossover," O'Donnell said, "but you
can see where the density pulls in and the neutron pulls out. When
they get close, or begin to kiss, it indicates you've got some hydrocarbons
ran the log in a well at Red Fish Reef, where we saw a possible
oil zone overlooked by Exxon," he said. "We perfed, and it came
in flowing 200 bopd at 1,350 psi and no water.
experimented with a lot of different logs," Lee said, "and I find
it amazing that with all the very expensive, sophisticated tools
out there, it's the old tried and true proven technology that's
so often the best."
offers a personal endorsement for the myriad oil finders picking
over innumerable old fields today:
run this log in every well before you plug it," he said. "If you
can find a little gas sand that will make a few hundred million,
that's a lot of money -- and this thing really has made a lot of
money for a lot of people."