their ongoing effort to wrest the new from the old, oil finders
are discovering that more often than not it takes a mix of different
technologies to achieve success.
the technology used to find new pay in old plays and bypassed pay
in old fields is what you would expect, such as 3-D seismic. Some
of it, however, smacks of the more esoteric, such as geochemical
exploration, which focuses on the search for analytically-identifiable
surface or near-surface occurrences of hydrocarbons as clues to
the location of undiscovered oil and gas.
hydrocarbon microseepage surveys have come to be recognized as a
flexible, low risk and low cost technology that complements the
more traditional geologic and seismic methods.
in geochem technology and the results of some recent applications
will be recounted by Deet Schumacher of Geo-Microbial Technologies
(GMT), Ochelata, Okla., in a paper at the AAPG Mid-Continent Section
meeting this month in Tulsa. Schumacher also presented a geochem
paper at the recent AAPG International Conference and Exhibition
been documented that hydrocarbon microseepage from petroleum accumulations
is both widespread and vertical except in the case of very complex
geology, according to Schumacher. This microseepage is also dynamic
in that it responds quickly to changes in the reservoir.
make surface geochemical surveys suited for a whole new array of
applications beyond the more established uses for high-grading leases,
leads and prospects, including:
delineation of field limits.
by-passed oil and gas.
of infill and step-out locations.
to reservoir characterization studies.
of hydrocarbon drainage over time.
of waterflood and CO2-flood operations.
do a well-designed survey and outline an anomaly," Schumacher said,
"it can approximate the distribution of the producing reservoir
one productive zone in the area it makes it simple," he said, "but
multiple zones make it much more difficult. If there's stacked pay,
you must look at other information to see which zone seems to best
fit the anomaly."
cited the example of an old field in Argentina with multiple pay
zones, where a geochem survey was used to look for bypassed pay
and for other applications.
of nice anomalies showed up," he said, "and when you compare a map
of the anomalies with the three productive zones, only one matches.
It's a nice structural closure, and contours on the structure show
the closure matches nicely with the geochem.
we drill, we won't have proof that's the source.
the limitation of these methods," Schumacher added. "We can't tell
depth, so we usually compare maps on different horizons."
also cites the results of some recent GMT geochem surveys in western
Venezuela -- one of which, in an old, nearly depleted field, focused
on searching for areas of by-passed pay.
an area of high microseepage was identified next to a trapping fault,
representing a part of the field that hasn't been effectively drained
by existing wells. Schumacher noted there are opportunities here
for several new wells and/or recompletions.
Hydrocarbon microseepage profile and seismic section across
a recent discovery in western Venezuela.
This is an example of a surface geochemical anomaly associated
with an oil field that is just beginning to be developed.
Geochemical samples were collected at 300m intervals along
seismic lines to identify the probable limits of the productive
reservoir. The most prospective area for future drilling occurs
west (left) of the wells. Also note the low seepage values
in the immediate vicinity of the 2 producing wells, possibly
due to depressurization of the reservoir due to production.
geochem survey of a nearby field indicated a strong hydrocarbon
of the anomaly indicates the probable extent of the productive reservoir
at depth," Schumacher said. "Such information can help guide placement
of development wells and/or placement and extent of a post-discovery
profile also shows two well-defined geochem lows in the immediate
vicinity of the producing wells, which is seen commonly," he said.
"Seepage is dynamic, and within weeks to months of a new well going
on production, the magnitude of the seepage anomaly decreases dramatically
within 100 to 200 meters of the well location."
to Home ...
GMT success story that occurred closer to home is the Park Springs
Conglomerate field in Montague County, Texas, where a client initially
identified an Ellenberger high as his drilling prospect using 3-D
survey was implemented using the Microbial Oil Survey Technique
(MOST). Developed by Phillips Petroleum and modified by GMT, MOST
is based on the presence of hydrocarbon microseepage above buried
accumulations. Active microseepage is detected by measuring the
concentrations and distributions of hydrocarbon-indicating microorganisms
found in shallow soils.
course of the Montague County survey, 167 shallow soil samples were
collected in accordance with MOST procedures to evaluate the hydrocarbon
microseepage patterns of the roughly 3.5-square-mile area previously
characterized by the 3-D survey. Because this area had no producing
wells prior to this project, it represents a wildcat exploration
program, according to Schumacher.
survey revealed only a minor seep anomaly associated with the high,
which harbored the selected drilling target. However, it showed
a strong, extensive seepage anomaly over the low on the Ellenburger
drilled on the crest of the structure turned out to be non-commercial.
then re-evaluated the geology and considered other play possibilities
that might be consistent with the geochem lead," Schumacher said.
"They said there must be a good geologic reason for seepage to be
focused over the low and postulated there might be Pennsylvanian
sands and conglomerates in that area."
and made a field discovery, which has turned into a 14-well field
in an old, highly-explored area.
holes also were drilled in the conglomerate feature, but they were
located in areas outside of the microbial microseepage anomalies,
can be pointing the way, but you still have to evaluate it," he
cautioned. "It has to make geologic sense."