SURFACE
HYDROCARBON DETECTION SHOWS PROMISE
PTTC Home Solutions From the Field
Based on a workshop sponsored by PTTC's Eastern Gulf Region on
February 10, 1999, in Jackson, MS.
BOTTOM LINE
Operators can use surface geochemical techniques
for reservoir characterization, field development, and monitoring
production patterns, as well as more established uses for high-grading
leases, and prospects. Wider usage of surface geochemical exploration
methods in mature basins also shows great promise.
PROBLEM ADDRESSED
Hydrocarbon micro-seepage, which can be
measured by various surface geochemical techniques, is common.
Leaked hydrocarbons move predominantly in a vertical direction
(with geological exceptions). Data confirm that oil and natural
gas production levels respond quickly to changes in reservoir
conditions. There are dependable predrilling methods available
to quickly screen areas for oil and natural gas, such as surface
geochemical prospecting technologies. These can be used in conjunction
with other data to reduce exploration costs and increase success
rates. After drilling, geochemical methods can be used to define
the limits of production and identify bypassed hydrocarbons.
KEY WORDS:
Surface Hydrocarbon Detection, Geochemical,
Prospecting, Geochemical Methods, Hydrocarbon Leakage
SPEAKERS
Geochemical Technologies:
Deet Schumaker, Geo-Microbial Technologies
Science & Statistics of Geochemistry:
Joel Gervitz, InterScience
Data Integration:
Gary Rice, GeoFrontiers Corp.
Prospecting Using Geochemistry:
Paul Harrington, W. L. Gore & Associates
Canadian Hunter's Experience Using Geochemical Methods:
Richard Wyman, Wyman & Associates
TECHNOLOGY OVERVIEW
Geochemical exploration surveys can establish
the presence and distribution of hydrocarbons and relate them
to specific exploration and exploitation needs. For reconnaissance
surveys, seeps and micro-seeps are direct evidence that hydrocarbons
were generated.
The composition of the seeps can indicate whether the geological
play is most likely to contain natural gas or crude oil. The
seepage data allow explorationists to quickly and economically
screen large areas for targets of greatest interest. For example,
reconnaissance surface geochemical surveys can be used to guide
the location and extent of subsequent seismic coverage.
For evaluating exploration leads and prospects, geochemical surveys
can identify areas associated with strong hydrocarbon anomalies.
This allows operators to high-grade their prospects on the basis
of hydrocarbon indicators. For development projects, detailed
microseepage surveys can help evaluate infill or stepout drilling
locations, delineate productive limits of under-developed fields,
and identify bypassed pay or uncontacted reservoir compartments.
Geochemical survey results add value to seismic data by identifying
hydrocarbon-charged reservoir compartments.
The design and sampling of geochemical surveys are flexible-influenced
by the exploration objectives, geological setting, and target
size, among other considerations. For regional studies, data
may be collected along seismic lines or designed to traverse
across features of structural or geological significance.
Sample spacing for geochemical surveys may vary from 500 to 1,000
meters (m) at one extreme, to 50 to 100 m at the other. The use
of sampling grids is recommended for small exploration targets.
Whenever possible, operators should sample over a recent discovery
to calibrate the data. In active fields, contours of microbial
data may indicate low values adjacent to wells due to pressure
depletion related to production. Bypassed production can be seen
by isolated microbial anomalies (" highs").
LESSONS LEARNED
1. Vertical micro-seepage of hydrocarbons
(both oil and gas) is easily detected by surface geochemical
methods. However, neither the depth of the reservoir( s) nor
the amount of hydrocarbon present can be determined by geochemical
prospecting.
2. Reconnaissance geochemical surveys used in conjunction with
other data, such as 3-D seismic, provide an effective method
to detect bypassed oil and determine the productive limits of
a field.
3. Success with geochemical prospecting depends upon selecting
the right method and using proper sample design and quality control.
It also is necessary to have calibration to known oil and gas
occurrences, and integration with other available surface and
subsurface data.
4. The potential benefits of a successful geochemical exploration
program include:
* Direct detection of hydrocarbons
* Documentation of source rock, hydrocarbon maturation, and migration
* Ability to high grade areas prior to purchasing leases or conducting
seismic surveys
* Leads for further evaluation after running seismic surveys
* Geochemical data to constrain mapping of amplitude anomalies
between seismic lines
* Evaluation of areas where seismic surveys may be ineffective
* Ability to locate traps poorly imaged with seismic
FIELD RESULTS
Case histories document an excellent predictive
capability for surface geochemical techniques. One study in the
early 1980s in Kansas and Colorado used soil samples collected
at 0.1-mile intervals within 0.5 miles of 49 proposed well locations.
All geochemical analyses and interpretations were completed prior
to drilling. Thirty-nine wells were subsequently drilled (ignoring
the surface geochemical study), yielding three producing wells,
three non-commercial wells, and 33 dry holes. The microbial survey
correctly predicted all 33 dry holes, the three producing wells,
and two of the three non-commercial wells. Additional case histories
support surface geochemistry's ability to high-grade locations.
Case studies from a variety of petroleum provinces verify that
integrating geochemical detection methods with 3-D seismic data
can increase success rates, thus lowering oil and gas finding
costs. Canadian Hunter increased its drilling success rate to
71% by combining geochemical techniques and 3-D seismic. This
is more than double the drilling success rate of 34% using seismic
data alone. By integrating geochemical data with 3-D seismic
data, operators in South America achieved a 95% drilling success
rate, and reduced their finding costs by 43%.
Within producing fields, geochemical methods can be used to define
productive field limits and aid field development and management.
Although the strategy cannot predict a project's economics, it
can determine whether hydrocarbons are present in the target
area.
CONNECTIONS:
Joel Gevirtz, Interscience
1838 W. Alabama,
Houston, TX 77098
Phone 713-522-6244, Fax 713-522-2044, E-mail intsci@ix.netcom.com
Paul Harrington, W. L. Gore Assoc.
100 Chesapeake Blvd., Box 10
Elkton, MD 21922-0010
Phone 410-566-4773, Fax 410-506-4780, E-mail pharring@wlgore.com
Gary Rice, GeoFrontiers Corp.
5130 Boyd Blvd., Suite A
Rowlett, TX 75088
Phone 972-412-7959, Fax 972-412-7942
Deet Schumacher, Geo-Microbial Technologies
PO Box 132,
Ochelata, OK 74051
Phone 918-535-2281, Fax 918-535-2564, E-mail GMTgeochem@aol.com
Richard Wyman, President
Wyman & Associates
University Research Park
400 Wakara Way,
Salt Lake City, UT 84108
Phone 801-584-2475, Fax 801-584-2406
For information on PTTC's Eastern Gulf Region and its activities
contact:
Ernest A. Mancini, Professor of Geology, University of Alabama
Box 870338 202 Bevill Bldg. Tuscaloosa, AL 35487
Phone 205-348-4319, Fax 205-348-0818, E-mail emancini@wgs.geo.ua.edu
Disclaimer: No specific application of products or services
is endorsed by PTTC. Reasonable steps are taken to ensure the
reliability of sources for information that PTTC disseminates;
individuals and institutions are solely responsible for the consequences
of its use.
The not-for-profit Petroleum Technology Transfer Council is funded
primarily by the US Department of Energy's Office of Fossil Energy,
with additional funding from universities, state geological surveys,
several state governments, and industry donations.
Petroleum Technology Transfer Council, 2916 West T. C. Jester,
Suite 103, Houston, TX 77018
Toll-free 1-888-THE-PTTC; Fax 713-688-0935; E-mail hq@pttc.org;
web www.pttc.org
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PTTC Home Solutions From the Field
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Copyright © 2001 Petroleum Technology Transfer Council
http://pttc.org/solutions/1.htm
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