3.4. Deep Source Gas Project (1982-1992)
Deep source gas research was an outgrowth of DOE’s Unconventional Gas Resource
(UGR) program begun in 1976.
The fundamental concept behind the research was that
proving the existence of methane or methane-generating source rocks at great depths
(>30,000 feet) could radically influence methods used to explore for new gas supplies.
The initial impetus came from a workshop held at METC in May 1982 to discuss the
potential benefits of a research program that would investigate three possible types of
deep source gas:
- Abiogenic Gas – derived from primordial, non-biologic origin hydrocarbons in the
earth’s mantle,
- Subducted Organic Source Gas – arising from plate tectonic emplacement at great
depth of hydrocarbons from organically-derived (near surface) sources, and
- Deep Sedimentary Basin Gas – conventionally-sourced gas found in sedimentary
rocks that have been tectonically downwarped to depths in excess of 30,000 feet.
The participants in this workshop (government, industry and academia) determined there
was a need for conclusive data on the occurrence of methane from suspected deep
sources and a DOE-led program to collect and analyze such data should be undertaken.
Their recommendations included:
- Improving geophysical techniques,
- Coordinating geophysical and geochemical data to aid in evaluation of deep structural
frameworks,
- Developing an improved scheme for the differentiation of gas origins,
- Implementing a cooperative effort in acquiring deep core samples from public and
private sources,
- Expanding efforts to thermodynamically model rock gas systems, with comparisons
to deep core sample phenomena as they become available (e.g., fluid inclusions), and
- Implementing field geologic studies on the western Cordilleran region of North
America, with its relatively large unexplored area, abundant deep fault systems,
allochthonous terranes, and adjacent convergent margin.
As a result of the workshop and other discussions, subsequent METC research became
focused primarily on one of the deep source gas concepts: the subducted organic-origin
concept.
Central to this idea was the notion that natural gas could be generated in
sediments carried to great depths by plate tectonic activity along convergent margins, and
that this emplaced deep gas could also source shallower traps through deep fracture
systems (see Figure 3.4.1).
Figure 3.4.1: Schematic Illustrating the Concept of Deep Source Gas Associated with a Subduction
Zone. (Click to enlarge)
The Cordilleran geologic province of North America was considered a prime candidate
for study because it has both active and inactive subduction zones and contains thrust
fault structures that enabled deep emplacement of hydrocarbon-generating sediments
during the recent past (180 million years).
The specific area of interest in this province
encompassed about 1.5 million square miles of Western U.S., Alaska and Canada.
Preliminary geochemical studies indicated that the deep-source-gas generating capacity
of this region could be as much as 3000 Tcf.
DOE funding was focused on establishing the existence of natural gas arising from these
deep source zones, locating migratory paths, determining the existence of potential gas
reservoirs, defining target areas and quantifying resources estimates. Geological
characterization, consisting of geophysical and geochemical field studies of target areas
in Northern California, Oregon and Washington, was initiated in FY 1984.
This research
was carried out through work conducted in-house as well as in cooperation with the U.S.
Geological Survey. Additional work on theoretical studies of potential deep gas
compositional variation and the development of gas detection/differentiation systems was
also pursued.
The DOE project manager at METC primarily responsible for research efforts related to
deep source gas was William Gwilliam. The most important products that resulted from
the Deep Source Gas program were the result of the dozen or so key projects listed
below. A number of these projects were carried out under a USGS/DOE Interagency
Agreement.
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