Abstract

Deep Source Gas research is focused on the hypothesis that natural gas is generated in sediments carried to great depths at convergent plate boundaries in the earth's crust. These deeply emplaced plate boundaries in the earth's crust. These deeply emplaced sediments may source gas to shallower, drillable traps through deep fracture systems. Many areas of North America are believed to have experienced plate tectonic convergence. The western Cordilleran geologic province in particular appears to have thrust fault structures (associated with subduction and abduction) that enabled deep emplacement of hydrocarbon-generating sediments during more recent geologic ages (during the last 180 million years). The specific area of interest in this province encompasses approximately 1.5 million square miles of the western U.S. (including Alaska) and Canada; other portions of this same province extend southward into Mexico and Central and South America.

The ongoing research consists of basic studies of hydrocarbon generation, stability, and preservation at depths in excess of 30,000 feet in addition to a comprehensive evaluation of the geologic structures, stratigraphy, and geochemistry of the above region.

Results to date include geologic and geophysical evidence of deeply emplaced sedimentary rock units at depths exceeding 30,000 feet in western Washington and south central Alaska, a new methodology for verifying deep methane stability via fluid inclusion studies, and a preliminary gas resource estimate of 3,000 Tcf. If only a fraction of the gas thought to exist is found to be recoverable, it could have a profound influence upon the international energy industry.

Introduction

There is general agreement that natural gas will continue to be an important alternative to other energy sources. Since 1976, the U.S. Department of Energy (DOE), Morgantown Energy Technology Center (METC) has been involved in unconventional gas recovery (UGR) research to characterize this resource and to enable the exploitation of natural gas from reservoirs that would otherwise be considered economically unrecoverable. The research has focused on low porosity, low permeability, or otherwise undeveloped resources whose sources and reservoirs are at conventional depths (15,000 feet).

In 1982, a new effort emerged that was a natural outgrowth of DOE/METC's experience in UGR research. Natural gas resources are being investigated that require long-term, high-risk research and development, but offer a significant potential payoff. The level of risk is such that little or no private sector research is envisioned for the near future.

A workshop held in 1982 in Morgantown, West Virginia, addressed the subject of deep source gas from the perspective of three separate emplacement concepts: abiogenic gas, subducted organic-origin gas, and deep intracratonic sedimentary basin gas. Following the workshop, it was decided that METC research of deep source gas would focus on the subducted, organic-origin gas concept. DOE/METC will continue to monitor the abiogenic gas research supported by the Gas Research Institute (GRI).

The existence of methane or methane-generating source rocks at great depth in the earth's interior remains theoretical. If the existence of such gas was merited, it could radically influence the methods used to explore for new supplies. If even a fraction of the deep gas thought to exist proves to be recoverable, it could have a profound influence upon the international energy industry.

The nature of the deep source gas resource has yet to be identified.

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