Title: ”It’s a New Game!” Explorationists Challenged at RMAG Basin-Center Gas Symposium
Author: Mark Caldwell
Publication: The Outcrop, December 2000, p. 1, 8
A standing-room-only crowd jammed the Marriott City Center conference room October 6 to hear talks about exploration for basin-center gas accumulations (BCGA’s). They heard that demand for natural gas in North America is expected to double in the next twenty years, for a variety of reasons. For instance, one outgrowth of the digital revolution is a dramatic increase in electricity demand, needed to power the internet community. The theme at this symposium was that most of this country’s future gas supply must be found in onshore BCGA’s.
Symposium chairman Ben Law opened with a talk on exploration strategies for BCGA’s based on the elements and processes responsible for their formation. Law defined a BCGA as “an abnormally pressured, gas-saturated accumulation in low-permeability reservoirs, lacking a downdip water contact.” Law recognized that, while great strides have been made in understanding the geologic elements and processes of basin-center gas systems, there remains considerable confusion in the exploration community regarding their attributes. This confusion has hampered exploration and exploitation efforts.
Cretaceous rocks in sedimentary basins of the Rocky Mountains are particularly fertile hunting grounds for BCGA’s. Fred Meissner referred to the Rocky Mountain region as “the Persian Gulf of gas for the world”. The Greater Green River, Piceance, San Juan, Powder River, DJ, Uinta, and Wind River basins all contain BCGA’s in Cretaceous rocks. The mother of all BCGA’s are the San Juan Basin fields and Elmworth Field in the deep Alberta Basin, with cumulative production of many TCF of gas.
Meissner believes that geologists must challenge conventional wisdom when exploring for “areas of ubiquitous saturation”. Most of this gas will be in subcommercial, low permeability reservoirs. The exploration objective will be to locate “sweet spots” formed by stratigraphic enhancement or pervasive fracture development. Meissner focused his talk on the Green River and San Juan basin Mesaverde petroleum systems, which he likens to “gas machines”. In the eastern Green River Basin, pressure gradients of 0.45 to 0.8 psi/ft approach the “frac” gradient. The driving mechanism behind such high overpressure is that the deep basin is “currently generating hydrocarbons from contained coals within the Mesaverde”, according to Meissner.
Lee Krystinik presented a case history of exploration for an ultra-tight Frontier BCGA located on the north flank of Table Rock Field, Green River Basin. As part of an integrated exploration consortium utilizing state-of-the-art tools and intelligence, Krystinik witnessed the remarkable discovery of 14 MMCFD from a horizontal well drilled to the Frontier. This well set records for depth, horizontal coring, and flow rates despite a “scum-suckingly tight” [sic] Frontier reservoir. Buoyed by the initial success, three additional wells were drilled, but proved completely disappointing. Their sub-commercial flow rates illustrate the difficulty of exploiting BCGA’s.
John Masters delivered an inspiring keynote luncheon address entitled “New Game”. He claims that explorationists “face a revolution dictated by a doubling of gas demand. The old buoyancy traps are all used up. Established exploration methods and tools are entirely inadequate.” According to Masters, the future North American gas supply lies in onshore capillary traps or BCGA’s. Masters challenged the audience: “You have the option to change the focus of your exploration or become dinosaurs … The largest, most prolific opportunity in onshore U.S. is evaluating other company’s mistakes. The information is free in log libraries and sample warehouses.” Masters noted that Elmworth had at least 85 bypassed wells and Wattenberg 27 prior to their recognition as BCGA’s.
Numerous other speakers covered topics of local and regional interest to Rockies explorationists (abstracts volumes are available through the RMAG office). Yet all seemed to agree that exploration for BCGA’s requires approaches that are markedly different from those useful in exploring for buoyancy traps. BCGA’s do not seem to fit a model as simple as the anticlinal theory. Basin-center research has not reached a consensus on just what the new rules are. For example, water production seems to be common from BCGA’s, which superficially seems in contradiction to the idea that these are “continuous gas-saturated accumulations”.
This gathering of explorationists marked an exciting time for onshore North American gas plays. New recognition of the enormous potential for gas exploration in the Rockies, coupled with historically high gas prices, brought an air of optimism and confidence to the attendees. Talk in the aisles and over coffee rang of deals being struck, pipelines to be built, wells to be drilled, and (not incidentally) jobs for geologists. The future for natural gas appears bright. Coalbed methane, shale gas, tight sands, and conventional gas plays will all help supply our nation’s gas resources. But the messages of this symposium were that much of the long-term supply is likely to come from basin-center gas accumulations, and that geologists have an enormous challenge to understand, discover, and exploit this resource.
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