New exploration approach: Pennsylvanian Lower Tyler central Montana

Conference · Fri Aug 01 04:00:00 EDT 1986 · Am. Assoc. Pet. Geol., Bull.; (United States)

OSTI ID:7041958

Shepard, W

Modern exploration methods utilizing a plate tectonics structural model and a recent alluvial valley analog, the Brazos from the Texas Gulf Coast, have helped revive interest in Pennsylvanian Lower Tyler exploration in the central Montana petroleum province. The central Montana trough is now visualized as an aulacogen, reaching from the Rocky Mountain trench near Butte, Montana, eastward to the Williston basin. It is 60 mi wide by about 400 mi long. Pennsylvanian Lower Tyler sediments occur in this narrow east-west-trending rift system. The regional setting is an aulacogen, or intracratonic rift, that connected the Williston basin to the Cordilleran geosyncline during much of geologic time, beginning in late Precambrian. The Lower Tyler is a westward-draining Pennsylvanian (Morrowan) alluvial valley-fill system consisting of a number of river valleys that funneled into the topographic low of the aulacogen. Rift-controlled, estuarine, euxinic limestones and shales above and below the Lower Tyler provide petroleum-rich source rocks. These source rocks are mature and have generated oil, probably in the Paleocene and early Eocene. The modern Brazos River Valley of southeastern Texas is a near mirror-image analog for Lower Tyler alluvial valley fill. The Brazos valleys are 6 mi wide, 150 to 300 ft thick, and contain 60 to 70% backswamp shales and silts. Point-bar sands constitute a relatively small portion of the valley fill; the sands are 60 to 70 ft thick and about 3000 ft wide. Diagenesis has decreased net porosity distribution in the Lower Tyler to less than that of the Brazos, yet porosity parameters may still be applied to exploration in the Tyler sandstones.

• Research Organization: Infinity Oil Co., Billings, MT
• OSTI ID: 7041958
• Report Number(s): CONF-8609129-
• Conference Information: Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Journal Volume: 70:8
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
EXPLORATION
FEDERAL REGION VIII
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
MINERAL RESOURCES
MONTANA
NORTH AMERICA
PALEOZOIC ERA
PENNSYLVANIAN PERIOD
PETROLEUM DEPOSITS
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
SHALES
SILTSTONES
USA