Occurrence of Pore-Filling Halite in Carbonate Rocks, Nesson Anticline, Williston Basin, North Dakota

Edward J. Bucher

Clear, colorless pore-filling halite of late diagenetic origin occurs locally in the Devonian Dawson Bay, Winnipegosis, and Ashern Formations, the Silurian Interlake Formation, and the Ordovician Red River Formation. The halite occludes a variety of pore types and individual pores are filled with single crystals or aggregates of only a few crystals. This halite is present in quantities ranging from a trace to approximately 12%.

Cores from McGregor field, Williams County, show the Winnipegosis Formation consists of mixed-skeletal lime wackestones and mudstones. These contain vugs up to 4 in. (10 cm) in size, intraparticle pores, and shelter porosity within pelecypod shells, up to 4 in. (10 cm) in size, which are occluded with halite. Halite also fills common small discontinuous vertical fractures.

The upper 200 ft (61 m) of the Interlake Formation locally exhibits the most striking occurrences of pore-filling halite. These dolostones consist predominantly of intraclast-peloid mudstones, wackestones, packstones, occasional grainstones, algal boundstones, and solution-collapse breccias containing vug, fenestral, interparticle, shelter, intercrystalline, moldic, channel, breccia, and fracture porosity types. All porosity types, except intercrystalline, can be halite filled.

A rare occurrence of pore-filling halite exists in Red River cores from Blue Buttes field, McKenzie County, where a dolomitic, mixed-skeletal, lime mudstone and wackestone lithofacies contains vugs, discontinuous vertical fractures, and intraparticle porosity types occluded with halite.

In most occurrences, the pore systems were noneffective prior to halite infilling and had no potential as hydrocarbon reservoirs. However, it has been demonstrated that halite plugging in the Interlake Formation has locally formed updip seals to hydrocarbon migration.

AAPG Search and Discovery Article #91033©1988 AAPG Rocky Mountain Section, Bismarck, North Dakota, 21-24 August 1988