Janell Edman¹, Eric Jameson², Tony Perkins², Gary Guthrie²

(1) Consultant, Denver, CO
(2) Marathon Oil Company, Houston, TX

ABSTRACT: Mississippi Canyon 348: case study of a deep-water biogenic gas accumulation

Mississippi Canyon 348 (Camden Hills) is a recently discovered biogenic gas field in the deep-water (7200 ft) Gulf of Mexico. Briefly, the gas is stratigraphically and structurally trapped in a multi-story, distal turbidite channel sand complex. Although considerable work is published on biogenic gas that has been generated and trapped in shelf and deltaic depositional systems, little is understood about biogenic gas accumulations in distal, deep-water, low net sand depositional settings such as this. Consequently, from a number of perspectives, this field provides an interesting case study. First, it is likely the biogenic gas was generated by bacterial activity in deep-water turbidite sands and then concentrated by formation of gas hydrates. Once these gas hydrates reached temperatures where they became unstable, they melted, and the gas was able to migrate. Second, at some point along the migration pathway, the biogenic gas took trace amounts of thermally-generated hydrocarbons into solution, probably by some sort of gas washing process. The biogenic gas then charged virtually every sand with adequate porosity and permeability over a vertical interval of at least 4000 ft. Third, not all of these charged sands form economic reservoirs, and the individual sands tend to be vertically compartmentalized by intervening shales. However, gas in the primary reservoir is in fluid communication laterally. Given the water depth, reservoir compartmentalization, and possible water encroachment during production, field development is likely be technologically challenging.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado