Abstract

Lateral Components of Vertical Migration (What Happens When Things Go Sideways)

Gary Rice
GeoFrontiers

Vertical migration is the cornerstone of near-surface geochemical exploration. Below the water table gases migrate vertically in a separate phase with upward movement due to buoyancy. The surface expression of hydrocarbon gases rising vertically from reservoirs makes possible detecting and mapping petroleum reservoirs.

Lateral migration along bedding planes occurs, but is minor compared with the vertical migration component. However, even slight lateral migration can be important when mapping narrow reservoirs. Some Permian reservoirs on the Eastern Shelf of the Midland Basin exhibit lateral migration. These case studies show how lateral migration had an impact on interpretation of petroleum reservoirs from geochemical exploration data.

Wages Dreamfield (Tannehill Ss) in King County, Texas, included five producing wells surrounded by dry holes. Geochemical interpretation integrated with subsurface geology recognized a slight eastern (up-dip) lateral migration that was successful in predicting a narrow channel between two dry holes.

Grantham field (Tannehill Ss) in Dickens County, Texas, was discovered from a dry hole and regional mapping. Geochemical data indicated significant hydrocarbons over the prospective area and was one of the primary tools used during development. However, a local southerly dip created a small offset in the surface expression of this reservoir.

Recognizing lateral migration improved the accuracy of geochemical data interpretation in these case studies. Knowledge of regional and local dip helped improve the accuracy of reservoir locations from surface expressions. This paper discusses When to look for, How to recognize, and How to understand lateral migration components that will influence geochemical exploration data and subsequent interpretation.

AAPG Search and Discovery Article #90164©2013 AAPG Southwest Section Meeting, Fredericksburg, Texas, April 6-10, 2013