Merging Satellite Images and Maps to Improve Operations, Niger Delta, Nigeria

ELLIS, JAMES M., PAT D. CALDWELL, and PETER B. GOODWIN, Chevron Overseas Petroleum Inc., San Ramon, CA

Satellite images that are merged with digital maps provide an accurate and cost-effective base for analyzing petroleum activity, environmental conditions, and culture across the Niger delta. Landsat Thematic Mapper (TM) images reveal numerous uncharted shoals and spits (approaching 2 km in length) along the margin of the delta (best displayed on TM visible bands 1 and 2). It also documents extensive changes (erosion/accretion nearing 2 km) and errors in existing maps of the delta's coastline (drawn from 1950s air photo mosaics). TM band 4 clearly delineates the land/water contact of widespread mangrove swamps. This infrared (IR) band reveals a complex network of natural and manmade channels and variations in swamp vegetation related to water depth. On upland portions of the delta, roa s, villages, urban centers, and clearings (including seismic lines) are best delineated with TM band 7 (IR). Offshore gas flares are best detected with TM visible bands 2 and 3.

Acceptable Landsat and SPOT images are usually acquired between November and February when clouds and airborne dust ("Harmattan") are at a minimum. Landsat TM imagery was selected as the optimum onshore sensor primarily because the three reflected IR bands retain their resolution during mild Harmattan conditions (visible-light images are severely degraded). Black and white SPOT imagery (10 m resolution, one band) is used to resolve offshore petroleum structures, when atmospheric conditions permit. Clear SPOT images can be merged with color TM to maximize onshore information. Existing airborne radar images (acquired 1976-1977) are excellent for regional geology, but cannot support current, large-scale (1:100,000) mapping requirements.

In order to upgrade satellite images into map-oriented, large-scale plots useful for field operations and to correct the geographical content of basemaps, images and maps were digitally merged together. Images are registered to Nigeria's "Colony Grid Belt" map projection, and map files (Lat/Long, wells, seismic, facilities, names, etc.) are digitally embedded into the images. Wells, surveyed monuments, and Global Positioning System (GPS) fixes that are visible on the images are used for this registration.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)