Aeromagnetic Imaging of Faults in the Piceance Basin Gas Play

with Seismic and Drilling Confirmation

By

William C. Pearson

Pearson Technologies Inc., Lakewood, CO

David A. Uhl and Steve R. Moore

EnCana Oil & Gas (USA) Inc, Denver, CO

Recent technologic advances in aeromagnetic acquisition, processing, imaging, and interpretation provide effective methods for locating faults and basement structures in sedimentary basins. In some instances a pattern of open fractures or intersecting fault trends causes good gas reservoirs. In other instances wrench faults are mineralized and act as seals to adjacent gas pressure compartments.

Studies of Landsat imagery, aeromagnetic surveying and 3-D seismic in Rulison and Mamm Creek gas fields confirm a picture of significant basement structuring. Gas production is principally from tight sands in the Williams Fork Formation of the Upper Cretaceous Mesa Verde Group. Individual wells vary from non-commercial to over 3 Bcf EUR within short distances. The more economic wells are on structural flexures defined by well tops and seismic data. However, bounding faults as defined by seismic and magnetic data produce significant reservoir heterogeneity. 3-D seismic is a most effective tool but its use is restricted in the Piceance Basin due to limited surface access and cost considerations. Aeromagnetic surveying is unencumbered by surface restrictions, is very fast to acquire, and is inexpensive compared to seismic, leasing, and drilling.

Recognizing regional structural trends and fault patterns in prospective basin-centered gas plays is a critical element based on known analog fields. Seismically interpreted faults and magnetically imaged faults in the Green River Basin of Wyoming have confirmed that sealing faults bound the recently developed, 1 TCF Jonah Gas Field. The similarity to the observed pattern of bounding faults around the better producing wells in Rulison and Mamm Creek Gas Fields point to a picture of compartmentalization of tight gas reservoirs.

AAPG Search and Discovery Article #90004©2002 AAPG Rocky Mountain Section, Laramie, Wyoming