Gas Production Sweet Spots in the Jonah Field

By

Ronald C. Surdam, Zunsheng Jiao, and Nicholas K. Boyd

Innovative Discovery Technologies, Laramie, WY

Velocity studies neatly delineate the regional distribution of anomalously pressured, gascharged rocks in the Lance Formation in the vicinity of the giant Jonah gas field. To more accurately determine the production sweet spots (i.e., areas of enhanced storage and deliverability) in the Lance Formation, a velocity function (Vf) is constructed that correlates with estimated ultimate recovery values (EUR) observed from drilled gas wells. By crossplotting EUR and Vf , it is possible to accurately predict the production performance of any site in the field that can be characterized by a seismic interval velocity/time (depth) profile. Spatial sampling of the predicted EUR is then only a function of the CDP interval (110 ft in the case of Jonah).

Integrating the velocity attributes of the Jonah field with the regional tectonic setting strongly suggests that the production sweet spots primarily are structurally controlled. The spatial distribution of the sweet spots appears to be controlled by the interaction between the strike-slip fault bounding the field to the south, the scissor fault bounding the field to the west and northwest, and internal "pull-away" faults inside the two boundary faults. The sweet spots are located where tensional fractures are optimized within the block formed by the boundary faults.

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