Victor H. Vega1, William B. Hanson2, Greg Partyka3, Christopher J. Christensen1, Dennis L. Cox1
(1) BP, Houston, TX
(2) BP, Hoston, TX
(3) BP, Sunbury Upon Thames, United Kingdom
Jonah Field, Sublette County, Wyoming is expected to produce at least 1.5 TCF of natural gas from lenticular, over-pressured, tight formation gas fluvial sandstones of the Cretaceous-age Lance Formation. Depth of production is 7,500 to 12,400 feet and gross producing interval is 1500 feet to 3200 feet. Jonah was indicated to be a significant field in early 1993 (Robinson, 2000) and now produces more than 350 MMCFD from more than 170 wells. In-fill drilling on 40-acre spacing has been underway since mid-2000. Entrapment may result from a combination of dip reversal and fault zone deformation associated with faults which intersect up dip to form a wedge-shaped compartment. Apparent throw on the bounding faults is variable, but commonly is less than 200 feet.
Seismic imaging of Jonah Field is challenging because of complex fault throws, and generally dim and discontinuous reflections within the producing interval. Advanced seismic techniques have been used to define the trap boundaries and to optimally locate development wells. Nearby, on the southern part of the Pinedale anticline this technology allows us to visualize Fort Union sandstone bodies comprised of coalesced meander belt channels. These sandstone bodies abruptly terminate along the west flank of the anticline suggesting a Paleocene phase of structural development. One of the main tools used for our interpretation has been a 3-D broad-band amplitude-based coherency algorithm (Marfurt, and Kirlin, 2000) that has edge detection capabilities. This algorithm looks at the reflector amplitude gradient and captures the lateral change in amplitude with azimuthal angle. This allows the interpreter to "illuminate" a particular feature from the optimal angle to see the maximum detail within the data.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado