Geophysical Technologies Improve Success in Development of Jonah Field, Sublette County, Wyoming
House, Nancy J. 1 (1) EnCana Oil & Gas (USA), Inc, Denver, CO
3D seismic data acquired in 1996 and 1997 over Jonah field significantly improved the success ratio for subsequent drilling in the field. For the first three years the cumulative success ratio for the wells in Jonah hovered around 70%; after the acquisition and interpretation of the 3D seismic data the success ratio is above 95%.
Application of geophysical technologies has significantly impacted the development of Jonah which, due to the complex geology and physical properties of the reservoir creates special challenges. Not only mapping the structure but also to extract stratigraphy and rock properties from the seismic data requires unleashing the full arsenal of geophysical weapons available to the interpreter. The stacked fluvial channels of the Lance formation in Jonah provide no continuous mapping horizons for the interpreter upon which to base his or her analysis, and the sonic logs from wells drilled with conventional waterbased mud systems produce erroneous synthetic responses thereby further challenging the interpreter to accurately tie well results to the seismic response. Collection of VSP’s (zero-offset, offset and 3D) in various parts of the field has served to accurately tie the lithology in the well bore to the seismic response improving resolution as well as velocity calibration required by other techniques.
Determination of frac length and orientation is critical to planning optimum infill orientation and spacing. Geophysical tools for understanding resultant fracture geometry and design parameters range from borehole microseismic mapping to interpreting regional stress patterns and acquiring and interpreting dipole sonic logs.
AAPG Search and Discovery Article #90055©2006 AAPG Rocky Mountain Section Meeting, Billings, Montana