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An Overview of Hydraulic Fracture Mapping in the Jonah Field and Its Implications for Field Development and Completions

Jeff Johnson1, Dean Debois1, Scott Malone1, Norm Warpinski2, Chris A. Wright3, and Leen Weijers4
1EnCana Oil and Gas (USA), Inc., Denver, CO
2Pinnacle Technologies, Houston, TX
3Pinnacle Technologies, San Francisco, CA
4Pinnacle Technologies, Centennial, CO

The lenticular sands of the Lance formation in the Jonah Field in South-West Wyoming require a special completion strategy for the best economic development. The Jonah field is a large, structurally complicated wedge shaped fault trap in the Green River Basin. Production is primarily from an over-pressured stacked sequence of 20 to 50 fluvial channel sands in the Lance Formation.

The main reservoir issues in Jonah are low permeability and small pay sections across a large gross interval. Hydraulic fracturing is required to sustain commercial production in these low permeability reservoirs and wells in the Lance are stimulated in multiple fracture stages. Each fracture stage may target three to six sand bodies with eight to twelve stages per well.

With about 13 Tcf of OGIP over an area of about 23,000 acres, the operator embarked on an aggressive strategy to determine the best infill drilling and completion strategy by directly measuring fracture growth on hundreds of fracture treatments in various pilot areas in the field. Direct fracture mapping technologies such as microseismic and tilt mapping played a major part in the decision-making process to determine well placement, infill drilling, staging and fracture treatment design.

This paper provides a management level summary, will provide an overview of the Jonah Field and present details of the following general findings from fracture mapping:
- Main fracture azimuth is generally N 45° W. The well pattern was adjusted to accommodate this;
- Multi-directional complex fracture growth;
- Fracture half-lengths are 600 to 800 ft for normal fracture treatments, but effective half-length are significantly smaller;
- Fracture height growth is mainly driven by the effectiveness of shale barriers;
- Unexpected faults have been encountered and showed a significant impact on fracture growth behavior.

AAPG Search and Discovery Article #90092©2009 AAPG Rocky Mountain Section, July 9-11, 2008, Denver, Colorado