The influence of fold and fracture development on
reservoir behavior of the
Lisburne Group of northern Alaska

Principal Investigator:	Dr. Wesley K. Wallace
Co-Principal Investigators:	Dr. Catherine L. Hanks Dr. Michael Whalen Dr. Jerry Jensen (Texas A&M)

Department of Energy Award DE-AC26-98BC15102

Downloadable Reports

Carbonate rocks of the Carboniferous Lisburne Group form a major hydrocarbon reservoir in the North Slope of northern Alaska. Folded and thrust-faulted rocks of the Lisburne are an important potential exploration target in the foothills of the Brooks Range and in the coastal plain of the Arctic National Wildlife Refuge (1002 area). However, relatively little is known about the reservoir characteristics and behavior of the Lisburne and how they change as a result of deformation. As in many carbonate reservoirs, most hydrocarbon production from the Lisburne is from naturally occurring fractures. A clearer understanding of these fractures could aid in future recovery from this difficult to produce reservoir.

Members of the Tectonics and Sedimentation Research Group have initiated a study of the development of fold traps in the Lisburne and how folding influences reservoir characteristics and behavior. The objectives of the study are to:

•Document the evolution of trap-scale fold geometry with increasing shortening, with emphasis on changes in thickness across the fold and with respect to mechanical stratigraphy.

•Determine patterns in fracture distribution and density within a fold trap as a function of mechanical stratigraphy and of position within folds at different stages of evolution.

•Use these observations to constrain predictive models for the evolution of trap-scale fold geometry and the resulting distribution and density of fractures.

•Use observations of natural folds and predictive fold models as a basis for fractured reservoir models for fluid flow and wellbore placement strategies in folded carbonate reservoirs.

These objectives will be met using an interdisciplinary approach involving stratigraphy and sedimentology, structural geology, and reservoir engineering. Baseline characteristics of the Lisburne reservoir will be determined using subsurface data from the Lisburne oil field and from the least deformed Lisburne exposed on the surface. These data will form the basis for models of fluid flow in undeformed Lisburne reservoir. Natural folds that represent a range of stages in fold evolution in the Lisburne will be studied in the northeastern Brooks Range to determine fold geometry and kinematics and to assess changes in fracture distribution and density during folding. The results will be used to develop predictive models for fold geometry and kinematics and for the character and distribution of porosity and permeability resulting from folding. These models will be used to develop models of the reservoir behavior within folds and to develop wellbore placement strategies in folded reservoirs.

This study will produce results that apply to current production in relatively undeformed Lisburne and to future exploration in deformed Lisburne. At least as important, the results will apply generally to folded carbonate reservoirs, which are major producers and exploration targets worldwide.

The project will be conducted over the three-year period from May 1, 1999 to April 31, 2002. Funding for the study is provided by the Department of Energy and the Geophysical Institute.

Current results

Lisburne stratigraphy and sedimentology	Detachment fold geometry
Fracture distribution and character	Reservoir characterization