Unraveling the timing of fluid migration and trap formation in the Brooks Range foothills:

a key to discovering hydrocarbons.

UAFC. L. Hanks, B. Coakley, W. K. Wallace

A. Duncan, A. Kleck & A. Strauch (M.S. students)

Industry:Anadarko, Encana, PetroCanada

AtoZinc, Petro-Fluid Solutions

Goals of project•Constrain the conditions & timing of the development of hydrocarbon migration pathways & reservoir enhancement (fractures) in the foothills of the Brooks Range.

•Collect real data sets to constrain broader theoretical and regional models.

Goals of project•Constrain the conditions & timing of the development of hydrocarbon migration pathways & reservoir enhancement (fractures) in the foothills of the Brooks Range.

•Collect real data sets to constrain broader theoretical and regional models.

Methods•Collect surface data that focuses on the relationship of fractures to structure and stratigraphic position.

•Integrate detailed surface geologic data with subsurface seismic and well data along two representative transects.

•Develop a regional picture of in situ stress distribution

•Develop integrated model of fracture distribution in space and time.

Scope of study

Progress to Date

Results to dateThere are four different episodes of fracturing. Fracturing occurred under different conditions and from different causes.

iv

Results to dateNot all stratigraphic units are affected by all four events.

iv

Results to dateNot all fractures record the presence of fluids.

iv

Results to dateIntegration of structural geometry, fracture distribution and geochronologic data yields a qualitative picture of where and when fractures developed that explain these variations in fracture distribution.

Cross sections by A. Duncan

Results to dateFurther refinement of these qualitative models using seismic data, thermal data and conservation of area principles allow a quantitative model of the evolution of the Brooks Range foothills over time.

Seismic data provided by Western Geophysical; interpretations by A. Duncan

Results to date

Cross sections by A. Duncan using LithoTect software

Determining how much material has been eroded in any one location allows refinement of where petroleum generation may or may not have occurred.

eroded

iv

Results to dateThe fractures most likely to be effective migration conduits are those that form during hydrocarbon generation

Results to date Set 1 fractures probably formed parallel to maximum compressive stress, in the foreland of the fold-and-thrust belt.

Where ≥overburden

Results to date

Where ≥overburden

Consequently:•Predicting the orientation of the maximum horizontal stress can predict orientation of set 1 fractures.•Depth of fracturing is in part a function of overburden

Results to date

by A. Kleck

Orientation of Shmax

Results to date

by A. Klek

Orientation of Shmax

Results to date

Set 1 fractures will only occur when horizontal stress exceeds the vertical stress.

The longest borehole breakouts occur in three Sv ranges:

- ~ 15 – 35 MPa

- ~70 – 100 MPa

- ~ 115 – 135 MPa

Breakout Length vs. Sv

(wells unsorted)

0

20

40

60

80

100

120

140

160

0 50 100 150 200 250

Breakout Length (m)

Sv (M

Pa)

Breakout length (m)Sv

(Mpa

)

14 wells, 130 data points

Results to date

Sample Count vs. Sv

0 2 4 6 8 10 12 14

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

105

110

115

120

125

130

135

140

S v (M

Pa)

Count (#)

•Largest number of breakouts occur in similar SV ranges.

- ~20-25 MPa

- ~ 80 MPa

- ~120 Mpa

Results to date

Due to unconsolidated sediments?

Due to overburden and/or stratigraphy?

Plans for next year•Complete quantitative model for each transect•Complete regional stress study, including:

•relationship of stratigraphy to Set 1 fractures•a map of regional Sv distribution•a map to depth of critical Sv.

•Prepare results for publication.

ANY QUESTIONS?