The Role of Lake Levels in Oil Shale Distribution

Y. Bartov, D. Nummedal and R. Sarg

The Colorado Energy Research Institute – Colorado School of Mines

Cole and Others, 1995

Cole and Doub, 1992

Fischer Assay

Study Question: What controls the distribution of oil shale in the basin?

Study approach:Analysis of the basins stratigraphy to identify the controls on oil shale deposits

Saline minerals

W NE

Sq 1

Sq 3

Sq 9

Sq 2

Sq 4

Sq 5

Sq 6

Sq 7

Sq 8

Gamma log signature in the Green River sequence

Sequences in the Green River FmW NE

Chronostratigraphic diagram

W NE

Typical sequences in the Green River Fm

Fresh water lake

Brackish lake

Saline lake

Margin Basin

Onlap position in the sequences

W NE

Subsidence rate

S N

Fresh water

Brackish low stand

Saline lake

High lake level – high salinety

Correlation of oil shale zones

Oil shale position in the sequences

W NE

Lake level

Oil ShaleSandSalt

Mudstone

Lake levels

Oil ShaleSandSalt

Lake level

Oxidation interface

Mudstone

Fresh water lakeLake levels

Lake level

Oil ShaleSandSalt

Lake level

Oxidation interface

Mudstone

Brackish lake Lake levels

Lake level

Oil ShaleSandSalt

Lake level

Oxidation interface

Mudstone

Saline lakeLake levels

Lake level

Oil ShaleSandSalt

Lake level

Oxidation interface

Mudstone

High salinity high lake levelsLake levels

Lake level

Oil ShaleSandSaltOxidation interface

Mudstone

High salinity high lake levelsLake levels

Conclusions

1. The Green River Lake in the Piceance basin experienced numerous lake level fluctuations which are expressed in 11 recognizable sequences.

2. Maximum water depth was at least 300 m during high lake levelperiods.

3. The lake evolved from fresh to brackish to saline. This enhanced water column stratification.

4. Oil Shale distribution in the basin was mostly controlled by lake levels that impact the salinity and the position of the oxidation zone in the water column.