1. Reservoir Characterization
of the Mancos and the Lewis Shale Gas Plays :
Review and Comparison
GLGY 703 – Readings in Geology
Supervisor : Dr. Per Kent Pederson
By :
Yulini Arediningsih
April 28, 2011
University of Calgary
2. Outline
Background
Objectives
Geology and Reservoir Characteristics
Comparison
Conclusion
3. Objectives
To review reservoir characterization
particularly the Mancos shale and the Lewis
Shale within the Rocky Mountain Region.
To provide a summary of key reservoir
features of the Mancos Shale gas reservoirs
4. Background
The Lewis and Mancos Shales are significant
contributor in gas production of most Rocky Mountain
basins.
The Lewis Shale gas play is among the main shale
gas producers in the lower 48 states.
The Mancos Shale is the second largest shale gas
producers in the Rocky Mountain Region
Well defined characteristics on the Lewis Shale.
In contrast, geological, geochemical and other
reservoir parameters of the Mancos Shale are still not
well defined.
10. Stratigraphic from GR log of the Mancos Shale
members over the Douglas Creek Arch
(Cole et al, 1997).
11. The Members of the Mancos
Shale
Members /
Prairie Canyon Juana Lopez Lower Blue Gate Tropic - Tununk
Properties
Dense, non-fissile, dark Consists of dark gray calcareous
Both are made up by detached mudstone and
gray claystone with mudstone with interbeds of silt to
siltstone succession that are both embedded
Lithology scattered, light gray silt very fine sand laminae containing
within the Mancos Shale in northeast Utah.
laminae and bivalve silt–filled burrows and marker
High in quartz content.
fragments. bentonite beds.
Thickness 1200 ft < 100ft 2000ft 500-825ft
Porosity % 2.8 – 11.6 2-5 No data No data
Permeability 0.001 – 0.427 md No data No data No data
0.65 (Estimated from
Ro % 0.65 – 1.5 No data No data
overlying rock unit)
More than 2.0 that might prove to be 'sweet spots' for shale
TOC wt% 1-2 3
gas
Potential for natural fracturing due to high
Natural
quartz content in their siltstone – sandstone Potential for natural and induced fracturing
fracturing
units
12. Comparison
Similarities :
Depositional environments
Compared to other Paleozoic prolific shale gas deposits,
both contain much lower organic matter and much siltier
lithology
Both Lewis and Mancos have four members
Commingled gas production from other sandstone units.
Differences :
Lithology
Thickness
Bentonite Huerfanito Bed in the Lewis
Porosity
13. Parameters Lewis Mancos
Various lithology as interbedded
Rock lithology Sandy siltstone mudstone, siltstone, and very
fine-grained sandstone
Four members : The Prairie
Four members : the Ute, the
Canyon, the Juana Lopez, the
Members Navajo City and the First and
Lower Blue Gate and the Tropic-
Second of the Otero
Tununk
Thickness (feet) 1000-1500 Reaching 4000
2-8
Porosity % 2-5
Permeability effective gas = 0.1 - 0.00001
Na
(md) Average = 0.0001
0.45 to 1.59 with an average of 1 – 2, type II to mixed type II-III
TOC wt%
1.0 kerogen.
Maturity (Ro) 1.66 – 1.88 0.65 - 1.5
Always commingle with
Always commingle with Dakota
Production Mesaverde and or Dakota
and or Castle Gate sandstones
sandstones
14. Conclusion
The Mancos Shale is a thick series of fine grained rocks, consisting
of interbedded claystone, siltstone, and very fine-grained sandstone,
deposited in clastic shoreline to offshore marine environments during
the Late Cretaceous.
The most potential interval for development of the Mancos Shale
gas reservoir is the upper part of 3000-3500 ft thick, which largely
represents the Prairie Canyon Member.
Distribution of Ro values suggests mature areas for oil and gas
throughout the Mancos interval. The Upper Mancos Shale is typically
mature for oil and thermogenic gas whereas the lower part is mature
to over mature for oil in most of the basin.
Amount of humic (terrigenous) fraction of organic matter contained
in the Mancos Shale is controlled by location of deposition of the
lithologic sequences with respect to the vegetated shorelines of the
Sevier belt.
Natural fractures are present and identified in the Mancos Shale
15. Some of the References
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