American Oil and Gas Reporter - August 2015 - 111

SpecialReport: Rockies Activity Profile

Urban 3-D Survey Keys Drilling Success
GREELEY, CO.-The city of Greeley
is situated on the northern end of the
Denver-Julesburg Basin's Wattenberg
Field in what is referred to as the "sweetest
of the sweet spots" for hydrocarbon production from Niobrara chalks and the
Codell Sandstone. While horizontal drilling
has been active throughout Weld County,
very little activity has occurred historically
inside Greeley city limits, partly because
of a lack of subsurface control to effectively and safely drill Niobrara and Codell
horizontal targets.
Mineral Resources Inc., a privately
held oil and natural gas producer based
in Greeley, developed a plan to acquire
high-resolution 3-D seismic data within
city boundaries for the purpose of drilling
horizontal wells to Niobrara and Codell
targets. To this end, MRI conducted one
of the largest urban 3-D seismic programs
in the country in the spring of 2013.
Months of extensive preplanning were
required by both the operator and contractor to complete the acquisition of the
23 square-mile survey in this challenging
urban environment.
Seismic data processing employed
state-of-the-art static corrections and
noise-reduction technologies to help prevent the smearing of small faults and
structures at the target level. Interpretation
involved detailed 3-D kinematic structural
analysis and framework modeling of the
Niobrara and Codell formations, since
understanding structural dips and the
nature of the listric faulting at target level
were paramount in placing laterals. In
addition, seismic reservoir analysis using
neural network inversion technologies
identified reservoir sweet spots within
the Niobrara and Codell intervals for optimizing fracturing staging and completion
designs.
The operator now is using the interpretation results from the 3-D survey in
its successful horizontal drilling program.
To date, MRI has drilled more than two
dozen extended-reach horizontal wells
within the Greeley survey area. The acquired data are allowing the operator to:
* Correctly land and target Niobrara
and Codell objectives in terms of staying
in the hydrocarbon layer while drilling

lateral sections;
* Navigate and plan around geologic
faults, which could throw the well out of
zone and significantly impact ultimate
production;
* Significantly reduce the number of
rig days and drilling costs by drilling the
wells to plan; and
* Improve resource and asset management going forward.
The success of this project can be attributed largely to the real-time, integrated
approach taken between early planning
and design, transparency with the community, adaptive 3-D acquisition, and
hands-on processing and interpretation.
This methodology helped to guarantee
high-quality data coming from the field
and an overall smooth operation.
Wattenberg Field
The Wattenberg Field (Figure 1) is
one of the largest overpressured, basincentered oil and gas fields in the Rockies
with respect to total proved reserves,
areal extent, and wells drilled. The field
spans more than 2,000 square miles primarily in Weld County, but also extending
into parts of Adams, Denver, Boulder,
Broomfield and Larimer counties.
Discovered in 1970 by a vertical well
drilled into the Dakota "J" Sandstone,
Wattenberg continues to be one of the
most active fields in the country. The
high activity level even after 45 years of
almost continuous development can be
attributed to the sheer size of the field,

the use of advanced 3-D seismic methods,
horizontal drilling techniques, improvements in completion technologies, and
aggressive Niobrara and Codell workover
programs.
Wattenberg lies at the intersection of
the north-to-south trending axis of the
Denver Basin, with a northeast-to-southwest trending zone of elevated heat flow
associated with the extension of the Colorado Mineral Belt into the basin. This
intersection of elevated heat flow and the
relatively deep burial of the sedimentary
section have resulted in very large volumes
of hydrocarbons being generated within
the field's boundaries. Most of the shallow
section is pressured normally and contains
hydrocarbons, but the Niobrara and Codell
intervals within the middle of the productive section are extremely hydrocarbon-saturated and overpressured.
The structure within the Wattenberg is
dominated by a series of northeast-trending
wrench faults associated with Precambrian
basement tectonics, which have had recurrent movement throughout the Cretaceous. Deep within the section, these faults
are vertical with strike-slip motion, but
split into an increasingly complex polygonal
system of listric normal faults within the
Niobrara and Codell formations. This
structural complexity can make horizontal
pad drilling within the Niobrara difficult
with regard to remaining within the zone.
Seismic technology is critical to imaging
this complex fault pattern, accurately placing horizontal wells, managing drilling

FIGURE 1
Map of Wattenberg Field and D-J Basin Stratigraphic Column
Typical
Depth

Pay

Wyoming
Parkman SS

3,500 ft

Pierre Shale

Nebraska

Sussex (Terrry) SS
Pierre Shale
Shannon (hygiene) SS

4,300 ft
4,800 ft

Pierre Shale

Front Range

By Jack Wiener,
Collin Richardson
and Tagir Galikeev

Niobrara A

Wattenberg

6,800 ft

Niobrara B
Niobrara C

Kansas
Source Rock

Colorado

Source Rock

Ft. Hays Limestone
Codell Sand
Carlile Shale
Greenhorn LS
Graneros Shale

7,100 ft

J Sand
Skull Creek Shale

7,600 ft

Dakota Sand

7,800 ft

AUGUST 2015 111
American Oil and Gas Reporter - August 2015

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