American Oil and Gas Reporter - January 2012 - 88

Oil & Gas Shales
The objective of geological steering
depends on the section of the well. In the
build section, where the deviation increases
from the kickoff point until the well enters
the reservoir, the goal is to steer the well
so that it enters the reservoir at a desired
inclination and direction. In the lateral
section, the goal is to position the well's
path to optimize well bore exposure to
the reservoir.
These goals have been achieved consistently through interpreting real-time
LWD measurements, gamma ray in the
build section, and gamma ray combined
with resistivity in the lateral section. These
LWD measurements were selected by
evaluating the log response characteristics
within and adjacent to selected target
zones of the Bakken Middle Member and
Three Forks formations.

well characterized, the LWD log response
was predictable under most conditions
observed.
The LWD resistivity tools have multiple
transmitter-receiver spacings and multiple
frequencies. The resistivity measurement
from each spacing and frequency responds
differently to a resistivity interface located
away from the well bore. Since the nature
of the resistivity interface is known from
the offset well logs, multiple resistivities
can be leveraged to obtain a profile to
help maintain the well's position within
the target interval at a distance from the
interface.
During drilling, an experienced
geosteering field engineer compared the
measured LWD responses with the modeled synthetic responses to determine the
position of the well's path within the geological sequence. The engineer also referenced all other relevant information,
such as cuttings sample observations from
the mud logging geologist, to support the
geosteering interpretation.
The resulting geologic interpretation,
which incorporated observed differences
between expected and measured LWD
responses, combined with additional
drilling-related data, was communicated
to NPE to allow the drilling and geology

LWD Resistivity
Electromagnetic wave propagation resistivity tools delivered the standard deepsensing LWD array wave resistivity measurements. Because these measurements
were similar to wireline resistivity measurements, the LWD logs were correlated
with similar wireline logs to locate important geological features. Because the
wave propagation measurements were
FIGURE 2

Prewell Model of the Projected Landing Point (Holland No. 9-19H)
GAPI

CHMM

CHMM

RT_RHTE

1,000

RSPH_M
9,690

RMPH_M
RDPH_M

Modeled Resistivity

100

Upper Bakken

RDAL_M

10

Modeled Resistivity Response

1
9,720

GAPI

ORR_S

Gamma Ray/ROP

120

RVD

9,750

80

40

Modeled Gamma Ray Response
0

feet

9,690
9,780

Lower Bakken
9,720

Planned Well Trajectory
9,750
TVD

Projected landing point
at 9,806 feet TVD based
on initial geologic model
and well plan

9,810
9,780

Three Forks target interval
identified by red lines

9,810

0

40 80
120
Gamma Ray

1

10
100
Resistivity

1,000

9,760

9,840

88 THE AMERICAN OIL & GAS REPORTER

9,920

10,000

10,080

feet

team to make time-critical decisions efficiently about adhering to or modifying
the well plan.
The team was able to adjust the drilling
plan as the horizontal well was drilled,
using actual well bore trajectory data and
LWD logging measurements. In consultation with NPE, the team incorporated
interpretations to reconcile the local geologic model with real-time data, allowing
the well bore position to be maintained
within the target zone.
Refining Results
Real-time LWD data acquired from
within the zone of interest not only were
correlated with the synthetic model, but
also were back-correlated with previous
measured data from the same well as the
trajectory moved upstructure or downstructure within the target formation. All
decisions regarding changes to the well
trajectory considered BHA capabilities,
the original directional well plan, and
completion requirements in consultation
with NPE. Continuous control of the well
bore trajectory delivered reduced tortuosity
and dogleg severity, leading to quicker
well bore completion and production.
LWD data and forward modeling interpretation results were delivered at the
well site and remotely, using secure Webbased applications. This enabled realtime collaboration from directional drillers,
geologists, and other experts in multiple
locations. A final post-well analysis depicts
log evaluations and further refinement of
the local model to obtain the best fit, resulting in a close-modeled approximation
of the actual measured formation properties.
The enhanced model was incorporated
into the plan for the next well, delivering
an increasingly refined result. Observations
of the results are compiled and documented
for use as a future frame of reference to
further optimize drilling procedures.
Directional drilling, measurement- and
logging-while-drilling (M/LWD), and forward-modeling steering services, combined
with the extensive experience of the NPE
drilling team, have enabled consistent positioning of the horizontal wells in zone.
Success in this geological well positioning
partnership has been achieved through
close teamwork and timely communications, while continually building on the
knowledge gained from each well to accumulate an ever-increasing understanding
American Oil and Gas Reporter - January 2012

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