American Oil and Gas Reporter - January 2012 - 92

Lessons Learned
The LWD log responses observed for
the wells targeting the Bakken Middle
92 THE AMERICAN OIL & GAS REPORTER

Member were characterized in a similar
fashion as the Three Forks wells. The 15foot thick target interval below the tight
limestone maintains consistent, nondescript
gamma ray and resistivity characteristics
below the limestone, continuing down to
the lower Bakken Shale.
The lack of character through the lower
half of the Middle Member formation
presents a challenging interpretation.

Therefore, the cleaner gamma ray and
slightly higher resistivity of the limestone
directly above the target interval are
utilized as benchmarks to solidify the
geosteering interpretation.
The resistivity measurements begin to
separate and increase according to their
respective diameters of investigation as
the well bore approaches the contrast in
resistivity between the target interval and

FIGURE 5A
Real-Time Structural Interpretation Conducted at the Well Site
(Middle Bakken Formation)
OHMM

OHMM

Vertical Depth Correlation
10,860

Real-Time Resistivity

API

RT_RHTE
RSPH_A

10

RMPH_A
RDPH_A
RDAL_A

Real-Time Resistivity Measurements
OHMM

RT_RHTE

Modeled Resistivity Response

Modeled Resistivity

10,890

RSPH_M

100

RMPH_M
RDPH_M

10,920

GRC_S

RVD

Gamma Ray

120

SLBD_A
GRCA_A

90

ROP_A
60

Real-Time Gamma Ray (Green) versus Modeled Gamma Ray & ROP

30

10,950

0
10,840 feet

ActualW
ActualW

10,880
10,980

Upper Bakken
10,920

Middle Member target
interval identified by red lines

TVD
11,010

Well Bore Trajectory

10,960

11,000

Real-Time PZS Structural Interpretation

Landing Pl.
11,040
11,040

Lower Bakken
0

30 60 90 120
Gamma Ray

1

10
Resistivity

11,000

100

12,000

13,000

14,000

15,000
MD

16,000

17,000

18,000

19,000

feet

FIGURE 5B
Correlation Displaying LWD Measurements Character
As Utilized for Geosteering Decisions
API

OHMM

OHMM
Real-Time Resistivity

Upper Bakken
11,000

RT_RHTE
RMPH_A

10

RDPH_A
RDAL_A
RSPH_A

Real-Time Resistivity Measurements
OHMM

11,005

RT_RHTE

Modeled Resistivity

RSPH_M

100

11,010

RMPH_M
RDPH_M

Modeled Resistivity Response
GRC_S

Gamma Ray

120
11,015

RVD

SLBD_A
GRCA_A

90

ROP_A
60

Real-Time Gamma Ray (Green) versus Modeled Gamma Ray & ROP

30
0
10,970 feet

11,020

10,960

11,025

ActualW
ActualW

Middle Member target
interval identified by red lines

10,990

11,000
TVD

Figure 2 displays the prewell geologic
model with the anticipated logging response
along the proposed well path.
After drilling vertically to 8,300 feet
total depth, the PZS service was initiated
to complement geological and mud logging
information for picking the kickoff point.
Building the curve started at 9,280 feet,
using a 2.5-degree bend, PathFinder G2
mud motor, an 83⁄4-inch PDC bit, and 63⁄4inch gamma ray logging and directional
tools. The real-time geosteering technology
was managed by an experienced field engineer on site. Prewell modeling, remote
support during operations, and post-well
analysis were performed in Lafayette, La.
Formation changes were logged and
observed differences to the original model
were used to compute adjustments to
revise the landing point. At an angle close
to horizontal, the well successfully entered
the target zone at 9,805 feet TVD (10,096
feet TD) to reach the 9,808-foot TVD revised landing point, 2.5 feet below the
top of the target clean dolomite within
the Three Forks formation. This compares
with a planned landing point based on
the initial model at 9,815 feet TVD (seven
feet deeper).
Seven-inch casing was set to 10,202
feet, then the lateral producing section
was drilled using a 6-inch PDC bit, 1.5degree adjustable steerable G2 mud motor,
slim (43⁄4 inches) advanced wave propagation resistivity and gamma ray logging
tool, and an MWD positive pulse telemetry
system. While drilling the lateral, the
geosteering field engineer used real-time
gamma ray, resistivity, and directional
data, combined with geological information
from mud logging, to advise NPE on
steering the well within the planned objective, following the dip of the formation
(Figure 3).
The inclination of the lateral ranged
between 89 and 93 degrees, reacting to
the regional dip changes. Accurate well
positioning was achieved by characterizing
measured gamma ray and resistivity response differences between the top and
the base of the Three Forks formation
target interval.
At the top of the target interval, the resistivity is higher with more separation, in
combination with slightly lower gamma
ray measurements at the top versus the
base (Figure 4). Well total depth was
achieved at 17,739 feet MD, 9,725 feet
TVD. Of the 7,643 feet of lateral footage
drilled, 7,214 feet (94.4 percent) of the
well bore was positioned within the target
interval.

11,030

Well Bore Trajectory

11,010

11,020

Real-Time PZS Structural Interpretation

11,035

Lower Bakken
Vertical Depth Correlation

11,030

11,040
0

30 60 90 120
Gamma Ray

1

10
Resistivity

100

13,000

13,500

14,000

14,500
MD

15,000

15,500

16,000

feet
American Oil and Gas Reporter - January 2012

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