American Oil and Gas Reporter - July 2018 - 52

SpecialReport: Horizontal Wellbore Construction

Approach Optimizes Horizontal Drilling
By John Willis,
Diego Tellez,
Randy Neel,
Greg Caraway,
Derek Adam
and John Rodriguez
HOUSTON-Occidental Oil & Gas
Corp. (Oxy) has systematically optimized
well designs and drilling practices as part
of a continual horizontal drilling improvement process in the geologically
complex and operationally challenging
northern Delaware Basin in southeastern
New Mexico.
Salt intervals, natural flows, injection
zones, depleted zones, interbedded formations with varying unconfined rock
strengths, hard rocks, downhole vibrations,
regulatory requirements and logistics
combine to create a difficult drilling environment. Extensive engineering is required to achieve a high level of drilling
performance.
Oxy began horizontal drilling operations in southeastern Eddy County, N.M.,
in 2012, and drilled 179 horizontal wells
in the area by the end of 2017, targeting
as many as eight stacked intervals. Vertical
depths for the 179 wells range between
5,000 and 12,000 feet, and lateral lengths
have evolved from 3,000 to 10,000 feet.
Optimizations have included well designs,
drilling practices, downhole vibration
control, drilling fluids, cementing and
downhole tool quality control.

The improvements to drilling practices
and techniques are highly intertwined.
They include:
* Using rotary steerable systems on
complex back-builds and side-builds,
eliminating sliding friction and controlling
well paths along adjacent wells;
* Reducing vibration, enhancing bit
and depth-of-cut (DOC) designs, and developing drilling parameter road maps in
the intermediate hole section;
* Enhancing bit designs to improve
tool-face control in the curve hole section;
and
* Managing friction to efficiently
drill the lateral section and run casing to
total depth.
Initially, well paths were controlled
by steerable motor systems. In 2015,
RSS technology was adopted to accommodate the more complex well paths of
multiwell pad development and minimize
collision risk on adjacent wells. On early
wells, shallow "nudges" were used to
separate wells. Although the angle change
was small, the doglegs at the kickoff
point were severe enough to create serious
rod wear on beam pumps. RSS allowed
the well paths to be controlled with lower
doglegs.
As lateral lengths increased over time
in the horizontal drilling program, RSS
became more valuable in the laterals. As
friction increases with lateral length,
sliding to control the well path with steerable motors becomes more difficult. RSS

FIGURE 1
RSS and Steerable Motor Usage by Year
800

120%

700
100%
600
Feet (Thousands)

80%

60%

400
300

40%

Percent of Feet Drilled

% Feet drilled
500

200
20%
100
0

10%
2012

2013

2014

2015

2016

2017

Years
Total Footage

Steerable Motor Footage

52 THE AMERICAN OIL & GAS REPORTER

RSS Footage

% RSS

% Motor

increases the drilling speed and keeps
laterals in the target zone more consistently.
Initially, the goal was to use RSS for
single-run curves and laterals. As shown
in Figure 1, RSS use increased rapidly to
the point where it drilled 90 percent of
all horizontal footage in 2017. However,
an RSS capable of high build rates in the
curve has been challenged to perform
well in lateral, prompting Oxy to switch
back to a steerable motor for the curve
section. That has led to improved curve
and lateral drilling times, even with wells
transitioning to longer laterals.
Intermediate Section
Interbedded soft and hard rock layers
make bit vibrations particularly damaging.
Bits can be destroyed in a very short
time if parameters are not optimized. The
drilling team began working to minimize
stick/slip and lateral vibration in the intermediate hole section in 2015, focused
on reducing whirl and optimizing stabilizers. Vibration analysis led to design
and operating changes that have diminished whirl damage on bits and stabilizers
in 81⁄2- 97⁄8- and 121⁄4-inch sections.
In 121⁄4-inch holes, extreme oscillations
were observed on surface drill string
torque when drilling shallow formations.
Downhole sensor data enabled the nature
of the dysfunction to be better understood.
Severe stick/slip was occurring while
drilling in the Castile formation, an anhydrite with interbedded salt layers. Frequency analysis on the collected data
showed the stick/slip was strongly correlated to the BHA's first and second torsional modes. The conventional benthousing steerable motor BHA was replaced
with an RSS BHA, since analysis indicated
the RSS BHA's higher rotational speeds
would avoid torsional harmonics. This
change increased average ROP by 64
percent and reduced the average number
of bits from 2.0 to 1.1.
The results of the RSS BHA versus
conventional BHA are displayed in Figure
2. However, the data indicated that some
damage was still occurring from whirl,
axial and torsional vibration in the intermediate hole. Downhole shock, vibration
and bit rotating speed data showed that
stick/slip also was still occurring. Consequently, mechanical solutions were implemented such as bit depth-of-cut control,

American Oil and Gas Reporter - July 2018

Table of Contents for the Digital Edition of American Oil and Gas Reporter - July 2018