-
The
Ultrashort-Radius Radial System
W. Dickinson,
SPE,
Petrolphysics Ltd.,
R.R. Anderson,
*
Bechtel Natl. Inc., and
R.W. Dickinson,
Petrolphysics Ltd.
Summary.
A group of interrelated horizontal
drilling and completion technologies,
collectively called the
ultrashort-
radius radial
sys?
tem (URRS), was
developed and is being progressively applied
in the field. Multiple radials can be placed
at the same level and on
multiple
levels. Three-dimensional (3D) surveying is
supplied. Horizontal completions can be provided,
including lOO%-
fili gravel
pack?
ing, in-situ
electrolytic perforation and cutting, and
flexible sand barriers (FSB's). Initial field
applications were in unconsolidated formations.
Introduction
The URRS was
developed, tested, and applied over the past
10
years. This paper reviews the
drilling and completion technologies,
presents results from initial field
applications, and outlines ongo?
ing research. With this technology,
more than 27,000 ft [8230 m]
was
drilled and more than 500 horizontal radials
were placed by
use of various
embodiments of the system.
radius and
90° bend of the whipstock, the drill head enters
the for?
mation
horizontally. The drillstring is not rotated.
These separate components of the
URRS-
the drillstring, the
mo?
tion controller, and
the whipstock-
combine to propel and
to con?
trol the motion
of the drillstring into, through, and out
of the
whipstock. resulting in
three load conditions of the drillstring.
The first URRS component related to
propulsion and control is
the
drillstring (radial tube), which is propelled
out of the vertical
workstring by
the fluid pressure within the workstring.
The second component is the motion
controller (Fig. 4) on the
tail of
the drillstring, which acts as a hydraulic
restraint. In essence,
it is a piston
with external seals that slide within a special
smooth
borehole portion of the vertical
workstring. The high-pressure water
pushes on the top of the motion
controller, and water is trapped
between it and the
high-
pressure seal at the bottom of
the work?
string. Water can
escape only through a central orifice within the
controller (Fig. 4). The result is
a hydraulic restraint, or brake,
on
the forward motion of the 1l,4-in. [32-mm]
drillstring.
The third URRS component
of
the propulsion and
control sys?
tem is the
whipstock, which bends the drillstring from
vertical to
horizontal.
Fig.
5 shows the loads on the drillstring that result
from propul?
sion and
restraint forces. In its passage into,
through, and out
of
the
whipstock, the drillstring is subjected to axial,
internal-pressure,
and bending loads.
In Section A of the drillstring (above
the high-pressure seal), the
drillstring stresses are below the
elastic limit. In Section B, where
the
drillstring is below the high-pressure
seal and within the whip?
stock, the drillstring stresses
exceed the elastic limit and the
drill?
string deforms
plastically. Because the drillstring is
internally
pressurized and is
constrained by rollers and slides within the
whip?
stock, it does not
buckle while it is being bent. In Section C,
the
1l,4-in. [32-mm] drillstring exits
the whipstock horizontally. There
it
is under only axial and internal-pressure loads.
Again, the stresses
are below the
elastic limit.
The pressure on the
water drilling fluid in the system not only
propels the drillstring, but also
drills the horizontal borehole in the
formation. To drill the formation, the
water drilling fluid is acceler?
ated through the conical-jet drill-
head nozzle, creating a conical
shell
of
water
particles traveling at 800 to 900
ft/sec
[244 to 274
m/s].
Sy.t.m
The objective for the URRS is to
provide an extended wellbore
radius
by means of multiple radials from a vertical
wellbore (i.e.,
to effect an extended
completion or extended piped perforations).
These radials may
be
placed in one layer or multiple
layers, de?
pending on
reservoir thickness and vertical communication.
Figs.
I and 2 show two arrangements of
multiple radials in multiple layers.
The choice of radial length, number
of radials, and radial array
is a
function
of
the reservoir
properties. A study to optimize these
radial parameters for various
reservoir conditions is currently un?
der way. The specific variables
included in this study are reservoir
thickness, vertical and horizontal
permeabilities, oil properties, well
spacing, outer-
boundary
reservoir pressure, gravity drainage,
ther?
mal and nonthermal
processes, and presence
of
impermeable
partings within
the reservoir. The choice of radial length and
ar?
rangement generally is
unique to each reservoir.
Sy.t.m
Proc
?????
and
The basic URRS uses an
erectable whipstock lowered downhole
by a 41/2-in. [1l4-mm] workstring
into an underreamed cavity or
hydraulically slotted opening of 22-in.
[56-
cm] diameter. The whip?
stock (Fig. 3) is designed for use in
a 7-in. [178-mm] casing. The
drillstring is made of 1lA-in.
[32-mm] electric-t;t:sistance welded
tubing (A-606). The drillstring may
be
provided from a coiled-
tubing
rig or it may be fabricated
on site from 30- to 40-ft [9- to 12-m]
tubing joints.
A hydraulic
drill head is welded to the nose of the first
joint of
the drillstring (radial
tube).
If
the drillstring
is fabricated on site, .
subsequent
30- to 40-ft [9- to 12-m] joints of drillstring
are welded
by automatic computer-
controlled welding on the rig floor to form
the drillstring. A hydraulic motion
controller that regulates rate of
penetration (ROP) is welded to its
tail.
As the drillstring is
fabricated, it is lowered inside the vertical
4V2-in. [114-
mm]
workstring. The nose (drill head) of the
drill?
string enters a
high-
pressure removable seal at the
top of the whip?
stock. The
seal provides the bottom closure
of
the workstring.
Hence, the 1
lA-in.
[32-mm] drillstring is fully contained
within the
4V2-in. [1l4-mm]
workstring at the outset of drilling (Fig.
3).
A wireline cable attached to the
tail of the drillstring runs to the
surface within the workstring and
passes through the top closure
of
the workstring. Thus, a long sealed chamber
containing the
1lA-in. [32-mm]
drillstring and its connecting cable is created
by
the 41/2-in. [1l4-mm] vertical
workstring.
Water drilling fluid at
8,000 to 10,000 psi [55 to 69 MPa] is
pumped into the long vertical
workstring at the surface with a con?
ventional fracture pump. The drilling
fluid is then pumped down
the
workstring where it enters the drillstring.
The internal water
pressure of the
drilling system propels the drillstring through
the
high-pressure bottom seal and
through the bending and confining
slides and rollers
of
the whipstock. Traversing the 12-in.
[30-cm]
y Inspection Div.?
Mare Island Naval Shipyard.
Copyright 1989 SOCiety of Petroleum
Engineers
Fig. 6a shows a schematic
of the conical jet. At the top of the
figure is a standard collimatedjet
nozzle. The addition of fixed vanes
within the nozzle causes a conical
shell of high-
velocity water
par?
ticles to form a
conical jet (Fig. 6b). The size of the horizontal
bore?
hole is established by
the twist of the vanes, which in turn controls
the angle of divergence of the cone of
water particles. Figs. 6c and
6d show
vanes for two different conical angles.
Fig. 7 shows water jets resulting
from various degrees of vane
twist in
I-microsecond flash photographs of a
collimated jet and
two different
conical jets. The conical angle is not
affected by
drilling-fluid pressure.
These conical jets function at both ambient
and elevated backpressures. At higher
backpressures, cavitation does
not
appear to be an important cutting mechanism. Fig.
8 shows test
results of
submerg
ed conical jets at ambient and
elevated backpres?
sures
(2,000 psi [13.8 MPa]).
The conical
jets cut through unconsolidated
and
consolidated for?
mations
and produce a radial borehole with a diameter
of about
4 in. [10 cm] or more in
unconsolidated formations; a
smaller?
diameter hole is
produced in hard rocks. Its ROP is 6 to 60
ft/min
247
SPE
Drilling Engineering, September 1989
Radial
Completion System
PERSPECTIVE
Casing
Zone
Radial Bores
Radiol
Bores
Pay
Zone
.
'-111=-1
' .
-III=-
-
-
-II,
111-
11-'
Radial Bore
-I
II
I
~III=
I
_III
Flexible.
Sand
III=-
1_
=n
Barner
1==111==111
I,
P
1
I-I
1
'
JII~
111-
II
--:111==111
III=-,
,,-
I
m:
J
11_
I
111=-1
Section A
Fig.
1-URRS.
[0.03 to 0.3
m/s]
in unconsolidated formations and
about
Ih
ft/min
[0.003 m/s]
in hard rocks
(e.g., granite). Typical oil-bearing rocks
(e.g., sandstones and limestone) are
penetrated at
1,4
to 10
ft/min
[0.003 to 0.05
m/s].
Whipstock. Fig. 3
show
s tie hasic wiipstocj
configugation, a dou?
bly
curved inverted question mark. Inside the URRS
whipstock is
a series
of
rollers and slides that causes a
progressive deflection
and bending
of
the 1lA-in. (32-cm]
drillstring as it moves through
the
whipstock.
Tie wiipstocj is ield in
place hy downiole anciog jaws engag?
ing the well casing. The anchoring
jaws are set by rotating the
41h-in. [114-mm] vertical workstring.
To erect the whipstock, the
workstring is raised about 1 ft [30
cm] by the blocks. The resulting
vertical motion erects the whipstock.
The workstring and whipstock
are held
erect by a set
of
hydraulic cylinders at the wellhead
that
maintains constant tension.
After each radial placement, the
steps
age gevegsed. Tie
wiip?
stock can then
be
de-erected, rotated,
and re-erected downhole
witiout
losing its calihgation. A gygoscope is used to
set tie wiip?
stock azimuth
for each radial. Thus, multiple radials can
be
placed
SPE
Drilling Engineering. September 1989
Fig. 2-Multlple-radlal completion.
248
Cable
Motion Controller
Drill String
Working
String
High Pressure,
Removable Seal
Direction
of Flow
W-f---
Motion
Controller
t
-H+---
Drill String
Section A
High Pressure Seal
I
I
Anchoring
Jaws
Casing
Underreamed
Zone
Whipstock
with
internal rollers
and
slides to bend and confine
the
Drill String
Drill
String
~~J[]
cl
A:
I
S
ec
t
ion
Drill String stresses
are
below the
elastic
limit
I
Whipstock
Assembly
Drill String
Radial Bore
Hole
Fig. 3-URRS.
I
I
Section
B:
Drill String stresses
exceed
the elastic
limit
1
Section
c:1
Drill String
stresses are
below the
elastic limit
Fig.
5-Stresses
on drillstring.
f:
--
IT
II
t,-=:-
~----
Flowrate determines
~-
I[
..
l
Ii
' [
)1
r
i
f
II
'
Drill
String speed
-- Control Orifice
19mm
a)
LEACH AND WALKER CONFIGURATION
III
II
::1!
IJ
Motion Controller
Direction of Motion
Drill
String
VANE INSERT
ill
1I1I
I
co,,!,:2~cItEJ
OF CUTIING
FLUID
b) CONICAL JET NOZZLE IN
SECTION
il
II
[-1
-
Vertical
Tubing String
Trapped Water
I I
Seals
c)
VANE USED IN 30° CONICAL JET
NOZ
ZLE
II~I
__
--Flow to Conical Jet
Fig. 4-Penetratlon control while
drilling.
SPE Drilling Engineering.
September 1989
d) VANE USED IN 10°
CONICAL JET NOZZLE
Fig.
6-Conical
jet nozzle.
249
Linear Voltage
Differential Transformer
Sensors
Vertabrae
Tool Cross-Section
Excitation
. Source
I
I
~
.
Seal
To ROC
Tool
Electrical Schematic
Fig. 9-ROC tooi.
DC
Power
Cable
Perforator Body
c)
30
0
Conical
Jet
nozzle at 0.4
MPa
Fig.
7-Water
jets.
Perforator
Nozzle
Electrolyte
Path
Perforation
Radial
Tube
I
A
ll
te
sts run
in
Sienna
Whit
e
Granit
e
fo
r 15
secands, with a
10'
Con
ical
Je
t
Noz
zl
e,
at
8000 psi
Line
Pressure
50
::I
40
E
-
-
30
'tl
50
40
Perforator
Centralizer Fins
Coaxial
Electrical
Braid Conductor
Fig, 10-Eiectrochemlcal perforator.
>
0
E
CI)
30
a::
CI)
CI)
20
10
E
'0
>
::J
~
0
5
at different
azimuths downhole without having to trip the
whipstock
back to the surface
between each successive radial
.
3D
Positional Survey.
After each radial borehole is
drilled
,
the
1
lA-in. [32-
mm] drillstring can be
surveyed to determine its trajec?
tory with special flexible radius-of-
curvature (ROC) survey tools
designed to pass through the 12-in.
[3D-cm]
(or smaller) bend
radius
of the drillstring
.
The ROC survey tool was developed to
provide
both plan
(azimuth)
and profile
(up/down trajectory) data. It
is
pumped down the workstring and enters
and passes through the drill?
string as a wireline tool.
The tool (Fig.
9)
resembles an
animal
back?
bone and has long slide wires placed
at each quadrant that move
within
vertebrae attached to a flexible
,
torque-resistant, wire-cable
backbone.
The slide wires actuate very pre
cise
sensors that meas?
ure the
movement of each slide wire separately,
translating direct?
ly into
the curvature of the ROC tool and, in tum, of the
drillstring.
SPE Drilling
Engineering. September 1989
20
10
0
0
Standoff Distance / Nozzle
Diameter
Fig. 8-Backpressure and
standoff tradeoffs.
250
?.
.
10