Alternate Path
Technology
Higher production
from gravel-packed
wells
Applications
Introduction
■
Bypass premature bridging in
vertical intervals longer than
40 ft
■
Frac pack in unconsolidated
sands or high-permeability
zones
■
Gravel pack of horizontal
intervals as long as 8000 ft
■
Gravel pack in deviated wells
■
Separate completions of two
intervals in one trip
■
Control of gas or water influx
during production
Services based on Alternate Path technology provide shunts with nozzles on
the outside of the gravel-pack screen.
These shunts create an alternative
flow path, allowing slurry to bypass
premature bridging and fill the voids
below. In an Alternate Path operation,
gravel placement proceeds initially in
the standard packing mode until
screenout. A pressure buildup occurs
after screenout and forces the slurry
to flow through the shunts and exit
through the nozzles to the first available void. Packing continues until all
voids are filled and a final screenout
occurs. With voids eliminated, the
gravel pack is tight and complete.
Alternate Path technology is used
in the AllPAC† standard gravel-pack
service, the combination of AllFRAC†
and Schlumberger frac and pack services, MZ packer zone-isolation service,
and Horizontal AllPAC and AllFRAC
services for horizontal wells.
Benefits
■
Improved gravel packs over
long intervals
■
Improved production from
tightly packed annulus and
perforations
■
Efficient gravel packing of
long horizontal, deviated and
vertical intervals
■
Higher conductivity in
fractured intervals
■
Reliable screen protection
for high-rate wells
■
Longer completion life
■
Single-step multizone
completions
■
Higher cash flow and
increased reserves from
higher production
Features
AllPAC service
AllPAC service applies Alternate Path
technology to standard gravel-pack
operations. Nozzles every 6 ft on the
shunt allow slurry to exit below a
Excellent diversion over the
entire perforated interval
■
No need for premium screens
in openhole horizontal
completions
50
■
Multiple Alternate Path†
screen designs
40
Annular bridges bypassed
by gravel slurry
■
Various sizes of shunts and
exit ports
■
Shorter pumping times
AllFRAC service
By using larger shunts that allow for
increased pump rates, Alternate
Path technology is applied to frac
and pack operations. Fractures propagate throughout the interval, not just
above a premature bridge, and proppant is placed along the entire interval. Fractures are tightly packed for
maximum conductivity. Multiple zones
can be fractured and packed during a
single run, saving the cost of multiple
completions. AllFRAC technology has
played an integral part in the recordsetting production from one operator’s
wells in the Gulf of Mexico.
Alternate Path technology improves gravel-packing efficiency.
■
■
premature bridge, filling remaining
voids. In one study, AllPAC completions averaged 42 lbm/ft of gravel
placed behind the casing, compared
to 15 lbm/ft placed by conventional
completions. AllPAC service operates
in vertical, deviated or horizontal
wells, either cased or openhole. More
gravel placed means more complete
perforation packing and fewer annular
voids. The result is a more reliable
completion with higher production.
Sand behind
the casing
(lbm/ft)
30
20
10
0
Conventional
gravel pack
AllPAC
gravel pack
MZ packer zone-isolation service
Horizontal AllPAC and AllFRAC services
AllPAC and AllFRAC services are also
used in multizone single-trip completions to control water or gas influx
during production. To extend Alternate
Path technology to this application,
one or more opposable-cup isolation
packers are added. Shunt tubes pass
through the packer cups to enable
gravel packing over multiple intervals.
The MZ packer creates a barrier
between the screen and casing. At the
end of gravel-packing operations, the
shunt tubes and nozzles are packed
off. The packed shunt tubes act as
linear flow cells, preventing fluid flow
through the shunts and effectively
isolating the intervals from each other
during production. Completions can
include fracturing one interval (usually the upper zone) and gravel packing the second interval (usually the
lower zone).
Multizone completions have
resulted in substantial cost savings
and higher production compared to
conventional completions. This higher
production results from minimizing
the use of fluid loss pills in a singletrip completion.
When gravel packing horizontal
wellbores using conventional technology, significant problems are often
encountered: silt and shale sloughing,
premature bridging from high leakoff, filter-cake cleanup problems, and
difficulty regaining permeability. Gravel
packs in these wells are often poor or
incomplete, exposing long intervals of
screen to erosion or plugging.
Completions with Alternate Path
technology avoid the conventional
problems because the pack quality is
excellent, even over long horizontal
intervals. Horizontal AllPAC and
AllFRAC services use nondamaging
carrier fluids, remove filter cake during gravel placement and maximize
productivity. Wells completed using
this technology have a high productivity index because sloughing and
premature bridging are bypassed and
the entire interval is packed. With a
complete gravel pack, ordinary wirewrapped screens, which are more
resistant to plugging than premium
screens, can be used even in intervals
as long as 8000 ft.
This NODAL* production system analysis for a formation with 50-mD permeability compares production
from perforations with 50% (Curve 1) and 100% packing (Curve 2).
4000
Inflow
3000
Pressure
(psig)
2
2000
1000
1
0
0
1000
2000
3000
4000
5000
6000
Production (BOPD)
7000
8000
9000
10,000
Shunts on the outside of the screen provide a slurry path
to void areas below premature bridging.
AllPAC applications
AllPAC case history
AllFRAC case history
■
Vertical intervals greater than
40 ft long
■
Openhole intervals with silt
and/or shale streaks
■
High-permeability unconsolidated intervals
■
Intervals with high rates
of production
■
Deviated wells
In a circulating gravel-pack treatment,
AllPAC technology was used to ensure
complete packing of all voids. After
36 min of treatment, the pumping rate
was reduced. At the end of the treatment, all remaining voids were packed
for 2 min at a rate of 2 bbl/min. In this
short period 675 lbm of proppant were
delivered to the annulus, ensuring the
tight and complete annular packing
that was critical to the success of this
high-rate well. The resulting skin of
1.1 is a significant improvement to
the industry average of 8 for openhole
gravel packs in shaly reservoirs. Specifications for this well and treatment
were
A STIMPAC* frac and pack treatment
to bypass damage was performed
using the AllFRAC service over a
long interval containing laminated
pay zones. Without Alternate Path
technology, a premature screenout
would have occurred after 42 min of
treatment in these zones, at the 3-ppa
stage, resulting in a less than optimal
treatment. The AllFRAC service
allowed the slurry to bypass the premature bridge, diverting it through
the shunts to frac and pack the lower
zone. Changes in temperature recorded
by gauges in the wash pipe during the
operation confirmed treatment success. Specifications for this well and
treatment were
AllFRAC applications
■
Vertical intervals greater than
40 ft long
■
Openhole intervals with silt
and/or shale streaks
■
High-permeability unconsolidated intervals
■
Intervals with high rates of
production
■
Deviated wells
■
measured depth (MD): 12,275 ft
■
true vertical depth (TVD): 5800 ft
■
deviation: 75°
■
interval length: 300 ft
■
proppant design: 8000 lbm
MZ packer applications
■
proppant pumped: 8000 lbm
■
Single-run completions of
multiple zones with zonal
isolation
■
carrier: 4% ClearFRAC* fluid.
■
Control of gas or water
during production
■
Multizone completions
■
MD: 8806 ft
■
deviation: 15°
■
interval length: 133 ft
■
proppant design: 42,000 lbm
■
proppant pumped: 37,500 lbm
■
carrier: YF100LG fracture
treatment gel.
Eccentric and concentric AllPAC and AllFRAC shunt tube geometries are shown for cased hole applications.
Horizontal AllPAC applications
■
Intervals as long as 8000 ft
■
Heterogeneous intervals with
silt and/or shale streaks
AllPAC
■
Intervals with areas of high
leakoff
Pipe OD
■
1 in.
Wellbores having difficulty
regaining permeability or
filter-cake cleanup problems
Pipe OD
Screen
shunt ring
Screen
shunt ring
1.5 in.
93
■
AllFRAC
Openhole wellbores drilled
with oil-base fluids
Screen
OD
Screen
OD
0.5 in.
0.75 in.
Fishing OD
Joint
connector
OD
Joint
connector
Fishing OD
Joint
connector
OD
AllPAC technology provided a low-skin completion in this high-rate well.
6
2500
Rate
5
2000
2500
6
2000
5
4
4
1500
3
1500
1000
Pressure
(psi)
2
500
1
0
0
33
1000
35
36
38
3
Rate
(bbl/min)
39
2
Pressure
500
1
0
0
0
7
15
22
29
36
42
Time (min)
AllFRAC technology diverted the slurry past the annular bridge to the lower zone, resulting in a complete frac and pack of the interval.
Upper gauge
10,000
12,840
16
14
12
10
8
6
4
2
0
8,000
12,860
Pressure
(psi)
12,880
Surface
pressure
6,000
Rate
4,000
Concentration
2,000
12,900
0
0
12,920
10
20
30
40
Time (min)
50
Rate
(bbl/min) or
concentration
(ppa)
60
12,940
190
8000
Temperature,
lower gauge
7500
12,960
Bottomhole
pressure, upper
and lower
gauges
7000
12,980
Pressure
(psi)
6500
170
Diversion
160
6000
150
5500
13,000
140
Temperature,
upper gauge
5000
13,020
130
4500
0
Lower gauge
180
10
20
30
40
Time (min)
50
60
Temperature
(°F)
Complementary fluids
and services
The following fluids and treatment solutions are available for
wells completed using Alternate
Path technology.
■
ClearFRAC fluid—This polymerfree viscoelastic (VES) surfactant-based carrier fluid is used
for gravel packing, fracturing
applications and horizontal
completions.
■
ClearPAC* fluid—A polymerfree VES fluid, it is especially
designed for gravel-pack operations in weighted brines and
elevated temperatures.
■
OILPAC* fluid—An oil-external
emulsion, this fluid is used for
well-control operations in circulating packs using oil-base
drilling fluids.
■
HEC fluids—Hydroxyethylcellulose polymer-based fluids
are used as gravel-pack
carriers.
■
Xanvis® fluid—This fluid is
a biopolymer gravel-pack
carrier fluid.
■
Multizone completion case history
In a multizone completion, an AllFRAC
frac and pack treatment on the upper
interval and AllPAC gravel-pack treatment on the lower zone were conducted sequentially. After the fracture
treatment, returns were taken to force
all the slurry to the lower zone for the
gravel pack. The AllPAC shunts limited the rates below the MZ packer,
preventing fracture propagation in the
lower zone. A shale interval prevented
growth of the fracture downward.
This multizone completion technique
produced oil from the lower zone that
would have otherwise remained in
place. Specifications for this well
and treatments were
■
MD: 8608 ft
■
deviation: 25°
■
length of interval: 155 ft
■
proppant design: 85,000 lbm
■
proppant pumped: 95,000 lbm
■
carrier: low-guar borate crosslinked
water-base polymer fluid.
The flexibility of the shunt configurations enabled successful treating and fracturing of the upper zone and
gravel packing of the lower zone, which was close to a water contact.
MudSOLV* filter-cake removal
service—This engineered cleanup technique enables filter-cake
removal concurrent with the
sand-control treatment.
MudSOLV service maximizes
the filter-cake removal treatment. Filter-cake removal is a
key factor in optimizing the
production from or injection
into openhole gravel packs.
0.7 in.
27 ft
MZ packer
140 lbm/ft
6000
30
A
5000
Pack
B
20
4000
Well
pressure
(psi)
25
Fracture
3000
15
2000
10
1000
5
0
0
0
20
40
Time (min)
60
Rate
(bbl/min) or
concentration
(ppa)
Horizontal completion case history
An openhole circulating gravel pack
was pumped after the slurry was
mixed. Before the slurry reached the
openhole section, the return rates
began to decrease. A premature bridge
formed in the annulus, making it necessary to divert the flow through the
shunted screen. After the flow bypassed the area of high leakoff, the
returns increased until the well was
completely packed. Specifications
for this well and treatment were
■
MD: 5000 ft
■
deviation: 90°
■
length of interval: 1200 ft
■
proppant design: 45,000 lbm
■
proppant pumped: 40,000 lbm
■
carrier: MudSOLV filter-cake
removal treatment fluid.
Changes in downhole conditions do not jeopardize the success of a completion using Alternate Path technology.
10
6000
Pressure
Rate in
Rate out
Sand concentration
5000
9
8
7
4000
Pressure
(psi)
6
Return rate
increasing
6-ppa concentration
5
3000
Rate
(bbl/min)
4
2000
3
Start shunting
2
1000
Slurry at crossover
ports at 52 min
1
0
0
0
10
20
30
40
50
60
70
80
Time (min)
Horizontal AllPAC and AllFRAC services provide technology for complete gravel packing of horizontal intervals as long as 8000 ft.
Transport tube
93
QUANTUM*
packer
Packing tube
Gas-bearing layer
Hydrocarbon-bearing layer
Water layer
www.connect.slb.com
TSL-4551
May 2001
©Schlumberger
*Mark of Schlumberger
†Marks of ExxonMobil Corp; technology licensed exclusively to Schlumberger
®Xanvis is a registered trademark of Monsanto Company.