Summary
A major Middle East operator has applied expandable tubular solutions for
water shutoff and zonal isolation in fractured carbonate reservoirs. In this
paper, we review the operator’s experience with the implementation of this
emerging well technology. Expandable tubular solutions have proven successful
in terms of installation reliability, isolation of fractures, and zonal
isolation without cement to segment horizontal wells.
Case histories highlight the benefits, risks, and performance of expandable
tubular completions. Post-installation production performance proves the
viability of mechanical inflow profile control for better management of
unwanted production of water in fractured carbonate reservoirs.
Introduction
A major Middle East operator faces the challenge of increasing water
production from maturing oil fields. Carbonate reservoir fields with either
natural water drive or waterfloods can benefit from fracture shutoff with the
objectives of increasing oil recovery, reducing water production, and improving
the sweep efficiency of waterflood operations.
Past completion practices have been either unreliable or invasive on the
reservoir and have failed overall to provide the capability to manage water
production over the life cycle of the well. Wells with barefoot completions
have watered out because of water breakthrough through conductive faults and
fractures. The most common challenges encountered are:
-
Water influx from fractures or water
bearing formations (Fig.1).
-
Early injection water breakthrough in
producer wells and water short-cutting between water injector and producer
wells through fractures (Fig. 2).
To control unwanted water production, a shift from openhole completions
toward wellbore segmentation is underway. A completion approach with horizontal
cemented liners based on selective perforations has been used. The main
limitations of this approach are:
-
At the time of completing the well, it
is as yet unknown which fracture will produce unwanted water.
-
Intervals with low oil saturation are
not perforated and consequently not swept.
-
In fractured reservoirs where loss of
circulation is frequently encountered, cementations have often failed.
Selectivity, which is the main reason for a cemented liner completion, is
therefore often not achieved.
Fracture shutoffs have been carried out with scab liners as depicted in
Fig. 3. Zonal isolation is provided by external casing packers (ECP).
The main limitations of this approach are:
-
ECPs are short seals. If the formation
behind the ECP is fractured, there will be seepage behind the seal through the
formation, in which case the seal is ineffective because of its short
length.
-
Access to the toe of the well is
challenging because of the reduction in hole diameter.
-
In many cases, scab liners have leaked,
as shown in Fig. 4. A fracture shutoff was carried out in a horizontal
water injection well. A memory-production log was obtained to determine the
injection profile. The temperature log confirms that there has been channeling
and injection of water into a fracture behind the scab liner.
-
Retrieval of scab liners has proven to
be technically very challenging and time-consuming. Therefore, wells with
leaking scab liners cannot be easily worked over.
Expandable Tubular Solution
Expandable tubular solutions were originally developed to extend well depth
while maintaining a larger borehole diameter (Dupal et al. 2001). Such a
product is usually referred to as an openhole liner (OHL). The technology is
based on running a liner, placing cement, and then expanding the liner across
the borehole section into the previous casing to form a liner hanger (Filippov
et al. 1999).
The main value drivers for applying expandable tubular solutions in
carbonate reservoirs are as part of the completion (for water shutoff) and as
part of a well constriction (for loss curing). The operator decided to
introduce expandable tubulars for water shutoff. Instead of cement, the
operator used swelling elastomers to achieve zonal isolation in the open hole
(Van Noort et al. 2002; Braas et al. 2003). The liner is expanded to seal the
annulus by energizing an elastomer between the expanding casing and the
formation. In addition, the elastomer swells in contact with produced water,
oil, or both. This expandable tubular shutoff solution is called open hole clad
(OHC). A schematic of a fracture shutoff with an OHC is shown in Fig. 3. Unlike
an OHL, an OHC does not include a tieback into the previous casing.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
4 December 2004
- Revised manuscript received:
3 April 2006
- Manuscript approved:
3 April 2006
- Version of record:
20 March 2007
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