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.
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 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.