Hydraulic fracturing has demonstrated its value in terms of production uplift for the Clair Field from the first hydraulically fractured well on the Clair Phase 1 Platform. The Clair Ridge Platform, the second phase of the Clair Field development, has been on production since 2018. The Ridge area of the Clair Field is a naturally fractured part of the reservoir. The natural fractures provide productivity drive to the Ridge producers. However a few wells that did not encounter sufficient natural fractures, have delivered production results below expectations. Consequently, this caused increased interest in hydraulic fracturing to protect the base and provide additional production uplift.
Hydraulic fracturing in naturally fractured reservoirs poses certain challenges and uncertainties for the design and execution. The candidate well was selected based on absence of natural fractures, poor matrix quality and low initial production rates. The well has been pre-produced, which further complicated the stimulation scope. Enhanced fracturing modeling with the use of 3D cube from full field model aided stimulation design by integrating hydraulic fracture placement with mapped faults and reservoir unit boundaries.
Fracturing offshore as a wellwork campaign is an intensive and complex scope. The inefficiencies in fracturing after the upper completion on platforms not specifically designed to support hydraulic fracturing operations cause delays to operations and realizing the production benefits. A key challenge for the Clair Ridge Platform was to build on the standalone fracturing operation on the Clair Phase 1 Platform and deliver a similar intervention-based stimulation, but while a fast-paced drilling program was ongoing, which posed a big challenge for simultaneous operations (SIMOPS). This paper documents how the first multistage fracturing on the Clair Ridge Platform was performed in parallel with active drilling and production, significantly increasing the intervention complexity. Operationally, the fracturing set up involved wireline for gas lift valve replacement, coil tubing (CT) for sleeve manipulation and clean out between stages, a stimulation vessel for pumping and a well clean up package to separate solids during clean out and initial flowback.
The well productivity index post-stimulation has increased five-fold during transient period and three-fold stabilized. Chemical tracers were used to enhance the understanding of zonal contribution to production. Proving the feasibility of ‘offline’ offshore stimulation during active drilling, the project has in turn revealed many challenges. These challenges are documented along with detailed lessons learned on optimizing SIMOPS for future operations. New insights include considerations on design and hydraulic fracture placement in naturally fractured reservoirs, with lessons learned for managing pressure dependent leak-off. It opens an opportunity to hydraulically fracture zones of higher fracture density to further enhance production for the wells on the Clair Ridge Platform.
