ABSTRACT:

Seawater was effectively used to viscosify a polymer-free fracturing fluid, Schlumberger's visco-elastic (VES) surfactant ClearFRAC, during a multi-well offshore frac and pack rehabilitation on the matured Eni Agip operated Giovanna field, Italian Adriatic Sea, leading to considerable gas production increase, improving operational efficiency, saving rig and process time and reducing costs. Detailed are the chemical aspects and preparational needs of mixing fracturing fluids with seawater, the operational simplicity and impact of the new seawater based VES fluid system on the fracturing design & job execution and the production results obtained after the 23 frac and pack treatments performed. The initial two-well rehabilitation campaign was extended to a third well workover, when production results verified the excellent performance of the new VES fluid. The first successful use of seawater as the base fluid extended the already proven viability and cost-savings of using a visco-elastic surfactant as fracturing fluid for effective frac and packs of low-to-moderate permeability high clay content formations in the Adriatic Sea. To reduce offshore fracturing costs, the attempt of using seawater as a base fluid is not new, however, earlier field trials in other regions to mix conventional polymer-based fluids on the fly with seawater have not lead to notable success. The visco-elastic fracturing fluid created high fracture conductivities and demonstrated confined fracture geometries in the difficult to treat multi-zone reservoir composed of thinly deposited sand-shale streaks. The fluid's favorable leak-off behavior and proppant-suspension capabilities helped to promote TSO and large fracture widths while containing excessive vertical height growth, thereby avoiding near-by water bearing zones.

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