Abstract

During workover and completion operations, even a small overbalanced hydrostatic pressure can result in a significant loss of fluid to the formation, especially in high-permeability formations. This situation becomes even more drastic in depleted reservoirs, horizontal wells, or in zones that have been previously fractured and packed. Controlling fluid loss into the formation is of critical importance during overbalanced workover operations to minimize near-wellbore (NWB) damage invasion by the completion fluid, which can yield problems associated with poor wellbore cleanout and loss of hydrocarbon reserves. In addition, fluid loss can increase costs associated with rig time and treatments devoted to restore the initial condition of the formation. In many hydrocarbon fields in southern Argentina, controlling fluid loss before NWB cleanout treatments is challenging because it can cause pressure differential sticking of the coiled tubing (CT) and/or inability to pump the treatment into the desired interval. This paper presents the successful field application of a novel solids-free fluid-loss (SFFL) system during wellbore cleanouts in the Cerro Dragon oilfield, which is located on the west side of San Jorge Gulf (SJG) basin in the Chubut Province of Argentina.

The SFFL system relies on water-soluble polymer that decreases matrix permeability to aqueous fluids, limiting leakoff into treated zones. This polymer immediately adsorbs to the surface of the rock, eliminating the need to shut the well in. In addition, this system does not require the use of breakers or a cleanup stage to reestablish hydrocarbon production once the workover operation has been performed. Laboratory test data show the capability of the material to control fluid leakoff and achieve high levels of regained permeability to hydrocarbons. Traditional techniques to minimize fluid loss use solids or viscous pills, although it has been amply documented that these systems can damage the formation if not properly removed after the treatment.

To date, about 200 treatments have been performed with this novel SFFL system. The paper discusses field results from the application of this system during overbalanced workover operations in Argentina, including the job design and post-treatment results. This system has been proposed for returning partial and total loss to full circulation in overbalanced operations, such as (1) lost-circulation events occurring during cementing, fracturing and drilling, (2) well intervention cleanouts by CT and hydraulic workover (HWO), (3) gravel packing, (4) replacement of artificial lift equipment (i.e., electrical submersible pumps), and (5) overbalanced tubing-conveyed perforating (UTCP).

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