Abstract

19° API gravity oil with a viscosity between 150 to 200 cp is produced from the “El Corcobo Norte” and “Cerro Huanul” fields (550 active producer wells and 330 active injector wells) located in the Neuquen basin, Argentina. The reservoir is an unconsolidated sandstone reservoir that has been producing since 2005 by combining two techniques: cold heavy oil production with sand (CHOPS) and conventional waterflooding. Water injection began approximately one year after the start of production of oil, and while an excellent production response to the injection well was observed, the continuing sand production generated deep wormholes that allowed for direct communication between the injector and producer in some wells, resulting in the total loss of oil production.

Beginning in 2011, different remediation techniques were tested from the injector wells to repair the “pipeline” to the producing wells, with variable results. The original remediation program consisted of two steps: 1) a treatment to reconstitute the porous matrix (TRPM) and 2) a conformance water-control treatment (WCT), which was not as effective and was eliminated in the following remediation treatments. TRPM allowed the operator to put back into production wells that had been shut in, and its design evolved to help reduce costs and continue the wells’ reactivation.

To achieve an estimated ultimate recovery (EUR) factor of 50% (it was at 35% between the primary and secondary recovery), an injection project including an alkali, surfactant, and polymer (ASP fluid) treatment was implemented to improve the fluid sweep efficiency in a mature area of the field having high water cuts (85 to 90%). This project included drilling infill wells to go from an inverted seven-spot to a direct five-spot pattern, reducing the acreage from 60 to 20 acres (Ac). In 2013, the infill wells were completed without CHOPS; instead, a fracpack with proppant coated with a curable liquid resin (CLR) resistant to high pHs (i.e., the ASP fluids) was used to help prevent a possible collapse of the reservoir in the near-wellbore and entrapment of the progressive cavity pump when the ASP fluid front passed through as it would remove the residual oil that holds the sand grains together. To date, this fracpack treatment appears to have achieved the objective.

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