The current article describes waterflooding surveillance techniques applied in El Corcobo Norte and nearby fields, operated by Pluspetrol S.A., in the northeast margin of Neuquén Basin. The main productive target is the Centenario formation, a relatively shallow unconsolidated sandstone reservoir. The API gravity is 19° and the oil viscosity under reservoir conditions is between 150 and 250 cP.
Producer and injector well completion is performed applying the so called CHOPS technique (Cold Heavy Oil Production with Sand), which consists of promoting sand production during completion by producing at high rates. Sand production causes the generation of caverns and “wormholes” that increase productivity/injectivity indexes that are necessary to achieve economical productions. Due to the low original reservoir pressure (30 kg/cm2) and fast decline of primary production, it was necessary to support reservoir pressure from the very beginning of the field's operation. The heterogeneity caused by the CHOPS technique and the high oil viscosity represent a challenge for waterflooding performance. However, important waterflooding response was observed in producer wells. Strong water wettability of the reservoir rock and reservoir continuity favor displacement and volumetric efficiencies.
Waterflooding surveillance relies on strong data acquisition of injection and production, which allows, among others, daily injection/production parameter revision, weekly revision for producer well extraction, monthly revision for rates and VRR (voidage replacement ratio), and processing factors (produced or injected pore volumes a year). With the objective of promoting a homogeneous sweep and lower water cuts in producer wells a strategy was designed to determine specific injection and production rates.
The constant application of this surveillance strategy and constant modification of injection and production regime have allowed to obtain recovery factor as high as 20% in the more mature zones in only 6 years of production and to sustain a production plateau during this time. On the other hand, this continuous modification generates uncertainties for forecasting the behavior of the field production and therefore the ultimate recovery factor.
Additionally, actions taken to increase oil production in the field have led to severe producer-injector channeling issues, which affect negatively in oil recovery and need to be prevented in order to optimize ultimate recovery.
Regarding this topic, empirical limits were defined to avoid channeling between producer and injector, and also remediation techniques were developed to recover channeled wells.