The Loma Alta Sur (LAS) field is a multi-layer fluvial sandstone reservoir in the Neuquén Basin, Argentina. Reservoir heterogeneities and adverse mobility ratio (30 cp oil) led to an early water breakthrough short after water injection started. After the evaluation of different IOR/EOR methods, the evaluation of Colloidal Dispersion Gel (CDG) was considered as a strategy to improve oil recovery in the field.
CDG pilot started in July 2005 in well pattern LAS-58. Pilot considered the injection of two slugs (≈ 190,000 bbls each) separated by one year of water injection at the same injection rate (≈ 1,000 bbl/d). Injected CDG used 300 ppm of an HPAM and Chromium as a crosslinker with a polymer:crosslinker ratio of 40:1. CDG pilot was concluded in October 2007. Pilot monitoring was supported by a comprehensive injection/production data analysis, tracer and injection profiles before and after CDG injection.
Projected ultimate incremental oil recoveries estimated in 2008 were approximately 62,000 m3 (2.9 % of the OOIP). Incremental recoveries were reasonably validated as October 2014. Oil production response in some of the wells of pattern LAS-58 can be correlated with tracer injection before and after the first CDG slug. These changes were also corroborated by time-lapse injection profiles run over the period of the pilot tests. Most recent injection profiles suggest that possible permeability reduction generated by CDG was removed after several years of water injection. Based on the pilot reassessment, CDG injection is under evaluation in the same and different patterns of LAS field. Ongoing CDG evaluation is supported by detailed laboratory and field scale numerical simulation studies.
This study provides an updated evaluation of LAS CDG pilot validating projected ultimate recoveries, recent laboratory evidences of size distributions of CDG injected, rheologic measurements, and preliminary results of pilot history matching. Lessons learned during pilot evaluation and monitoring strategies will be also presented.