Colloidal-Dispersion Gel in a Heterogeneous Reservoir in Argentina

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 174704, “CDG in a Heterogeneous Fluvial Reservoir in Argentina: Pilot and Field-Expansion Evaluation,” by D. Diaz and N. Saez, YPF; M. Cabrera, InLab; E. Manrique, Consultant; and J. Romero, M. Kazempour, and N. Aye, Tiorco, prepared for the 2015 SPE Enhanced Oil Recovery Conference, Kuala Lumpur, 11–13 August. The paper has not been peer reviewed. The Loma Alta Sur (LAS) field is a multilayer fluvial sandstone reservoir in the Neuquén basin of Argentina. Reservoir heterogeneities and an adverse mobility ratio (30-cp oil) led to an early water breakthrough soon after water injection started. Colloidal-dispersion- gel (CDG) injection was considered a viable strategy to improve oil recovery in the field. LAS-58 CDG Pilot Summary The CDG pilot was implemented in the LAS-58 injector located on the northeastern side of the field. LAS-58 is an irregular pattern that began water injection in 2002, showing an early water breakthrough. The operator estimates that after 3 years of water injection in the LAS-58 pattern, cumulative secondary oil recovery is only 5.48% of original oil in place (OOIP). The LAS-58 pattern includes 10 producers: six first-line producers with well spacing ranging from 138 to 164 m and four second-line producers. The first tracer-injection program was implemented in March of 2003, 3 months after initial water injection in the LAS-58 injector. The fastest tracer breakthrough was observed in offset producer LAS-18 (50 days). However, the amount of tracer recovered in LAS-18 and LAS-26 was below 1.5% of the total injected. Producer LAS-49 showed the second-fastest breakthrough but with a cumulative tracer recovery of 4%. Each of the CDG-injection phases was followed by water injection at similar injection rates. The total volume of CDG injected (62 179 m3) represented 3.06% of the pore volume of the LAS-58 pilot area. Phase I consisted of a small injection volume intended to test CDG injectivity and did not affect pilot oil-production response but definitively contributed to adjusting the polymer concentration used in the pilot through Phases II and III of CDG injection. The main observation after Phase II of CDG injection was a very distinctive change in the injection profile of the LAS-58 injector. The water-injection flow paths were diverted into the middle (Mandrel 2) and bottom (Mandrel 1) zones of the pay zone because of the reduction in injectivity in the thief zones located at the top (Mandrel 3) of the reservoir. In October 2007, the incremental oil production for the 10 offset producers was reported as 133,292 bbl, with a reduction in water production of 406,949 bbl.