First Thermo-Responsive Polymer Field Evaluation in a High Temperature Reservoir of Golfo San Jorge, Argentina. Promising Results for Cost Optimization in a Polymer Project

Abstract

This paper presents the results obtained during the first thermo-responsive polymer field evaluation carried out in Pampa del Castillo – La Guitarra field located in Golfo San Jorge basin, Chubut province, Argentina. For the selected reservoir conditions, two thermo-responsive (TR) polymers with the same backbone and different moieties content (TR 1 and TR 2) were designed as alternatives to the conventional HPAM polymer currently injected in the field. TR polymers are aimed to be injected at low concentration and low viscosities under surface conditions and are characterized by an activation temperature. Below this temperature threshold, they behave like regular HPAMs whereas above it they behave like associative polymers. In contrast to HPAMs, higher resistance factors are obtained with increasing temperature beyond the activation threshold, which would be achieved at reservoir conditions. TR 1, TR 2 and a selected HPAM were injected in the same well and same layer, under the same conditions during a polymer injectivity test (PIT) in order to compare their performances. The evaluation was done in a multilayer, 80°C - temperature reservoir showing permeabilities around 20 mD. This reservoir had been waterflooded for 32 years before polymer injection started. The test was carried out using a compact polymer injection unit (PIUC) for 60 days involving TR 1, TR 2 and HPAM injection at different concentrations and flow rates, previously defined to target similar mobility reduction (Rm – also called Resistance Factor, ReF) according to coreflood experiences. Fall-off tests were run prior to, during and after polymer injection to assess changes in the well injectivity. Along with the operation, laboratory tests were carried out on site to monitor water and polymer solution parameters. TR 1 and TR 2 polymers showed good injectivity, stable rheological properties and good performance during the injection test at all concentration values and flow rates. Well head pressure (WHP) recorded with TR 2 was higher than with TR 1, in accordance with the number of thermo-responsive moieties in each polymer formulation. TR polymers demonstrated to be purely shear-thinning while HPAM showed shear-thickening behavior in near wellbore conditions. These results indicate promising cost reduction that can be achieved through a concentration cut-back of 67%, while sustaining similar resistance factors under reservoir conditions. The present article will elaborate on the first results of an injectivity test of thermo-responsive polymer technology conducted in Argentina.