Implementing a Field Pilot Project for Selective Polymer Injection in Different Reservoirs

Abstract Polymer-flood projects with selective polymer injection in different reservoirs within the same injector well has never been a simple task, but it can be achieved. This work explains how. During secondary recovery in several reservoirs (contacted by vertical wells), selective installation at injector wells enables vertical distribution wherever convenient (i.e: reservoirs with a high oil saturation, lower injected poral volumes); such distribution in Polymer-flood projects was not possible since some reservoirs were not completely or effectively swept. A new deep well selective injection system has been developed to be used in multiple reservoirs while preserving viscosity of the polymer solution without mechanical degradation. Thus, injection is increased in those reservoirs with hydrocarbon potential with a low admission of polymer or no admission at all. This device is installed in the well bottom (patent still pending) and has side-pocket mandrels with valves operated by the conventional Slick Line rig. Through the different positions of these valves, the desired flow in each reservoir can be achieved. We are going to introduce the work developed in lab and field pilot in order to prove this development is technically feasible. Different tests have been performed in test benches designed to that purpose, the equipment was manufactured and this new tool was installed in some injector wells. The tool was installed in two polymer injector wells. Reservoirs tests had been previously performed to evaluate injectivity, mainly to dismiss problems (high pressure, skin factor or lack of continuity in the reservoirs). Afterwards, valve combination to achieve target injection rate in each reservoir was defined. This pilot experience was held with a service company in the polymer project located in the Diadema field in the San Jorge Gulf Basin Argentina. The field is operated by CAPSA, an Argentine oil operator with 480 producers and 270 injector wells The reservoir flooded with polymer is characterized by high permeability (500 md average), high heterogeneity (10 to 5000 md), high porosity (30%), very layered sand layers (4 to 12 m net thickness), poorlateral continuity (fluvial origin) and oil of 20° API (100 cp at reservoir conditions). The permeability and reservoir pressure in the reservoirs led us to develop a system with a selective admission and no polymer degradation. The Polymer flooding in Diadema started in October 2007 using 5 injectors (it nowadays includes 35 injectors) with an injection rate of 1000 m3d (it is 3300 m3d today). Polymer solution used produced water (16000 ppm TDS brine) and 2500 ppm of HPAM (22 MDa average molecular weight) reaching to 70 cp of average viscosity of fluid injection. This device enables a regulated polymer solution admission into those reservoirs where it was scarce or inexistent, thus improving injected pore volumes, increasing RF, an economic return, and resulting in the massification of the polymer-flood project.