Chemical Solutions to Handle Viscosified Back Produced Water in Case of Polymer Flooding

Abstract

Abstract Polymer flooding is used as a secondary or tertiary recovery mechanism to enhance oil production and increase oil reserves. In such situations, part of the injected polymer will be back produced at the topsides at different ratios depending on the injection mode and along field life. The side effects of polymer flooding on the topsides process chain are identified as manageable trouble regarding oil/water separation, and major issues at the water treatment stage. The presence of polymer in the produced water increases the viscosity and the severity of the emulsion. Literature dealing with viscosified water has already highlighted decreases of efficiency of water treatment technologies such as hydrocyclones, flotation, generating inadequate water quality for produced water reinjection (PWRI). A common way to optimize flotation on field is to inject additives. But the polymer impedes the action of conventional chemicals used in O&G Production. Chemicals usually help to improve the water quality, regarding constraints of PWRI. This paper focuses on chemical approach along the separation and water treatment chain in case of back produced polymer. For this study, we used HPAM, a high molecular weight polyacrylamide commonly used in EOR. Previous works on conventional water treatment additives have shown a high consumption of chemical to clarify viscosified water, which is not economically practicable. Therefore, we proposed to explore another approach, first taking care of water quality upstream at the separation stage, then pursuing on chemical optimization at the water treatment stage. At first, a lab methodology for separation studies was developed to generate a thin emulsion with controlled degradation of the polymer, simulating the characteristics of the back produced viscosified water on field. A screening of demulsifiers was carried out on emulsion containing 10% oil and synthetic polymer back produced water (up to 500 ppm HPAM). These tests have shown that water quality can be improved at the separation stage, at conventional dosage at lab scale. The remaining oil in water for 10% initial oil, depending on the residence time, is maintained in the range of few tens to few hundreds ppm. Water treatment optimization reference case was then based on few hundreds ppm of remaining oil. For water treatment studies, oil in water emulsions were prepared by mixing oil with synthetic or real viscosified water (up to 500 ppm HPAM) with an ultra-turrax homogenizer. Different types of clarifiers ranging from 50 to 100 ppm were evaluated. These tests have shown that water quality can be improved using a combination of adequate additives. These bench lab results were confirmed on a lab conventional technology, and could be further evaluated in field trials for an integrated solution.