Optimizing the Performance of Produced Water Chemical Treatment Following CEOR Polymer Breakthrough

Abstract

Chemical enhanced oil recovery (CEOR) plays a major role in sustaining production, extending the life of field and improves the recoverable reserves which is of economic benefit. The injected polymer will eventually propagate to the production wells where it is co-produced with production fluids. The presence of polymer in the back produced water may increase the residual oil levels and suspended solids in the produced water. This causes production systems bottlenecks, have a detrimental effect on water treatment processes, and increase in Oil in Water levels higher than admissible specs for discharge or reinjection. Several CEOR projects are introduced to producing fields where an established water treatment process already exists. These processes are initially designed to perform under a set of fluid and operating conditions. Polymer breakthrough can change the back produced water characteristics and impact the performance of the process. Upgrading of processes may require substantial investment. Chemical additives are widely considered as pragmatic alternative to improve water quality to desired levels. The selection of chemicals is very important as there are other associated challenges to be considered e.g. of the use of inorganic coagulants such as polyaluminum chloride (PAC) has been shown in studies to generate significant amounts of viscous sludge with low dry solids creating, sludge handing and equipment issues in the field. In this study, a new product combination has been developed to solve some of the drawbacks of traditional chemical such as sludge production while maintaining the performance of treatment. The composition of the product was determined through series of lab experiments and using design of experiments (DOE) methodology. The experiments were initially performed using a synthetic mixture of 400 parts per million (ppm) of hydrolyzed polyacrylamide (HPAM with hydrolysis degree ~ 30%) in saline water. The results were benchmarked to PAC and shown to produce a lower amount of sludge (25-50%) with the same performance in the same range of dosage (300-400 ppm). The sludge generated from the new combined product was also less viscous compared to the benchmark product. The investigation also revealed that a composition containing both inorganic/organic coagulant and cationic polymer improved performance. Results were validated with a field sample containing approx. 300 ppm of HPAM polymer. It was found that to generate less sludge and remove maximum total suspended solids, complete removal of polymer is not required. This new product offers several benefits including a reduction in the operating costs (product dosage is about half of benchmark product, polyaluminum chloride), reduction in the chemical footprint, improves the operational efficiency of the water treatment process and allows to operate within their environmental specifications.