Experimental Identification of Permeability Reduction Factors in the Danish North Sea During Produced Water Reinjection

Abstract

Abstract Loss of formation permeability during reinjection of produced water is a challenge which occurs frequently in offshore and onshore oil and gas production. Because of this, production companies need to develop measures to increase the injectivity of wells, such as hydraulic fracturing and acid treatments, which incur additional operational costs of oil production. The risk of injectivity loss is higher in tight reservoirs such as chalk. This study presents laboratory experiments using pressure and temperature controlled core flooding techniques to demonstrate how complete blockage of the chalk core pore space can occur. An analysis of precipitates formed during the injection of mixtures of produced water and seawater into a chalk core from the Danish North Sea was carried out, and an experiment with synthetic produced water is presented to identify the processes in the pore channels as precipitation of salt crystals occurs. The study includes an integrated approach for studying sediments formed during the reinjection of produced water and seawater, namely studying the solid material using a scanning electron microscope (SEM), identifying the type of chemical compounds using X-ray diffraction (XRD), building thermodynamic models based on Extended UNIQUAC, and determining the ionic composition of effluents using High Pressure Ion Chromatography (HP-IC). As a result of the analysis of sediments obtained on cellulose filters and laboratory core flooding experiments, it was established that the main factor in reducing permeability is likely the formation of inorganic sediment in the form of the compound Fe3Si. Understanding this allows the industry to take a more targeted approach to the process of treating produced water before pumping it into wells and reduce costs during well operation.