Modelling the Impact of Low Salinity Waterflooding, Polymer Flooding and Thermally Activated Polymer on Produced Water Composition

It is common that a large volume of hydrocarbons remained unrecovered after primary and secondary recovery. Enhanced Oil Recovery (EOR), as tertiary recovery, plays a key role in recovering additional volumes of hydrocarbons. However, there is little work in the literature on the impact of different EOR mechanisms on the flow behaviour of formation/injected brines and scaling tendencies. The objective of this manuscript is to investigate, by the means of reservoir simulation, the impact of different EOR techniques, namely low salinity waterflooding (LSW), polymer flooding and Thermally Activated Polymer (TAP), for in-depth conformance control, on oil recovery and BaSO ₄ scale deposition. A reactive transport reservoir simulator was used to evaluate the impact of three EOR techniques in the mixing profiles of injected seawater and formation brine, resulting in the precipitation reaction of BaSO ₄, due to the incompatible mixing of formation and injected brines. Three two-dimensional models were considered, a homogeneous and heterogeneous areal model to compare polymer flooding and LSW; and a vertical heterogeneous model to analyse the effect of TAP. Results show that LSW delays and reduces the risk of BaSO ₄ scale deposition at the producer, due to the fact that the concentration of injected SO ₄ ^2- is significantly lower than full sulphate injection seawater. However, LSW results in longer co-production period of Ba ²⁺ and SO ₄ ^2- ions, due to the fact that Ba ²⁺ stripping is reduced because of the scale precipitation within the reservoir is reduced. Polymer flooding improves the sweep displacement, which delays the onset of scale formation, shortens the co-production period of the scaling ions at the producer and reduces the amount of water produced, hence, reducing the scale risk. TAP injection results in the delay of the injected water breakthrough, which delays the onset of scale formation in the producer; however, it can increase the amount of formation water (hence Ba ²⁺ ions concentration), mainly from the low permeability zones, in the producer. EOR techniques may have a major influence on the evolution of scaling ions in the produced water, which has to be taken into account for an optimum scale management strategy, to maximize oil production.