The Effect of Back-Produced EOR Polymers on Scale Squeeze Efficiency

The potential for process upsets on the production side of back-produced polymers used for enhanced oil recovery (EOR) applications is fairly well understood and is the focus of many research programs currently. It is thought that polymer present in produced water can not only cause separation issues but can also be a problem in heat exchangers and other topside processes. In assets where inorganic carbonate and or sulphate scale is also an issue, the effect of having EOR-type polymer in the near-wellbore area and in produced fluids is less well understood.Where scale squeeze campaigns (bullhead deployments of scale inhibitor (SI) chemicals into the production section of the reservoir) are employed to protect the wellbore and production equipment from scaling, adsorbed polymer in the near-wellbore area has the potential to occupy vital adsorption sites, which the squeeze chemical (phosphonate or polymer based) might not subsequently have access to. This competitive adsorption process was shown here, via coreflood experiments, to significantly shorten the squeeze lifetime of the widely applied inhibitor diethylenetriamine penta(methylene phosphonic acid) (DETPMP) at near minimum inhibitor concentration (MIC) levels when compared to a core previously flooded with degraded hydrolysed polyacrylamide (HPAM) EOR polymer.In addition to the squeeze lifetime studies, the efficiency of the scale inhibitor performance was also found to be affected if EOR polymer was present in the produced water. In static inhibitor performance bottle tests, the EOR polymer alone appeared to show some degree of inhibition performance, but below a level required for effective scale management; However in combination with the squeeze inhibitor at near MIC levels, the inhibition efficiency was negatively impacted by the presence of degraded HPAM EOR polymer. During dynamic tube blocking tests, the inclusion of even low levels of HPAM (2.5ppm) were shown to reduce the differential pressure build up suggesting scale inhibition or reduced adhesion to the coil.To understand the impact on inhibition performance, changes in scale morphology were investigated by environmental scanning electron microscopy and energy dispersive X-ray (ESEM-EDX) analysis. On addition of HPAM alone or with <MIC SI concentrations, HPAM appears to have the ability to influence the morphology into a variety of smooth surfaced forms based on spherical geometry. When only scale inhibitor is present the tubular scale morphology appears to show a less smooth, more striated surface indicating SI crystal growth blocking mechanisms occurring. From these observations, it is clear that HPAM impacts the way scale grows, especially at lower SI concentrations and hence impacts the mechanism by which DETPMP can function to prevent scale nucleation and growth.Finally, squeeze treatment design software was used to investigate the longevity of the scale squeeze application as a direct result of reduction in adsorption of the scale inhibitor caused by EOR polymer competitive adsorption and lower scale inhibitor performance.This study represents the first comprehensive review of both inhibition performance in the presence of an EOR polymer and the implication to field treatment volumes and associated costs of scale management in a field under HPAM flooding.