The Impact of Dissolved Iron on the Performance of Scale Inhibitors Under Carbonate Scaling Conditions

Abstract

The laboratory determination of scale inhibitor (SI) performance under field specific conditions using dynamic or static scale inhibitor tests provides an important method for determining minimum inhibitor concentrations (MIC's) for the inhibition of scale growth. This paper will discuss the ability of small amounts of ferrous iron to dramatically reduce the ability of SI's to inhibit calcium carbonate scale formation under dynamic laboratory test conditions. It has been previously reported that the presence of ferrous ions has an inhibiting effect on calcium carbonate formation under dynamic test conditions, which was confirmed for the brine systems used in this study. However, despite the somewhat milder scaling regime in the presence of ferrous ions, addition of Fe2+ ions to test brines caused the observed MIC's of typical scale inhibitor chemicals to increase more than one hundred fold when tested against calcium carbonate scale. A much less dramatic reduction in SI performance in the presence of ferrous ions was observed for barium sulfate scale formation under dynamic test conditions. Such interference in inhibitor performance can have major implications for the field application of scale inhibitor chemicals, leading to unexpected decline in production. The presence of ferrous ions has been shown to adversely affect scale inhibition of a number of different classes of SI chemicals, including poly(vinylsulphonate) (PVS) which has previously been reported as being iron-tolerant. This paper will describe the results of laboratory studies into this phenomenon, in which the nature and scope of the interference were investigated. Introduction Inhibitor performance in terms of the minimum inhibitor concentration (MIC) or the threshold concentration required to prevent scale is one of the most important aspects for scale control additives, equalled only by the challenge of effective placement and deployment in today's ever more complex production environments. The laboratory test protocols adopted throughout the industry are very similar and are based upon static "bulk" inhibition performance tests and dynamic "tube blocking" inhibitor performance tests. The importance of appropriate laboratory test procedures has recently been discussed in detail.[1] The conventional static "bulk" or "jar" test procedures commonly adopted are related to that described in the NACE standards TM 0197–97[2] and TM 0374–2001.[3] Such tests have been described in many previous papers for both examination of the factors controlling inhibitor performance and for selecting scale inhibitor products prior to field applications. These tests are used routinely throughout the industry for scale inhibitor selection and optimisation studies.[1] In addition to static "jar" tests, dynamic "tube blocking" performance tests are also routinely used for scale inhibitor selection in oilfield environments. Dynamic tests complement static tests by allowing different facets of scale inhibitor activity to be examined. For example, dynamic tests examine activity under much shorter residence times than static tests, and so can be used to highlight differences between nucleation and crystal growth inhibition effects. Dynamic tests also allow for the impact of scale nucleation and growth on the walls of the micro-bore tubing to be assessed under laminar flow conditions. There are a number of benefits associated with dynamic performance tests, which have been described in a number of previous publications as follows[1]:Dynamic laminar flow system, as in oilfield productionExamines growth and blockage of microbore metal coilsSystems can be examined under pressure. This allows for routine testing under;higher temperature conditions (> 100°C),in the presence of bicarbonate ions without loss of pH control Finally, and of more importance for this study, the sealed nature of the dynamic flow tests means that:Examination of systems in the presence of dissolved iron can be more readily achievable than in static tests, provided that feed brines are adjusted accordingly to minimize potential oxidation of Fe(II) - > Fe(III).[4]

The Influence of Maleic Acid Co-polymers on the Growth and Microstructure of Calcite Scale

“…This has been shown both in sophisticated experiments examining additive-mediated growth in high energy synchrotron experiments 20,21 via atomic force microscopy 22 as well as in more conventional static and dynamic experiments similar to those shown here. Similarly Figure 2, taken from SPE 80254, 10 shows the dramatic impact of small concentrations of ferrous iron (FeII) on the morphology and composition of carbonate scales grown in microbore coils under dynamic conditions. Similarly Figure 2, taken from SPE 80254, 10 shows the dramatic impact of small concentrations of ferrous iron (FeII) on the morphology and composition of carbonate scales grown in microbore coils under dynamic conditions.…”

“…This allows for routine testing under; higher temperature conditions (> 100°C), 2,3, 6,9 in the presence of bicarbonate ions without loss of pH control, 2,3,5,8 Examination of systems in presence of dissolved iron is more readily achievable, provided feed brines are adjusted accordingly to prevent oxidation of Fe(II) -> Fe(III) 10 The main disadvantage of dynamic performance tests relates to extremely short residence time, generally of order < 10 seconds. This allows for routine testing under; higher temperature conditions (> 100°C), 2,3, 6,9 in the presence of bicarbonate ions without loss of pH control, 2,3,5,8 Examination of systems in presence of dissolved iron is more readily achievable, provided feed brines are adjusted accordingly to prevent oxidation of Fe(II) -> Fe(III) 10 The main disadvantage of dynamic performance tests relates to extremely short residence time, generally of order < 10 seconds.…”

A 4-year Survey of the Application of an Environmentally Preferred Solid Inhibitor in North Dakota

“…A review of the historical water analysis prior to a failure for each well showed that dissolved ferrous iron is present in the water at about 200 to 300 ppm. It has been reported previously that soluble iron has an adverse effect upon the performance of conventional phosphonate-based and polyacrylic acid polymer scale inhibitors against carbonate scale (Graham et al, 2003, Smith et al 2008, Shen et al, 2011. Due to this relatively high iron concentration, it was surmised that the high rate of failures in the presence of normally sufficient scale inhibitor residuals were due to the effect of iron on the performance of scale inhibitor (Szymczak, et al, 2012).…”

Chemical Qualification and Field Application of a Nondamaging Scale Squeeze Treatment in the Mangala Field

“…• Successful remedial treatment to remove existing scale deposits prior to SISQ application • Preventing drop-out of waxes or other organic deposits in the near-wellbore and production system during the treatment, predominantly by keeping the temperature of injected fluids above WAT • Selection of a non-damaging scale inhibitor product suitable for application in this sensitive reservoir • Evaluation of the likely impact of low levels of produced iron on scale inhibitor performance 3,4 • Developing suitable treatment designs to achieve adequate placement along the full length of Mangala's horizontal wells. [5][6][7][8] The remainder of this paper discusses how these requirements were satisfied for the initial squeeze treatments in the Mangala field.…”