The development of unconventional basins across North America for the past decade initially caused some in the industry to wonder if challenges found in unconventional basins would require new chemistries and technologies. As the basins have been produced and water chemistries evaluated and treated, it has become clear that established scale inhibitor chemistries and methodologies are suitable to treat unconventional scaling scenarios. However, the number of applicable chemistries can be limited as some of the most common scale inhibitor chemistries have been found lacking in iron tolerance. The biggest lesson learned over the course of the past decade has been to not underestimate the role that iron can play as spoiler not only in performance of scale inhibitor chemistries, but also in test methodologies and monitoring techniques. While the need to account for iron in conventional programs has not been taken for granted, the amount of iron produced in unconventional production basins has led to a re-evaluation of just how severely iron in solution can impact scale programs from product testing and selection all the way through to program monitoring. This paper highlights the brine chemistries in major North American unconventional basins, especially regarding iron. Test methods and results from dynamic scale loop and anaerobic static bottle testing will be highlighted as well as the limitations of using field brines in product evaluations. Field observations will be discussed to support the importance of proper product selection as well as monitoring techniques. This subject has implications for the industry as unconventional basins across North America continue to search for program improvements to drive reductions in total operational costs. Additionally, as unconventional basins are developed outside of North America, the lessons learned can be applied to efficiently develop best in class scale inhibitor programs. As appreciation for the impact of high levels of iron on scale inhibitor performance continues to evolve, there is a possibility that a smaller amount of iron tolerant scale inhibitors will limit the treatment options available in unconventional production basins.

Continous injection scale inhibitors are routinely used to control the formation of mineral scales, such as calcium carbonate and barium sulfate, within topside or subsea applications. The development of chemical injection systems to deploy scale inhibitors deep into production wells presents further challenges due to the higher temperature of the injection point. While phosphate esters, phosphonates and polymers constitute the major types of scale inhibitors applied to control scale in oilfield applications, all are known to be corrosive to Low Alloy Steels (LAS). This paper will detail the development of low corrosivity scale inhibitors for downhole systems containing LAS components within the scale inhibitor's flow path. A number of subsea fields have been developed in recent years with wellhead trees containing LAS components, in particular F22 carbon steel. F22 carbon steel has been found to be very susceptible to corrosion attack by scale inhibitors typically used in the oil field. To quantify the problem and work towards a solution, existing products covering all major generic types of inhibitors were evaluated using static immersion corrosion tests at test temperatures ranging from 180°F to 300°F; these tests revealed corrosion rates in excess of 30 mpy for these inhibitors against F22 carbon steel. Initial work involved changes to inhibitor formulations by adjustment of pH or changes to neutralization agents. Unfortunately these changes failed to reduce the corrosion rate to acceptable values. Based on the initial screening work new formulations were developed resulting in very low corrosion rates (<1-4 mpy) in the presence of LAS such as F22, AISI8630 and 1018 carbon steel. Data will be shared which shows that the new scale inhibitor formulations have very similar performance compared to a typical, more corrosive subsea applied scale inhibitor. The new formulations have been qualified for downhole chemical injection through an umbilical and are currently being applied or approved for use at Gulf of Mexico and West Africa fields. Development of these low corrosivity scale inhibitors will allow operators to prevent scale issues in subsea fields without impacting the material integrity of delivery systems containing LAS components.

Metal sulfide scaling issue in the oil and gas production continue to present significant flow assurance challenge. Recently, a novel polymeric chemistry that can effectively control FeS scale deposition in oil and gas production system was reported. However, how to manage finely dispersed FeS particulates at surface disposal facilities and whether this polymer is capable of mitigating ZnS and PbS deposition is largely unknown. Therefore, this study continues to seek an efficient treatment option for metal sulfide scale management. Static bottle tests and dynamic scale loop tests under anoxic conditions were conducted to understand the efficacy of the novel polymeric chemistry towards metal sulfide scaling control. To mimic various field conditions; individual metal sulfide (FeS, ZnS and PbS) as well as mixed scaling scenarios were simulated. Various coagulant and oxidant chemistries were tested to understand the impact of the upstream treatment on safe disposal of FeS nanoparticles at surface facilities. This novel polymeric chemistry was found to be not only effective towards FeS scaling control, but also towards dispersion of ZnS and PbS as well. The primary mechanism of metal sulfide scale deposition control is identified to be crystal growth inhibition and crystal surface modification. Laboratory test results indicated no negative impact of new chemistry on the performance of other chemicals (coagulant, oxidizer etc.). In fact, an enhanced efficiency of iron sulfide oxidation was observed possibly due to the large surface area of finely dispersed particles. A field throughput study results indicated superior performance compared to that of various incumbent chemistries. Based on the laboratory results, it is anticipated that this chemistry will provide a new treatment option for metal sulfide scaling/deposition control. Additionally, the new chemistry did not leave any negative footprint for safe disposal of metal sulfide particulate at surface. As opposed to the calcite/barite scale, nucleation inhibition of metal sulfide may not be desired as the dissolved sulfide may cause further corrosion/deposition downstream. Therefore, the value this paper brings to the management of metal sulfides is a systematic testing and evaluation approach which confirms dispersion rather than nucleation inhibition is effective control mechanism.