Oil and gas production field requirements to maintain asset integrity and scale control are very diverse. In an operator’s field in Latin America, the conditions across several wells required the co-injection of corrosion and scale inhibitors. The brine composition of these wells is challenging due to relatively high concentration of calcium ions as well as the presence of iron. The selected scale and corrosion inhibitors need to be compatible with brine and with each other without negatively impacting the absolute performance of the individual products. An additional practical challenge for product selection was imposed by the extreme remote location of the field requiring the product to perform at an optimal dosage without increased transportation and logistics costs.
This paper describes the results from screening studies conducted with a series of corrosion inhibitor product formulations using different static and dynamic lab performance evaluation test methods. As the primary corrosion inhibitor actives are oil-soluble by nature, focus was given to formulating the product with an appropriate selection of solvents, such as methanol and isopropanol, and surfactants to achieve the desired compatibility with the brine and scale inhibitors. The final products were identified, and an optimal product dosage was arrived at based on tests conducted under typical and aggressive conditions representative of the field. However, due to the diversity of conditions and corrosion severity levels across multiple wells in this field, corrosion prediction simulations were run for unmonitored wells to estimate a baseline corrosion rate and build confidence in the recommended corrosion inhibitor product dosage. The validation of the prediction for monitored wells with ER probes will also be discussed in this study.
Laboratory testing of corrosion inhibitors under high temperature high pressure (HTHP) conditions is challenging. HTHP testing has been traditionally performed in closed systems with fixed liquid/gas volume and testing results are usually influenced/compromised by the accumulation of ferrous ions and corrosion products. The aim of the work is to optimize corrosion inhibitor testing conditions at HTHP to generate results of better reliability. The corrosion of carbon steel by CO2 at HTHP was assessed using small working electrodes of large liquid volume-to-sample surface area in autoclaves. The effect of CO2 partial pressure was also investigated. The blank and inhibited corrosion rates were monitored by linear polarization resistance (LPR) and the morphology of coupon surface was measured by vertical scanning interferometry (VSI). The testing results were deemed to be more representative of the field service environment when the amount of ferrous ions and corrosion products was reduced due to the usage of small working electrodes.
Accurate and precise monitoring of corrosion inhibitors in oilfield brine, an important aspect of corrosion control in oil and gas operations, is also a practice recommended by NACE International guidelines. Many operators require residual concentrations of corrosion inhibitors to monitor chemical deliverability at specific locations in a production system. The residual measurement provides the ability to troubleshoot factors affecting chemical deliverability. However, residual measurements are notoriously problematic because of the surface-active nature of corrosion inhibitors. Residual measurement errors can often exceed 100 percent. Consequently, a need exists for methods that are precise and accurately detect a wider range of corrosion inhibitor molecules. These methods must also be viable in corrosive oilfield environments where corrosion inhibitors are at low concentrations. Furthermore, the methods must be portable, enabling field analysis of residual chemicals in collected samples. Field-based detection methods can reduce the amount of time required to obtain data useful for corrosion control and reduce delays associated in shipping samples to centralized laboratories.