Corrosion inhibitors are widely used to guarantee asset integrity from oil exploration and production stages (e.g. drilling equipment and metal piping in producing wells) to refinery, as well as during transportation of produced fluids and finished by-products. The major forms of corrosion found among the oil and gas industry include chemical, electrochemical, mechanical, and microbiologically induced. Corrosion inhibition by organic compounds is applied mostly in electrochemical corrosion due to acidic gases (H2S and CO2), from which CO2 corrosion is considered one of the major threats in oil and gas producing assets. According to the literature, amide and amine/diamine are the main classes of corrosion inhibitors used to combat sweet corrosion (CO2) in oilfields. However, the constant need to overcome new challenges makes it possible to create novel chemicals or to identify well-known molecules that can be improved in order to meet both the market demands and technical requirements, for example: guaranteed inhibitory capacity under several conditions, low emulsion and foaming tendency. In the present work, evaluations of different alkoxylation degrees and types of diamines were carried out in order to analyze the influence on the corrosion behavior of a carbon steel surface (SAE 1020 and API 5L X65), as well as emulsion and foaming tendencies. For these studies, the corrosion measurements were either performed by linear polarization resistance (LPR) or by weight loss measurements. The data revealed that their corrosion protection of carbon steel depended critically on the alkoxylation type and degree. Therefore, a suitable choice of molecule can create a tailor-made product to achieve specific requirements. The chemicals developed have shown good corrosion inhibiton performance and have satisfied defined pratical requirements to avoid emulsion and foaming tendencies.
Viscoelastic surfactants (VES) have been introduced as acid divergent agents for easier cleaning and mixing advantage over in-situ gelled acid systems. Thermal stability and compatibility with the other additives, such as corrosion inhibitors, are the main problems with conventional VES. This work introduces five VES-based acid systems for diversion in matrix acidizing. A series of VES samples were developed, hereinafter named samples A, A1, B, C and C1 according to their chemical composition, and evaluated for various applications. The initial screening was conducted by viscosity measurements of the spent acid system at 150°F and shear rates of 10 and 100 s−1. The effects of different corrosion inhibitors on the viscosity of the selected VES were then examined. The viscosity of the VES system was then measured as a function of temperature (77 to 300°F) and shear rate (10 and 100 s−1) to evaluate thermal stability. The diversion characteristic of the VES systems was evaluated with single core flood experiments on Indiana limestone cores with a permeability range of 10-200 md. CT-scan imaging of the cores after the acid treatment was used to evaluate the structure and the propagation of the wormhole. Dual coreflood experiments were conducted on Indiana limestone cores with permeability contrast of 1.5-50 to examine the ability of the VES to divert the acid system on heterogeneous limestone formations. Phase separation was observed during the preparation of the systems with a samples C and C1 VES samples. High viscosity was found in the case of A and B VES systems with the viscosity of 2,500, and 350 cP at 10 and 100 s−1, respectively, at 150°F. The viscosity of the Sample A1 and B VES systems were not affected by the tested corrosion inhibitor. The single coreflood experiments revealed the ability of the VES to divert the acid system. The breakthrough injected acid volumes were 0.7 and 0.6 in the case of Sample A1 and Sample B, respectively. The wormhole tortuosity was 1.8 in sample A, compared to 1.4 in Sample B. This work introduces VES systems with superior divergent ability and viscosity measurements at high temperature even when in contact with the other acid additives, which leads to less acid spending and better wormhole structure.
During completion and workover operations, water-based, oil-based and acid-based fluids are injected into the well, entering formation pores and reaching oil reserves. Depending on the flow intensity and ambient conditions, these fluids may interact with oil to form viscous emulsions, causing several problems in the reservoir and ultimately a decline in oil production. Non-emulsifiers, when added to brines and acid solutions, are supposed to act as a barrier on the interface between the oil and the fluid, preventing emulsion formation and helping to maintain fluid’s properties and preserving the oil in the reservoir. Lately, Brazilian fields have faced challenges that resulted into the use of different fluids and brines and also different types of oil to be dealt with. Thus, the purpose of this work was to adapt some of techniques of emulsion breakage to develop novel non-emulsifiers formulations that cope with current technical and environmental requirements regarding emulsion prevention for oil exploration in Brazil. A series of studies has been conducted in order to better understand the effect of different parameters on the emulsion prevention of brines during completion operations. A Design of Experiments approach has been prepared in order to test different formulations (varying solvent and co-surfactant natures and content) in different scenarios: brines with different salts and oils with different °API. Once evaluated through adapted bottle tests, aqueous toxicity of most promising formulations has been evaluated. It has been found that solvent and surfactant types and concentrations have great effect on emulsion prevention. All those parameters were taken into account and enabled the design of an optimized formulation for the application. Further, another Design of Experiments approach has been prepared in order to understand how different scenarios impact on emulsion prevention: the novel formulation was tested against brines with different salts and oils with different °API. The effect of parameters such as oil density, BSW, brine pH, brine type and agitation could be assessed and a mechanism of action for the high performance non-emulsifier could be investigated.
In this study, a novel surfactant for flowback aid application was developed based on an optimization of well-known non-ionic surfactants. The objective was to meet intrinsic surfactant properties, such as high cloud point (CP), low surface tension (ST), adequate contact angle (CA) and low critical micelle concentration (CMC). In addition to the essential physical-chemical properties, improvement in fluid recovery and emulsion compatibility were also targeted. The surfactants were optimized by tailoring the hydrophilic head through controlled introduction of ethylene oxide and propylene oxide into different hydrophobic chains. Surface tension measurements were made with a Dataphysics Instruments model OCA-15. Contact angles were measured using the sessile-drop method. The CMC concentration and cloud point were also conducted for physical chemical characterization. For the fluid recovery evaluation, flowback solutions were poured through 150g of 60/150 mesh- dry porous media contained in a 7 cm-inner-diameter, 9.5- cm-long column. Emulsion compatibility tests were also carried out using different proportions of crude oil and brine. This paper evaluates various flowback additives in hydraulic fracturing applications between linear and branched alkoxylated surfactants. High cloud point enables a wide range of temperature applications and an increase in EO content showed an increase in cloud point values, contrary to PO effect. Nevertheless, CMC measurements showed that for an optimum scenario, EO addition should not be high, because undesired increases in CMC values may occur, which will affect the final surfactant dosage needed. All flowback aids demonstrated low surface tension as expected (approximately below 32 mN/m), but each being different in terms of surface wettability (contact angle), which could not be correlated with surfactant structure. Fluid recovery and kinetics of emulsion breakage increased significantly with different alkoxylation adjustments. For the new flowback aid developed, the fluid recovery was improved when compared against standard surfactants. Additionally, significant improvement was also found during emulsion breakage evaluation in terms of superior kinetics, final breakage, and water quality. This work provided a better understanding of how EO/PO affects intrinsic surfactant properties and enabled to find a surfactant that offers several benefits in terms of fluid recovery and non-emulsification of crude oil and water.
There is an increasing demand from oil and gas industry to ensure the integrity of assets and the enviroment in the critical conditions found in presalt wells. This study evaluates new formulations of corrosion inhibitors with different types and alkoxylation degrees of nitrogen‐based inhibitors to assess corrosion behavior of carbon steel (API X65). For these studies, corrosion rates were determined through measurements of weight loss and linear polarization resistance (LPR). In the case of electrochemical measurements, experiments were carried out in a laminar flow and in a turbulent flow regime. All data were collected in the presence of CO2 and CO2/H2S mixtures. The results revealed that corrosion protection of carbon steel critically depends on the nitrogen‐based inhibitor's alkoxylation type and degree as well as the condition to which they are exposed. It was possible to notice that an ethoxylated amine whose inhibition efficiency in the presence of CO2 was about 10%, when exposed to H2S environment at the same temperature showed an efficiency of 86%. It was also observed that the inhibitor with a higher ethoxylation degree presented better efficiencies than the one with a lower degree.
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