Elsevier

Water Research

Volume 154, 1 May 2019, Pages 12-20
Water Research

Application of iron-crosslinked sodium alginate for efficient sulfide control and reduction of oilfield produced water

https://doi.org/10.1016/j.watres.2019.01.030Get rights and content

Highlights

  • SA–Fe could control sulfide and reduce oilfield produced water simultaneously.

  • Sulfide decreased by 45 ± 3.2% in gas phase and 75 ± 4.7% in aqueous solution.

  • Water viscosity increased from 0.9 mPas to 342 mPas.

  • Produced water decreased from 70.1 ± 4.0 to 37.5 ± 1.3 mL water/mL oil.

  • The theoretical FeS was nearly equal to the actual generated FeS.

Abstract

Sulfide production and oilfield produced water are considered as environmental challenges in the oil industry. Iron-crosslinked sodium alginate (SA–Fe) was used to address these problems simultaneously. A pair of columns containing one coarse-sand column and one fine-sand column was designed to simulate heterogeneous rock layers and evaluate the plugging effect of SA–Fe. Generation of FeS precipitates led to decreases of sulfide in the gas phase by 45 ± 3.2% and in the aqueous solution by 75 ± 4.7%. The generated FeS nanoparticles and sulfate-reducing bacteria attached on the surface of the sand in the coarse-sand column to plug the pores that caused the water flow to switch from the coarse-sand column to the fine-sand column. Analysis of FeS distribution indicated that the column inlet was effectively plugged by FeS. The theoretical amount of FeS (1.19 mmol) that was determined based on sulfur balance was nearly equal to the actual amount of FeS precipitation (1.11 mmol). Additionally, water viscosity increased from 0.9 mPas to 342 mPas, induced by the collapse of SA–Fe gels, which reduced the difference in viscosity between oil and water to avoid viscous fingering. As a consequence, the oil recovery improved from 46 ± 2.6% to 85 ± 3.0% in the sand column oil-saturated recovery experiment, which contributed to the decrease of oil-normalized produced water from 70.1 ± 4.0 to 37.5 ± 1.3 mL water/mL oil. Therefore, this study shows that SA–Fe exhibits potential for application in controlling sulfide as well as reducing produced water.

Introduction

Oil is likely to continue being the dominant source of energy worldwide through 2030 (Abas et al., 2015). Sulfide production in oil exploitation is a serious concern because it causes detrimental problems, such as malodors, health hazards, and corrosion (Washio et al., 2005; Beauchamp et al., 1984; Ren et al., 2005; Hessel et al., 1997), which inevitably lead to environmental issues and high costs. Sulfide is mediated by the activity of sulfate-reducing bacteria (SRB) present primarily in the reservoir (Nemati et al., 2001). Different approaches to controlling sulfide production have been proposed. SRB activity is typically inhibited by treatment of injection water with biocides (e.g., glutaraldehyde and cocodiamines) and nitrate/nitrite (Greene et al., 2006; Xue and Voordouw, 2015). The introduction of these chemicals may lead to groundwater contamination and entail high costs for the oil industry (Nas and Berktay, 2006; Lin et al., 2008; Okafor and Ogbonna, 2003).

In the wastewater treatment industry, the detriment from sulfide production also presents a problem (Carrera et al., 2016). Considerable amount of researches were conducted on sulfide control (Gutierrez et al., 2008; Ganigue et al., 2011). Addition of metallic salts has been reported to achieve sulfide precipitation by forming highly insoluble metallic sulfide precipitates, thereby decreasing the amount of sulfide available for release to the atmosphere (Zhang et al. 2008, 2009). These studies involved iron salts (e.g., Fe(III) and Fe(II)), which can effectively reduce dissolved sulfide from wastewater to form FeS precipitates (Zhang et al., 2009; Gutierrez et al., 2010). Therefore, this method provides a basis for the treatment of injection water with iron salts for oil production to control sulfide. However, the directionless penetration of injection iron solution is wasteful and results in unwanted plugging of the reservoir. Therefore, a more cost-effective and targeted method should be highly beneficial for iron addition.

For some mature oilfields, secondary recovery is the main stage that uses water flushing to enhance oil recovery, thus vast quantities of process water has been consumed and consequently vast amounts of wastewater has been generated. Produced water, a mixture of different organic and inorganic compounds, is the largest waste stream generated in oil industries and effect of discharging produced water on the environment has lately become a significant issue of environmental concern (Sheikhyousefi et al., 2017; Ahmadun et al., 2009). Produced water is conventionally treated through different chemical (Xu et al., 2008), physical (Murray-Gulde et al., 2003), and biological methods (Campos et al., 2002). For example, Weschenfelder et al. (2015) reported that microfiltration process enabled the treatment and reuse of produced water using ceramic membranes. Lu et al. (2009) conducted on a hydrolysis acidification/bio-contact oxidation system to treat oilfield produced water with high salinity. All aforementioned methods focused on the treatment of produced water. It may be an alternative method to reduce the production of produced water from the origin, which is to use less water to recover more oil. Therefore, how to enhance oil recovery is the key of reducing oilfield produced water.

In the secondary oil recovery, long-term water flooding generally causes poor sweep efficiency because of preferential flow paths (Wu et al., 2017a). These factors necessitate tertiary or enhanced oil recovery (EOR), including chemically- and microbially-assisted methods. Polymer flooding is a well-established technique for addressing the aforementioned problem, enhancing oil recovery with the application for more than 40 years (Abidin et al., 2012); however, the high cost and poor shear resistance involved in this technique have yet to be addressed. Microorganisms and extracellular polymeric substances (EPSs) (e.g., bioclogging) as effective methods to reduce permeability have been demonstrated in previous mathematical models and experiments (Ezeuko et al., 2011; Surasani et al., 2013; Thullner, 2010; Stewart and Fogler, 2001), which require necessary nutrients, leading to high costs. Meanwhile, bioclogging is not secure because of the complexity of the underground environment. Therefore, various biominerals, such as CaCO3 and Fe(OH)3, have been proposed to reduce the permeability and thus redirect the displacement fluid into previously bypassed portions of the reservoir. Our previous study that relied on CaCO3 to achieve EOR was conducted (Wu et al., 2017a). Zhu et al. (2013) used anaerobic nitrate-dependent Fe(II) oxidation to form Fe(OH)3 biominerals to plug the large-flow channel for promoting oil recovery.

In our previous study, the polysaccharide sodium alginate (SA) was used to achieve microbial self-healing for EOR (Wu et al., 2017b). SA, a biodegradable and biocompatible polysaccharide, exhibits a significantly high affinity to divalent metal ions (e.g., Ca2+, Fe2+) (Haug et al., 1967; Rees and Welsh, 1977). It is composed of a 1–4-linked block polymer of polyglucuronate, polymannuronic acids. Contact between an alginate solution and divalent cations causes gelation (Liu et al., 2012). The crosslinked divalent cation is dispersed homogeneously in the gel and wrapped by organic matrix. Once the crosslinked divalent cation is lost, the gel collapses and again forms a viscous SA solution. Given its aforementioned nature, SA can be used potentially as iron-crosslinked SA (SA–Fe) for the oil industry.

Thus, this study was aimed at using SA–Fe to control sulfide production and reduce oilfield produced water simultaneously. Three column sets were established to measure sulfide production in these column experiments and evaluate the plugging effect of SA–Fe according to the direction of the water flow. Sulfide production and water viscosity were also recorded. The column was subjected to destructive sampling to study the distribution of FeS precipitation in the coarse-sand column. In addition, a sand column oil-saturated recovery experiment was performed to evaluate the effect of SA–Fe on oil recovery and then calculate the oil-normalized produced water. This study presents a potential application of SA–Fe in reducing the pollution of sulfide and produced water in oil exploitation.

Section snippets

Microorganisms and cultivation

Desulfovibrio vulgaris (NBRC 104121), a sulfate-reducing bacterium, was purchased from the National Institute of Technology and Evaluation of Japan. It was first anaerobically cultivated in a serum bottle up to the stationary phase at 37 °C with NBRC Medium 1021, which consisted of the following: 0.5 g/L K2HPO4, 1 g/L NH4Cl, 1 g/L Na2SO4, 0.1 g/L CaCl2·2H2O, 2 g/L MgSO4·7H2O, 2 g/L sodium lactate, 1 g/L yeast extract, 1 mg/L resazurin, and 10 g/L thioglycolate solution (0.1 g sodium

Sulfide production

A previous study demonstrated that the concentrations of thiosulfate and sulfite in all reactors were not significant (<0.5 mg S/L) and that all of the sulfate reduced was converted to sulfide (Zhang et al., 2009). Accordingly, only sulfide as the reductive product of sulfate was measured. Sulfide production in the column experiments was recorded. The concentration of hydrogen sulfide in the gas phase is shown in Fig. 2A. When Fe(II) was not added to the medium (i.e., Column Set 3), the

Conclusions

In this study, SA–Fe was used to control sulfide and reduce produced water that are considered as environmental challenges in the oil industry. The main outcomes were:

  • Generation of FeS precipitates led to decreases of sulfide in the gas phase by 45 ± 3.2% and in the aqueous solution by 75 ± 4.7%.

  • The generated FeS nanoparticles and sulfate-reducing bacteria attached on the surface of the sand in the coarse-sand column to plug the pores that caused the water flow to switch from the coarse-sand

Declaration of interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors would like to acknowledge the financial support of the National Science Foundation of China (51878175) and the Program for Innovative Research Team in Science and Technology in Fujian Province University (IRTSTFJ).

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