Flow assurance problems in the geo-energy industry: microbial influenced corrosion, and precipitation of clays in reservoir acid stimulation

Makungu Marco Madirisha*

*Corresponding author for this work

Research output: ThesisPhD Thesis - Research UT, graduation UT

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Abstract

In the geo-energy industry, bio-corrosion of wells and surface installation, and precipitation of clays in reservoirs during acid stimulation cause several problems such as reduction of mechanical properties of the casing and pipe materials and flow path blockages. These types of problems are commonly denoted as “flow assurance problems”. The dominant factors in bio-corrosion are hard to determine because normally several species of micro-organisms and their metabolites are involved and interact. Moreover, different metabolites may cause opposing effects. The role of individual metabolites can be determined only if the influence of one metabolite is isolated from the influence of other metabolites. Moreover, the knowledge on the interaction between clays and the agents used in acid stimulation in a reservoir such as biodegradable chelating agents is paramount to avoid problems such as precipitation of clay minerals that can hamper the smooth flow of fluids and gases from the reservoir. Proper knowledge of these processes and mechanisms is a priory requirement for optimal production and avoiding flow assurance problems.
The purpose of this research is to improve understanding of bio-corrosion and understanding of precipitation of clay during acid stimulation as these both hamper flow assurance problems in the geo-energy industry. This research is formulated in the following research questions:

i. What is the role of biofilm in corrosion due to Sulfate Reducing Bacteria (SRB)?
ii. What is the role of organic acid metabolites in SRB corrosion?
iii. What is the influence of biodegradable chelating agents in the precipitation of clay minerals responsible for decreasing reservoir permeability?

The methodology for answering the research questions is as follows. To better understand the role of simulated biofilm and organic acid metabolites (acetic or L-ascorbic acid) in SRB corrosion, the research investigated the influence of temperature (30, 45, and 60 C) and exposure time (60 and 120 min) in the presence of simulated H2S, depleted O2 environment (CO2), brine and smooth test coupons. The influence is determined by electrochemical (PDP and EIS) and pH measurements, the chemical composition of the surface material of the test coupons using XRD and SEM-EDS, and quantities of dissolved metal ions in solution using ICP-OES. To better understand the influence of biodegradable chelating agents (BCA1, BCA2, and BCA3) in the precipitation of clays (kaolinite-natural (KN) and montmorillonite-K10 (MM)), the research investigated the influence of functional groups of biodegradable chelating agents and brine (pH, salinity and conductivity) in a depleted O2 environment with constant temperature and pressure. The influence is determined by changes in surface properties of the clay minerals using porosimetry, ATR-FTIR, XRD, and infrared reflectance spectroscopy, and quantities of dissolved metal ions in solution using ICP-OES. Reference experiments are done for all investigations. Furthermore, multiple linear regression and t-tests are used to analyze the data obtained.
The results show that the simulated biofilm in the reference experiments at 60 min exposure time has a very small inhibiting effect on corrosion while at 120 min exposure time and in brine experiments neither inhibits nor accelerates corrosion. Furthermore, the obtained corrosion rates (0.25 to 1.6 mm/year) in a simulated SRB environment are comparable to published corrosion rates obtained in SRB experiments (0.20 to 1.2 mm/year). Results on the role of organic acid metabolites show that simulated organic acid metabolites accelerate corrosion in a simulated SRB environment. However, a comparison of these results with those for a simulated SRB environment without acetic or L-ascorbic acid under similar experimental conditions shows that the addition of acetic results in an inhibitory effect while the addition of L-ascorbic acid results in acceleration of corrosion. The results to understand the influence of biodegradable chelating agents show changes in surface properties and structure of KN and MM which in turn suggest chemical interaction to take place. The ICP-OES, pH, conductivity, and salinity results strongly support that chemical interactions (dissolution reactions) take place. BCAs’ functional groups have more influence than pH on the dissolution. BCA1 and BCA3 cause greater dissolution with lower precipitation as compared to BCA2 and no-BCA.
The results on the role of biofilm contradict the existing literature. This discrepancy is likely due to differences in experimental conditions as the majority of MIC literature and laboratory investigations are focused on H2S as the only SRB product. Such studies ignore the presence of metabolic heterogeneity in SRB and the presence of biofilm and CO2 that are likely to have their kinetics/influence on corrosion. Despite the discrepancy in the role of biofilm in SRB simulated studies, the obtained corrosion rates in a simulated SRB environment in this study are comparable to published corrosion rates obtained in SRB experiments implying that simulated H2S, CO2, and biofilm are representative of the SRB media for corrosion studies. Moreover, the results on the role of simulated organic acid metabolites highlight that H2S has the key role in corrosion in the presence of acetic or L-ascorbic acid. The results are important new and novel information on the role of acetic and L-ascorbic acids in corrosion of geo-energy pipelines in the SRB environment. The results have a direct impact on the role of other microbial metabolites in the corrosion of carbon steel. In acid stimulation using BCAs, the results reveal that BCA1 and BCA3 could be useful acids for reservoir stimulation for improving permeability, especially in geothermal reservoir formations that contain clay minerals.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Faculty of Geo-Information Science and Earth Observation
  • University of Twente
Supervisors/Advisors
  • van der Meer, Freek, Supervisor
  • Hack, R., Supervisor
Award date22 Jun 2022
Place of PublicationEnschede
Publisher
Print ISBNs978-90-365-5398-8
DOIs
Publication statusPublished - 22 Jun 2022

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