PhD Defence by Maksim Kurbasov
This PhD project investigates formation damage during produced water reinjection (PWRI) in mature chalk reservoirs, with a focus on the Danish North Sea. By combining core flooding experiments with microfluidic techniques, the research explores how inorganic scaling, organic deposition, and microbial activity interact to reduce permeability near the wellbore.
This dissertation presents an investigation into the mechanisms of near-wellbore formation damage that occurs during produced water reinjection, using a combination of advanced microfluidic techniques and core flooding experiments.
The problem of injectivity decline, especially in mature oil fields such as those found in the Danish sector of the North Sea, remains a critical challenge for the oil and gas industry. This study focuses on how a variety of factors, including inorganic scaling, organic matter deposition, and microbial activity, impact the permeability of chalk formations.
A key aspect of this research is its novel multi-phase experimental approach, which integrates microfluidic technologies for in-situ fluid monitoring at the microscale with conventional core flooding tests to capture larger-scale permeability shifts. By bridging these two experimental domains, the study provides new insights into how these damaging processes interact and influence injectivity during produced water reinjection.
One of the central innovations of this research lies in its comprehensive treatment of both inorganic and organic factors that contribute to near-wellbore damage. While previous studies have often focused on these elements in isolation, this work uniquely examines their combined effects. The microfluidic experiments enabled real-time observation of fluid flow and pore-clogging phenomena at the microscopic level, while core flooding tests offered valuable macroscopic data on permeability alterations. The integration of these two methodologies provided a holistic view of the damage mechanisms, revealing the critical interplay between scaling, bacterial biofilms, and organic deposition, which are often the primary drivers of injectivity decline in chalk formations.
These findings have broad implications for oil field management, particularly in optimizing water injection processes and improving well productivity. The core flooding experiments in this study were carried out using chalk core samples from the Dan field in the North Sea. The experiments primarily focused on evaluating permeability reduction when injecting different seawater mixtures and produced water. One significant finding from these experiments was the rapid decrease in permeability when 80% seawater and 20% produced water were injected into the chalk cores. Permeability was found to drop by 94% after the injection of 295 pore volumes. This result was corroborated by extensive scanning electron microscopy and ion chromatography analyses, which identified large quantities of iron-silicon precipitates and sodium chloride salts blocking the pore channels.
Further insights were gained through the use of microfluidic experiments, which allowed for the visualization of fluid flow and bacterial activity under conditions that simulate real reservoir environments. These experiments, conducted at 70°C to mimic reservoir temperatures, involved the injection of 650 pore volumes of a produced water and seawater mixture. Unlike the core flooding experiments, the microfluidic model showed that complete pore blockage did not occur due to the larger pore diameters (approximately 50 microns in the microfluidic channels compared to the 0.5–1 micron size in real reservoir cores).
However, significant localized blockages were observed due to the proliferation of bacterial colonies, which rapidly expanded to fill smaller pore spaces. This was a critical finding, as it demonstrated the dual impact of inorganic scale and bacterial biofilms on permeability reduction. The numerical results from these experiments were highly illustrative of the mechanisms driving permeability loss. For example, in synthetic produced water experiments, permeability reduction proceeded at a slower rate compared to real produced water tests. After injecting 250 pore volumes of synthetic water, permeability decreased by 50%, whereas with real produced water, permeability reduction reached 78% after the same volume. This difference is attributed to the presence of organic compounds and bacteria in real produced water, which form films and contribute significantly to pore clogging. The results indicate that biofilm formation is particularly problematic in areas where pore sizes are small, as these films tend to expand and block fluid pathways more effectively in such regions.
Another significant finding from this dissertation is the role that critical raw material extraction could play in mitigating formation damage. The study proposes an innovative approach to using produced water not just as a waste product but as a valuable resource for extracting materials like lithium, which are crucial for the green energy transition. The experiments showed that removing ions such as iron and silicon from the produced water before reinjection can significantly reduce the risk of scaling and biofilm formation, thus preserving permeability and improving injectivity.
This dual approach of managing produced water by both optimizing its composition and extracting valuable elements represents a promising direction for the oil and gas industry, particularly in reducing the environmental footprint of offshore operations. In the core flooding experiments, real produced water samples demonstrated a rapid reduction in permeability, with a 50% reduction observed after the injection of just 200 pore volumes. By comparison, synthetic produced water, free from organic components and microbial contamination, showed a slower permeability decline, reinforcing the critical role that organic and bacterial factors play in accelerating formation damage.
The research also highlights how different reinjection strategies, such as altering the ratio of seawater to produced water or incorporating biocides and scale inhibitors, can impact permeability outcomes. For instance, injecting a 50/50 mixture of seawater and produced water resulted in an 80% reduction in permeability after 300 pore volumes, a less severe impact compared to the 94% reduction seen with a higher concentration of seawater. These insights are crucial for developing more effective water management practices, particularly in fields where produced water reinjection is necessary to maintain reservoir pressure and sustain oil production.
One of the most novel aspects of this dissertation is its investigation into how microbial growth can be controlled to minimize its detrimental impact on reservoir permeability. The study extensively discusses the role of sulfate-reducing bacteria, which were found to thrive in environments where oxygen scavengers were not adequately used, leading to the formation of dense biofilms that blocked pores and reduced permeability. The use of microfluidic devices enabled the real-time monitoring of these biofilms, revealing that even small colonies of bacteria can have a disproportionate effect on fluid flow in reservoirs with low-permeability formations such as chalk.
The results suggest that implementing more rigorous biocide treatments or altering injection water chemistry could be effective in mitigating the impact of microbial activity on injectivity. The broader implications of this research are significant for both the oil and gas industry and environmental sustainability. The findings presented in this dissertation underscore the need for better produced water treatment technologies, which not only mitigate the risk of formation damage but also allow for the extraction of valuable materials, contributing to more sustainable energy practices. By identifying the combined effects of inorganic scaling and microbial biofilms, this work provides a framework for developing more targeted interventions to prevent permeability loss during produced water reinjection.
Moreover, the proposed methods for critical raw material extraction from produced water open new opportunities for reducing the environmental impact of offshore oil production, particularly in ecologically sensitive regions such as the North Sea.
In conclusion, this dissertation provides significant insights for the understanding of near-wellbore formation damage during produced water reinjection. The integration of core flooding experiments with advanced microfluidic techniques has enabled a detailed investigation into the mechanisms behind injectivity loss, providing both macroscopic and microscopic perspectives. The research has highlighted the critical role of inorganic scale formation, bacterial biofilms, and organic matter in reducing permeability, and has proposed practical solutions for mitigating these effects through improved water treatment and the extraction of critical raw materials. These findings have important implications for optimizing waterflooding strategies, enhancing oil recovery, and minimizing the environmental impact of oil production operations.
The problem of injectivity decline, especially in mature oil fields such as those found in the Danish sector of the North Sea, remains a critical challenge for the oil and gas industry. This study focuses on how a variety of factors, including inorganic scaling, organic matter deposition, and microbial activity, impact the permeability of chalk formations.
A key aspect of this research is its novel multi-phase experimental approach, which integrates microfluidic technologies for in-situ fluid monitoring at the microscale with conventional core flooding tests to capture larger-scale permeability shifts. By bridging these two experimental domains, the study provides new insights into how these damaging processes interact and influence injectivity during produced water reinjection.
One of the central innovations of this research lies in its comprehensive treatment of both inorganic and organic factors that contribute to near-wellbore damage. While previous studies have often focused on these elements in isolation, this work uniquely examines their combined effects. The microfluidic experiments enabled real-time observation of fluid flow and pore-clogging phenomena at the microscopic level, while core flooding tests offered valuable macroscopic data on permeability alterations. The integration of these two methodologies provided a holistic view of the damage mechanisms, revealing the critical interplay between scaling, bacterial biofilms, and organic deposition, which are often the primary drivers of injectivity decline in chalk formations.
These findings have broad implications for oil field management, particularly in optimizing water injection processes and improving well productivity. The core flooding experiments in this study were carried out using chalk core samples from the Dan field in the North Sea. The experiments primarily focused on evaluating permeability reduction when injecting different seawater mixtures and produced water. One significant finding from these experiments was the rapid decrease in permeability when 80% seawater and 20% produced water were injected into the chalk cores. Permeability was found to drop by 94% after the injection of 295 pore volumes. This result was corroborated by extensive scanning electron microscopy and ion chromatography analyses, which identified large quantities of iron-silicon precipitates and sodium chloride salts blocking the pore channels.
Further insights were gained through the use of microfluidic experiments, which allowed for the visualization of fluid flow and bacterial activity under conditions that simulate real reservoir environments. These experiments, conducted at 70°C to mimic reservoir temperatures, involved the injection of 650 pore volumes of a produced water and seawater mixture. Unlike the core flooding experiments, the microfluidic model showed that complete pore blockage did not occur due to the larger pore diameters (approximately 50 microns in the microfluidic channels compared to the 0.5–1 micron size in real reservoir cores).
However, significant localized blockages were observed due to the proliferation of bacterial colonies, which rapidly expanded to fill smaller pore spaces. This was a critical finding, as it demonstrated the dual impact of inorganic scale and bacterial biofilms on permeability reduction. The numerical results from these experiments were highly illustrative of the mechanisms driving permeability loss. For example, in synthetic produced water experiments, permeability reduction proceeded at a slower rate compared to real produced water tests. After injecting 250 pore volumes of synthetic water, permeability decreased by 50%, whereas with real produced water, permeability reduction reached 78% after the same volume. This difference is attributed to the presence of organic compounds and bacteria in real produced water, which form films and contribute significantly to pore clogging. The results indicate that biofilm formation is particularly problematic in areas where pore sizes are small, as these films tend to expand and block fluid pathways more effectively in such regions.
Another significant finding from this dissertation is the role that critical raw material extraction could play in mitigating formation damage. The study proposes an innovative approach to using produced water not just as a waste product but as a valuable resource for extracting materials like lithium, which are crucial for the green energy transition. The experiments showed that removing ions such as iron and silicon from the produced water before reinjection can significantly reduce the risk of scaling and biofilm formation, thus preserving permeability and improving injectivity.
This dual approach of managing produced water by both optimizing its composition and extracting valuable elements represents a promising direction for the oil and gas industry, particularly in reducing the environmental footprint of offshore operations. In the core flooding experiments, real produced water samples demonstrated a rapid reduction in permeability, with a 50% reduction observed after the injection of just 200 pore volumes. By comparison, synthetic produced water, free from organic components and microbial contamination, showed a slower permeability decline, reinforcing the critical role that organic and bacterial factors play in accelerating formation damage.
The research also highlights how different reinjection strategies, such as altering the ratio of seawater to produced water or incorporating biocides and scale inhibitors, can impact permeability outcomes. For instance, injecting a 50/50 mixture of seawater and produced water resulted in an 80% reduction in permeability after 300 pore volumes, a less severe impact compared to the 94% reduction seen with a higher concentration of seawater. These insights are crucial for developing more effective water management practices, particularly in fields where produced water reinjection is necessary to maintain reservoir pressure and sustain oil production.
One of the most novel aspects of this dissertation is its investigation into how microbial growth can be controlled to minimize its detrimental impact on reservoir permeability. The study extensively discusses the role of sulfate-reducing bacteria, which were found to thrive in environments where oxygen scavengers were not adequately used, leading to the formation of dense biofilms that blocked pores and reduced permeability. The use of microfluidic devices enabled the real-time monitoring of these biofilms, revealing that even small colonies of bacteria can have a disproportionate effect on fluid flow in reservoirs with low-permeability formations such as chalk.
The results suggest that implementing more rigorous biocide treatments or altering injection water chemistry could be effective in mitigating the impact of microbial activity on injectivity. The broader implications of this research are significant for both the oil and gas industry and environmental sustainability. The findings presented in this dissertation underscore the need for better produced water treatment technologies, which not only mitigate the risk of formation damage but also allow for the extraction of valuable materials, contributing to more sustainable energy practices. By identifying the combined effects of inorganic scaling and microbial biofilms, this work provides a framework for developing more targeted interventions to prevent permeability loss during produced water reinjection.
Moreover, the proposed methods for critical raw material extraction from produced water open new opportunities for reducing the environmental impact of offshore oil production, particularly in ecologically sensitive regions such as the North Sea.
In conclusion, this dissertation provides significant insights for the understanding of near-wellbore formation damage during produced water reinjection. The integration of core flooding experiments with advanced microfluidic techniques has enabled a detailed investigation into the mechanisms behind injectivity loss, providing both macroscopic and microscopic perspectives. The research has highlighted the critical role of inorganic scale formation, bacterial biofilms, and organic matter in reducing permeability, and has proposed practical solutions for mitigating these effects through improved water treatment and the extraction of critical raw materials. These findings have important implications for optimizing waterflooding strategies, enhancing oil recovery, and minimizing the environmental impact of oil production operations.