Experimental and analytical investigation of an immiscible displacement process in real structure micromodels

The recovery of oil from a reservoir can be accomplished with various methods, one of the most commonly applied types being waterflooding. A common theory used to describe immiscible displacement is the Buckley–Leverett theory. A brand new type of micromodel, generated and fabricated by using a micro-computer tomography (μCT) image stack of a real sandstone core, was used to conduct immiscible displacement experiments. Critical logging data were recorded, and a high-resolution camera took pictures of the displacement process. In an image processing tool (MATLAB), an algorithm was developed to evaluate the pictures of the experiment and to examine the changes in the saturations of the displacing and the displaced fluid. The main objective of the displacement experiment was to validate the new microchip in two-phase displacement experiments and to assess the feasibility of the image processing algorithm. This was performed by comparing the results of the experimental to the analytical solutions, which were derived from the Buckley–Leverett theory. The comparison of the results showed a good match between the two types of solutions. The applicability of the analytical results to the experimental procedures was observed. Additionally, the usage of the newly fabricated micromodel and its potential to visualize the fluid flow behavior in porous media were assessed

Integrated Analysis of Optimizing Tubing Material Selection for Gas Wells

Corrosion in production tubing strings is seen as a challenging problem in gas wells containing carbon dioxideand hydrogen sulfide. This paper presents a new comprehensive method of corrosion rate calculation with integrated study of reservoir condition, nodal analysis of the well, and well trajectory, which could also have an effect due to the possibility of different flow regimes of the production fluid. This method  is applicable to evaluate and predict the performance of selected tubing size and material. This method can also give an economic evaluation for the consideration of using corrosion resistant alloy (CRA) or low-alloy steel and carbon steel. The measurement of corrosion rate can be done by several methods,such as using corrosion coupons, calculating the iron content inside  the production fluid, or probes. Either way, when  the corrosion rate measured in the field is still below the acceptable maximum corrosion rate, it can be said that the adequacy of this method is guaranteed. This method has been implemented in a gas field,where it successfully selected the best tubing material for the next development well in this field. Consequently, the lifetime of the tubing strings could be extended,resulting in an economical benefit as well

Experimental and numerical investigation of pore-scale mechanisms of microbial enhanced oil recovery (MEOR) using a microfluidics approach

The utilization of microorganisms as an enhanced oil recovery (EOR) method has attracted much attention in recent years because it is a low-cost, easy to apply and environmentally friendly technology. However, the pore-scale mechanisms involved in microbial enhanced oil recovery (MEOR) that contribute to an additional oil recovery are not fully understood so far. This work aims to investigate the MEOR mechanisms using microfluidic technology, among others, bioplugging and changes in fluid viscosity as well as wettability alteration. Further, the contribution of these mechanisms to additional oil recovery was quantified. A novel experimental setup that enables investigation of MEOR in micromodels under elevated pressure, reservoir temperature and anaerobic and sterile conditions was developed. Micromodels designed based on real rocks structures were constructed with two different permeability zones for the investigation of bioplugging effects and conformance improvement during the MEOR process. An image processing algorithm was developed to estimate the bacteria growth and transport as well as fluid phase saturation in micromodels. To investigate the role of microorganisms in MEOR processes, the single and two-phase experiments were performed with fluids from a German high-salinity oil field selected for a potential MEOR application. Several parameters that govern the MEOR performance were investigated, including (1) bacteria growth, which is controlled by the nutrient concentration and incubation conditions as well as the flooding operation management, (2) bacteria community, (3) properties of porous media such as pore size and wettability. Furthermore, a numerical approach was applied to understand the significance of contributing mechanisms to oil displacement efficiency. As a result, in-situ bacteria growth was observed in the micromodel for both single and two-phase flooding experiments. During the injection, microbial cells were partly transported through the micromodel but also remained attached to the micromodel surface. These attached bacteria and biofilm formation cause the permeability reduction in micromodels and possibly the wettability alteration. Two-phase flow experiments in a customized heterogeneous micromodel showed a significant effect of bioplugging and improved the macroscopic conformance of the oil displacement process. The increase in differential pressure after bacteria incubation and microscopic visualization confirmed bioplugging in micromodels. The flow diversion of the tracer particles and the differences in the velocity field also confirmed that bioplugging might lead to improved conformance control. Additionally, during the metabolism, microorganisms were observed produced gas that could dissolve in the liquid phase, thus reducing the viscosity. This oil viscosity reduction was identified to contribute to incremental oil in micromodel experiments. The simulation results showed that the bacteria growth and transport in micromodels could be reproduced through the chemical reactions and the kinetic model. Furthermore, several oil displacement mechanisms during MEOR were evaluated in the simulation model, including bioplugging effect due to the attachment of bacterial cells, oil viscosity reduction due to the dissolution of CO2, and relative permeability change due to bacteria adsorption and biofilms onto the surface of the rock. Based on the simulation result, it can be concluded that these three mechanisms contribute to oil displacement efficiency during the MEOR process in micromodels.Die Nutzung von Mikroorganismen als Methode für die tertiäre Erdölgewinnung erhielt in den letzten Jahren viel Aufmerksamkeit, da es eine kostengünstige, leicht anwendbare und umweltfreundliche Technologie dartellen könnte. Dennoch existiert kein vollständiges Verständnis über die Porenskalamechanismen, die bei der “microbial enhanced oil recovery (MEOR)” für die zusätzliche Erdölgewinnung verantwortlich sind. Die vorliegende Arbeit zielt darauf ab die MEOR-Mechanismen mit Hilfe von Mikrofluidiktechnologien zu untersuchen, u.a. sind dies Biokolmation, Änderungen der Fluidviskosität und Veränderungen der Oberflächenbenetzbarkeit. Weiterhin wurde der Beitrag dieser Mechanismen zur zusätzlichen Erdölgewinnung quantifiziert. Ein neuartiger experimenteller Aufbau, der es erlaubt MEOR in Mikromodellen unter angehobenem Druck, Lagerstättentemperatur sowie sauerstofffreien und sterilen Bedingungen zu untersuchen, wurde entwickelt. Basierend auf realen Gesteinsstrukturen wurden Mikromodelle mit zwei verschiedenen Permeabilitätszonen gestaltet und für die Untersuchung des Biokolmationseffekts und der Konformitätsverbesserung während des MEOR-Prozesses hergestellt. Ein Bilddatenverarbeitungsalgorithmus wurde für die Abschätzung des Wachstums und Transports von Bakterien, sowie für die Fluidphasensättigung in den Mikromodellen entwickelt. Um die Rolle der Mikroorganismen in MEOR-Prozessen zu untersuchen, wurden Einphasen- und Zweiphasenexperimente mit Fluiden aus einem deutschen hoch salinen Ölfeld, das für eine potentielle MEOR-Anwendung ausgewählt wurde, durchgeführt. Verschiedene Parameter, die die Leistungsfähigkeit der MEOR-Methode steuern, wurden untersucht: (1) Bakterielles Wachstum, welches von der Nährstoffkonzentration und den Inkubationsbedingungen, sowie von der Flutbetriebsdurchführung beeinflusst wird, (2) Bakteriengemeinschaft, (3) Eigenschaften des porösen Mediums wie z.B. Porengröße und Benetzbarkeit. Zusätzlich wurde ein numerischer Ansatz angewendet, um die Bedeutung der beitragenden Mechanismen zur Effizienz der Ölverdrängung zu verstehen. Die Ergebnisse zeigen, dass bakterielles Wachstum bei Einphasen- und Zweiphasenexperimenten im Mikromodell beobachtet werden kann. Während der Injektion wurden die bakteriellen Zellen teilweise durch das Mikromodell transportiert aber blieben zum Teil auch an der Oberfläche des Mikromodells angehaftet. Diese angehafteten Bakterien und ihre Biofilmbildung sorgen für eine Reduktion der Permeabilität des Mikromodells und möglichweise für die Veränderung der Oberflächenbenetzbarkeit. Zweiphasenströmungsexperimente in einem angepassten heterogenen Mikromodell zeigten einen signifikanten Einfluss der Biokolmation und dadurch eine verbesserte Konformität des Ölverdrängungsprozesses. Der Anstieg des Differenzdrucks nach der Bakterieninkubation und die mikroskopische Visualisierung bestätigen die Biokolmation im Mikromodell. Die Strömungsumlenkung von Tracerpartikeln und der Unterschied im Geschwindigkeitsfeld bestätigen, dass Biokolmation zu einer verbesserten Konformitätskontrolle führt. Zusätzlich wurde während des Stoffwechsels beobachtet, dass die Mikroorganismen Gas produzieren, welches sich in der flüssigen Phase einlösen könnte und dadurch die Viskosität reduziert. Diese Reduzierung der Ölviskosität ist als Beitrag zur zusätzlichen Ölgewinnung identifiziert worden. Die Simulationsergebnisse zeigten, dass das Wachstum und der Transport von Bakterien in den Mikromodellen durch chemische Reaktionen und ein kinetisches Modell reproduziert werden kann. Außerdem wurden verschiedene Ölverdrängungsmechanismen, die bei der MEOR-Methode eine Rolle spielen, bewertet: Biokolmation durch die Anhaftung von mikrobiellen Zellen, Reduktion der Ölviskosität durch die Einlösung von CO2, Veränderung der relativen Permeabilität durch die Adsorption von Bakterien und Bildung von Biofilmen an den Porenwänden. Basierend auf den Simulationsergebnissen kann zurückgeschlossen werden, dass diese drei Mechanismen zur Effizient des MEOR-Prozesses in Mikromodellen beitragen

Real structure micromodels based on reservoir rocks for enhanced oil recovery (EOR) applications

Although the application of microfluidics is not new in the petroleum industry, the upscaling of fluid flow behavior from micromodels to reservoir rocks is still challenging. In this work, an attempt to close the gaps between micromodels and reservoir rocks was performed by constructing micromodels based on the X-ray micro-computed tomography (μCT) images of a Bentheimer core plug. The goal of this work was to build a digital 3D model of reservoir rocks and transfer its rock properties and morphological features such as porosity, permeability, pore and grain size distribution into a 2D microfluidics chip. The workflow consists of several steps which are (1) rock property extraction from aμCT image stack of the core plug, (2) micromodel pore structure design, (3) lithographic mask construction and (4) fabrication. Flooding experiments, including single- and two-phase flow experiments, were performed to confirm the micromodel design. As a result, the real structure micromodels show similar rock properties, as well as a comparable fluid flow behavior, to those of the Bentheimer core plug during typical water flooding and EOR polymer application. This framework demonstrates the potential for the general applicability of micromodels to support EOR studies on a larger scale, such as those on sandpacks or core plugs before field implementation

Investigation of clogging in porous media induced by microorganisms using a microfluidic application

The presence of microorganisms could alter the porous medium permeability, which is vital for several applications, including aquifer storage and recovery (ASR), enhanced oil recovery (EOR) and underground hydrogen storage. The objective of this work was to investigate the effect of bacteria and their metabolism products on clogging using micromodels under elevated pressure and temperature and anaerobic conditions. Novel micromodels (real-structure) were fabricated based on μCT images of a Bentheimer core plug to mimic the reservoir conditions. As a result, in situ bacteria growth, biomass accumulation, biofilm formation and gas production were observed in the micromodel throughout the flooding experiments. During the injection, microbes were partly transported (planktonic) through the micromodel and the sessile attached to the model surface, causing a reduction in permeability (PRF). The results showed that the PRFs in artificial-structure micromodels are in line with the Kozeny–Carman model. Meanwhile biomass straining in small pore throats shows a more significant impact on the permeability reduction in real-structure micromodels. The injection of tracer particles after incubation showed a water flow diversion that confirmed bioclogging in the micromodels. The bioclogging evaluation presented in this work improved the understanding of the clogging process in porous media and can support ASR and EOR studies on a larger scale before field implementation

Experimental and Analytical Investigation of an Immiscible Displacement Process in Real Structure Micromodels

The recovery of oil from a reservoir can be accomplished with various methods, one of the most commonly applied types being waterflooding. A common theory used to describe immiscible displacement is the Buckley–Leverett theory. A brand new type of micromodel, generated and fabricated by using a micro-computer tomography (μCT) image stack of a real sandstone core, was used to conduct immiscible displacement experiments. Critical logging data were recorded, and a high-resolution camera took pictures of the displacement process. In an image processing tool (MATLAB), an algorithm was developed to evaluate the pictures of the experiment and to examine the changes in the saturations of the displacing and the displaced fluid. The main objective of the displacement experiment was to validate the new microchip in two-phase displacement experiments and to assess the feasibility of the image processing algorithm. This was performed by comparing the results of the experimental to the analytical solutions, which were derived from the Buckley–Leverett theory. The comparison of the results showed a good match between the two types of solutions. The applicability of the analytical results to the experimental procedures was observed. Additionally, the usage of the newly fabricated micromodel and its potential to visualize the fluid flow behavior in porous media were assessed