An integrated study for reservoir clogging: a pore scale to near well scale approach

In well abandonment programs, it is important to implement reliable measures to ensure the safe and secure blocking of wells. This process involves several steps, ultimately leading to the placement of cement barriers, which is the conventional method for sealing wells. However, before starting the cement installation, it is essential to establish a low downhole pressure to allow safe positioning of abandonment rigs near the platform. To achieve this, the porous media around the well should first be temporarily sealed to prevent fluid flow.

This study presents an integrated approach including an experimental investigation and modelling analysis to evaluate porous media clogging by bio-mineralization techniques. Microorganisms mediate crystal growth through various mechanisms, most of which eventually lead to the production of carbonate ions and increase the pH in the system. By introducing divalent ions such as calcium, different forms of carbonate crystals precipitate, which can clog the pore space. This study explores the kinetics of bio-clogging across different scales.

Chapter 2 investigates the kinetics of bio-mineralization in presence of nucleation sites. The main objective of these experiments is to quantify the influence of minerology on the kinetics of calcite precipitation. The results indicate that the presence of calcite crystals in the mineralization solution accelerates the precipitation rate of calcium carbonate. However, a negligible ureolysis is observed when the mineralization solution is equilibrated with cement. This slow ureolysis process is attributed to the potential denaturation of the enzyme in the high pH condition of the equilibrated solution.

Chapter 3 investigates the bio-clogging experiments in chalk samples with low and high permeability values. In these experiments, the clogging performance is analysed though enzymatically/microbially induced calcite precipitation (EICP/MICP) in intact and fractured chalk samples. It is indicated that a delayed precipitation is required to avoid clogging the inlet face of the carbonate cores. This is achieved by separating bacteria from the growth medium and suspending bacteria in milli-Q water, as well as injecting a water cycle as a barrier between the injection solutions. The experimental results indicate a limited bacterial penetration in chalk samples with low permeability values. However, bacterial penetration is achieved in core plugs with high permeability values, with a significant bacterial retention in porous medium during their transport. In the fractured core, the increasing trend in the recorded electrical conductivity values and calcium conversion factor indicated the rise in ureolytic activity over time, which confirmed a potential development of biofilm or accumulation of biomass in fractures. In high permeable core plugs, the conversion factor of calcium varies between 15 to 20 percent in the experimental condition implemented in this study. The EICP process in the homogeneous chalk media is simulated by implementing a reactive transport model in MATLAB Reservoir Simulation Toolbox (MRST). The simulation results suggest the deactivation of the accumulated enzyme and calcite precipitation close to the inlet of the core plug.

Chapter 4 focusses on the well-scale modelling of bio-clogging. The main objective of this chapter is to analyse how the change of various parameters influences the clogging performance around the wellbore. In the first step, the kinetic parameters of the biochemical reactions and the uncertain parameters associated with bacteria retention model are calibrated by simulating two sets of experimental data. The model is then applied for simulation of bio-clogging in different domains including linear flow in a two-layer domain and radial flow around an injection well in both 2D and 3D domains. In a two-layer domain, the impact of permeability contrast on clogging behaviour is discussed. In the radial flow, the biofilm distribution patterns across the porous medium are characterized as a function of salinity, flow rate, and bacterial concentration. The simulation results emphasize the importance of velocity decline in a radial domain on the change of biofilm formation and clogging behaviour across the system. Incorporating critical pore radius as a limiting factor for bacterial transport is shown to improve the accuracy of simulations regarding the clogging time in porous media with low and high permeability values. Additionally, the influence of heterogeneity on extending the clogging times is investigated and the impact of changing the treatment plans on bio-clogging performance is presented.

This study presents a comprehensive analysis of bio-clogging in porous media through both experimental analysis and mathematical modelling. It enhances our understanding of the impact of nucleation sites on precipitation kinetic and addresses the challenges associated with practical implementation of MICP/EICP process in chalk media. In the experiments, the permeability reduction values of 94% and 68% were achieved in homogeneous and fractured chalk samples, respectively. In addition, a well-scale modelling of bio-clogging is implemented that highlights the impact of different parameters on clogging behaviour in a radial domain.