Suresh Kumar Govindarajan

Leachate from municipal solid waste landfill contains a variety of contaminants including organic acids. The subsequent vertical movement of organic acids from the landfill may reach and pollute the groundwater. Hence, the prediction of vertical movement in the unsaturated sub-surface system is essential to monitor the groundwater contamination. To achieve this, a one-dimensional numerical model has been developed to understand and forecast the transport of organic acids in unsaturated soil using a finite difference technique. This study considers acetic acid as a representative organic compound in the landfill leachate. The Richards equation is used to simulate the water content in the unsaturated soil and advection–dispersion equation is used to predict the transport of organic acid. Moreover, first-order decay coefficient is also considered during the migration of organic acid. The numerical results suggest that the transport of organic acid is strongly influenced by water content variation in the unsaturated subsurface. Further, it is also observed that the soil distribution coefficient was found to be one of the most influencing parameters, which is significantly affecting the organic acid concentration profile in the unsaturated soil. Moreover, the decay coefficient is also affecting the distribution of organic acid in the vadose zone. Overall, the numerical results show that the higher simulation time allows the concentration of organic acid to reach larger depth. Hence, there is a high probability of groundwater contamination by organic acid concentration.

In-Situ Combustion (ISC) thermal Enhanced Oil Recovery (EOR) methods are aimed at increasing the oil recoveries of heavy oil reserves that are expected to play an instrumental role in near future in meeting the world's energy demand. The complex multiphase heat and reactive mass transport necessitate a clear understanding of thermal and kinetic models used in modeling of ISC process. A finite difference based numerical analysis is carried out on heat loss and selective productions of light oil components during ISC, which showed a significant effect on peak temperature, thermal front propagation and the corresponding production rates dictating the performance of ISC process. © (2014) Trans Tech Publications, Switzerland.

The process of injection and withdrawal from tight gas reservoirs is a multiphysics and multicomponent problem. The aim of the present work is to capture the physics associated with the injection of CO2 into tight shales, and assess and mitigate the risks associated with reservoir overpressure. The overpressure caused by CO2 injection usually triggers the onset of formation–deformation, which inadvertently affects the state of the stress in the target geological formations and its surroundings, the monitoring of which is critical to understand the risks in conjunction with CO2 storage. In the present work, a novel fully coupled fully implicit flow and geomechanics simulator is introduced to describe the physics in conjunction with an extended injection phase of CO2. The developed model solves for pressure saturation and porosity and permeability changes considering a multicomponent system while principally focusing on the adsorption and diffusion of CO2 and stress-dependent reservoir deformation employing cell-centred finite volume method. It is envisaged that the injection of CO2, while with the primary purpose of storage, will parallelly enhance the recovery from shale gas due to lateral sweep effects. Based on these mechanisms, for the case study of a tight gas field, the applicability of the simulation model is tested for formations with varied rock and fluid moduli in a 20-year simulation period.

Any successful primary cementing operation at elevated temperature condition requires an efficient displacement of fluid surrounding the casing by cement slurry. In such conditions the cement slurry should be designed in such a way that it should be compatible with both cement and drilling mud. To achieve these requirements we designed the cement slurry with weighted spacer. Spacer is a barrier between cement & mud so that they should not mix with each other, also all these fluids should be incompatible inorder to avoid cement aggregation. The displacement efficiency during cementation is directly dependent on discharge rate, but however due to formation fracture pressure constraints, the discharge rate is limited, hence designing spacer becomes very crucial. This phenomenon becomes more pronounced at higher temperature as turbulent flow efficiency reduces due to the presence of weighting agent. The drive of the present work is to identify a suitable viscosifier to avoid settling of weighing agents in spacer and to maintain the stability of rheology admixture at elevated temperature condition. Laboratory tests were performed for compatible deformation and flow of matter with cement slurry-spacer-mud at temperature range (80-140°C) on a rotational viscometer as per the procedure of API RP 10B-2. The volumetric proportions of the cement slurry/spacer and spacer/mud admixtures were prepared with various ratios: 95/5, 75/25, 50/50, 25/75, and 5/95. Rheological compatibility of fluids (cement & spacer and mud & spacer) is evaluated by computing the R-Index Value (R) which is calculated by subtracting highest 100 rpm reading of admixture from highest rpm reading for an individual fluid for the given range of elevated temperature condition. The calculated R-Index Value can then be utilized to comment on fluid compatibility. After finalization of chemical compatibility, rheological hierarchy was achieved by incorporating the friction pressure loss with respect to discharge rate of an individual fluid for the given range of elevated temperature condition. The spacer system used achieved stable compatibility and efficient rheological hierarchy at elevated temperature cementing conditions. In addition, by comparing the results between the two different spacer systems, the role of hydration in attaining rheological compatibility is computed. This study will in turn prove helpful in figuring out the better spacer system which will play a vital role for better displacement and cementation quality.

Clay minerals present within the groundwater aquifers is found to influence the migration of hazardous solutes like radionuclides and petroleum hydrocarbons. The presence of clay minerals within the aquifers is observed to either enhance or retard the movement of contaminants within the aquifer. The influence of these clay minerals on the contaminant migration depends upon the hydrologic conditions existing within the aquifer, nature of contaminants, kind of clay minerals, etc. Previous research studies have illustrated the significance of clay minerals on the migration of petroleum hydrocarbons (PHC) within the aquifers. Sorption of petroleum hydrocarbons on aquifer grains and colloid particles is a significant factor in deciding the mitigation rate of hydrocarbons. The primary objective of the present study is to numerically investigate the clay-associated transport of petroleum hydrocarbons within a saturated aquifer. The current modeling algorithm can be adapted to model the colloid-facilitated transport of other multicomponent contaminants within the fracture. The modeling algorithm is solved using a C++ program. In the present paper, simulation results for the concentration distribution of clay mineral and PHC within the aquifer are presented. Sensitivity of clay attachment and detachment rates on the concentration distribution of PHC and clay minerals are also analyzed.

Petroleum contamination in groundwater is a widespread and well-known global environmental problem, mainly due to the leaking of aged pipelines or storage tank. The in situ treatment of petroleum hydrocarbons is relatively difficult to perform especially during pump-and-treat technique due to the trapped low-soluble hydrocarbons in the soil pores. The solubility enhancement and improved bioavailability of the small solvable portions in the petroleum products such as polycyclic aromatic hydrocarbon (PAH) can be performed by surfactants. This study aims to understand the enhanced mobility on PAH (phenanthrene) with the availability of surfactants and the associated physicochemical interactions in the saturated porous media. A 1D model is established in this regard to study the impact of surfactant on PAH enhanced solubility and subsequent transport in the saturated porous system. The hydraulic properties of soil, equilibrium partitioning and all reactions on the fate and movement of PAH are carefully included in this work. The results show that a considerable increase in the aqueous phase PAH concentration during the availability of surfactant (Triton N-101). In addition, the influence of partitioning between aqueous and solid phase, biodegradation, oxygen mass transfer are showing substantial variation on PAH transport in the saturated zone. The developed numerical model can be efficiently useful for the prediction of low-soluble organic fraction during the in situ remediation of petroleum hydrocarbon contamination.

The subsurface contamination by petroleum hydrocarbons (PHC) from leaking underground storage tanks, pipelines and refilling stations is one of the serious issues directly affecting the quality of groundwater. Application of advanced oxidation process (AOP) has been favoured for the remediation of petroleum contaminated sites due to the spontaneous redox reactions mediated by a strong activating agent. In this study, we propose a methodology for efficient injection of reagents by using two concentric PTFE tubes in a sand box model for simulating the groundwater flow, contaminant transport and in situ chemical oxidation (ISCO) using Fenton’s reagents (hydrogen peroxide and zero-valent iron particles). This injection method has proved to maximize the interaction of chemicals resulting in complete oxidation of petroleum compounds. An attempt has also been made to numerically simulate the mass transfer and transport of petroleum hydrocarbons incorporating the impact of spontaneous mass transfer by means of numerical methods. It is expected to have significant difference in interface mass transfer between free phase (oil) and water leading to increased exposure of residual oil phase, thereby enhancing the complete mass removal. The presence of soil organic matter (SOM) is found to be enhancing the activity of Fenton’s reagents as well as increasing the adsorption of hydrophobic organic compounds.