The flow of homogeneous fluids through porous media: analogies with other physical problems

http://cds.cern.ch/record/994225/files/0610327.pdf

Four-dimensional string compactifications with D-branes, orientifolds and fluxes

We construct a cubic field theory which provides all genus amplitudes of the topological A-model for all non-compact toric Calabi-Yau threefolds. The topology of a given Feynman diagram encodes the topology of a fixed Calabi-Yau, with Schwinger parameters playing the role of Kahler classes of the threefold. We interpret this result as an operatorial computation of the amplitudes in the B-model mirror which is the quantum Kodaira-Spencer theory. The only degree of freedom of this theory is an unconventional chiral scalar on a Riemann surface. In this setup we identify the B-branes on the mirror Riemann surface as fermions related to the chiral boson by bosonization.

/pdf/the-topological-vertex-3lrad1kwkt.pdf

The Topological Vertex

Let G be a split semisimple algebraic group over Q with trivial center. Let S be a compact oriented surface, with or without boundary. We define positive representations of the fundamental group of S to G(R), construct explicitly all positive representations, and prove that they are faithful, discrete, and positive hyperbolic; the moduli space of positive representations is a topologically trivial open domain in the space of all representations. When S have holes, we defined two moduli spaces closely related to the moduli spaces of G-local systems on S. We show that they carry a lot of interesting structures. In particular we define a distinguished collection of coordinate systems, equivariant under the action of the mapping class group of S. We prove that their transition functions are subtraction free. Thus we have positive structures on these moduli spaces. Therefore we can take their points with values in any positive semifield. Their positive real points provide the two higher Teichmuller spaces related to G and S, while the points with values in the tropical semifields provide the lamination spaces. We define the motivic avatar of the Weil–Petersson form for one of these spaces. It is related to the motivic dilogarithm.

/pdf/moduli-spaces-of-local-systems-and-higher-teichmuller-theory-36h32nsutb.pdf

Moduli spaces of local systems and higher Teichmüller theory

We discuss systematic approaches to the classification of string/M theory vacua, and physical questions this might help us resolve. To this end, we initiate the study of ensembles of effective Lagrangians, which can be used to precisely study the predictive power of string theory, and in simple examples can lead to universality results. Using these ideas, we outline an approach to estimating the number of vacua of string/M theory which can realize the Standard Model.

https://iopscience.iop.org/article/10.1088/1126-6708/2003/05/046/pdf

The statistics of string/M theory vacua


 In an era of increasing energy demand, declining oil fields, and fluctuating crude oil prices globally, most oil companies are looking forward to implementing cost-effective and environmentally sustainable enhanced oil recovery (EOR) techniques such as low salinity waterflooding (LSWF) and microbial EOR (MEOR). The present study numerically investigates the combined influence of simultaneous LSWF and microbial flooding for in-situ MEOR in tertiary mode within a sandstone core under spatiotemporally varying pH and temperature conditions.
 The developed black oil model consists of five major coupled submodels: nonlinear heat transport model; ion transport coupled with multiple ion exchange (MIE) involving uncomplexed cations and anions; pH variation with salinity and temperature; coupled reactive transport of injected substrates, Pseudomonas putida and produced biosurfactants with microbial maximum specific growth rate varying with temperature, salinity, and pH; relative permeability and fractional flow curve variations owing to interfacial tension (IFT) reduction and wettability alteration (WA) by LSWF and biofilm deposition. The governing equations are solved using finite difference technique. Operator splitting and bisection methods are adopted to solve the MIE-transport model.
 The present model is found to be numerically stable and agree well with previously published experimental and analytical results. In the proposed MIE-transport mechanism, decreasing injection water (IW) salinity from 2.52 to 0.32 M causes enhanced Ca2+ desorption rendering rock surface toward more water-wet. Consequently, oil relative permeability (kro) increases with >55% reduction in water fractional flow (fw) at water saturation of 0.5 from the initial oil-wet condition. Further reducing IW salinity to 0.03 M causes Ca2+ adsorption shifting the surface wettability toward more oil-wet, thus increasing fw by 52%. Formation water (FW) salinity showed minor impact on WA with <5% decrease in fw when FW salinity is reduced from 3.15 to 1.05 M. During low-salinity augmented microbial flooding (LSAMF), biosurfactant production is enhanced by >63% on reducing IW salinity from 2.52 to 0.32 M with negligible increase on further reducing IW and FW salinities. This might be owing to limiting nonisothermal condition (40 to 55°C), dispersion, sorption, and microbial decay. During LSAMF, maximum biosurfactant production occurs at microbial maximum specific growth rate of 0.53 h-1, mean fluid velocity of 2.63×10-3 m h-1 and initial oil saturation of 0.6, thus resulting in significant WA, increase in kro by >20%, and corresponding fw reduction by >84%. Moreover, the EOR efficiency of LSAMF is marginally impacted even on increasing the minimum attainable IFT by two orders of magnitude from 10-3 to 10-1 mN m-1. Though pH increased from 8.0 to 8.9, it showed minor impact on microbial metabolism. Formation damage owing to bioplugging observed near injection point causing increase in fw by ~26% can be mitigated by adopting suitable well-stimulation strategies during the LSAMF run time.
 The present study is a novel attempt to show synergistic effect of LSAMF over LSWF in enhancing oil mobility and recovery at core scale by simultaneously addressing complex crude oil-brine-rock (COBR) chemistry and critical thermodynamic parameters that govern MEOR efficiency within a typical sandstone formation. The present model with relatively lower computational cost and running time improves the predictive capability to preselect potential field candidates for successful LSAMF implementation.

Numerical Investigation on Low-Salinity Augmented Microbial Flooding within a Sandstone Core for Enhanced Oil Recovery under Nonisothermal and pH Gradient Conditions

Darcy’s law is widely used to describe the steady-state laminar incompressible single-phase fluid flow in a fully saturated porous medium at the macroscopic-scale. However, in reality, we will be dealing with transient non-laminar compressible multi-phase fluid flow through a saturated porous medium. In this context, it is important to understand the original framework of Darcy’s law; and subsequently, we need to understand clearly, under what circumstances the classical Darcy’s law was extended in order to consider the (a) the differential form of Darcy’s law; (b) the non-linear relation between pressure gradient and fluid velocity; (b) the transient nature of fluid flow; (c) the fluid flow through heterogeneous and anisotropic reservoirs or aquifers. It has been reemphasized from the present study that the presence of weak inertial effect along with the laminar fluid regime causes the ‘non-linear’ relation between the macroscopic pressure gradient and the macroscopic fluid velocity, while the strong inertial effect paves the way for the onset of transient nature of fluid flow.

/pdf/darcy-s-experimental-empirical-relation-and-its-extension-3w0c38iq80.pdf

Darcy’s experimental empirical relation and its extension

We compute the partition function for the topological Landau-Ginzburg B-model on the disk. This is done by treating the worldsheet superpotential perturbatively. We argue that this partition function as a function of bulk and boundary perturbations may be identified with the effective D-brane superpotential in the target spacetime. We point out the relationship of this approach to matrix factorizations. Using these methods, we prove a conjecture for the effective superpotential of Herbst, Lazaroiu and Lerche for the A-type minimal models. We also consider the Landau-Ginzburg theory of the cubic torus where we show that the effective superpotential, given by the partition function, is consistent with the one obtained by summing up disk instantons in the mirror A-model. This is done by explicitly constructing the open-string mirror map.

Effective superpotentials for B-branes in Landau-Ginzburg models

In the present work, fully coupled dynamic thermo-hydro-geo-mechanical model was employed to investigate the advantage and disadvantages of supercritical CO2(SCCO2) over water as geofluids. Low-temperature zone was found in both SCCO2-EGS and water-EGS systems, but spatial expansion is higher in water-EGS. Although, the spatial expansion of SCCO2 into the rock matrix will help in the geo-sequestration. The expansion of stress and strain invaded zones were identified significantly in the vicinity of fracture and injection well. SCCO2-EGS system is giving better thermal breakthrough and geothermal life conditions compared to the water-EGS system. Reservoir flow impedance (RFI) and heat power are examined, and heat power are high in the water-EGS system. Minimum RFI is found in the SCCO2-EGS system at  and 0.05 m/s. Maximum heat power for SCCO2-EGS was observed at , 20 MPa, and 0.15 m/s. Therefore, the developed dynamic THM model is having greater abilities to examine behavior of SCCO2-EGS and water-EGS systems effectively. The variations occur in the rock matrix and the performance indicators are dependent on the type of fluid, injection/production velocities, initial reservoir pressure, injection temperature. The advantages of SCCO2-EGS system over the water-EGS system, providing a promising result to the geothermal industry as geofluid.

Comparison of Supercritical CO 2 with Water as Geofluid in Geothermal Reservoirs with Numerical Investigation Using Fully Coupled Thermo-Hydro-Geomechanics

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.

Suresh Govindarajan

Papers

Numerical Investigation on Low-Salinity Augmented Microbial Flooding within a Sandstone Core for Enhanced Oil Recovery under Nonisothermal and pH Gradient Conditions

Darcy’s experimental empirical relation and its extension

Effective superpotentials for B-branes in Landau-Ginzburg models

Comparison of Supercritical CO 2 with Water as Geofluid in Geothermal Reservoirs with Numerical Investigation Using Fully Coupled Thermo-Hydro-Geomechanics

Modeling Investigations on Sorption of Petroleum Hydrocarbons to Clay Minerals in a Saturated Porous Aquifer