RP-Department of Physics
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Browsing RP-Department of Physics by Author "Ambusso, W."
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Item 2D-Euler Deconvolution and Forward Modeling of Gravity Data of Homa-Hills Geothermal Prospect, Kenya(2014-02-25) Ambusso, W.; Odek, A.B.; Odek, A.; Githiri, J.G.In order to fully assess the potential of Homa Hills Geothermal prospect, the heat source which is one of the main features of a geothermal system had to be located based on its perturbation on the gravity field. Ground gravity survey was conducted in an area covering about 76 km2 and the data processed to remove all other effects which are not of geological interest. Qualitative interpretation was attempted and cross sections drawn across the anomalous areas on the complete Bouguer anomaly map. Quantitative interpretation attempted involved both Euler Deconvolution and 2‐D Forward modelling. The parameters obtained from Euler Deconvolution were used as the start up parameters for 2‐D Forward modeling. Well clustered Euler solutions were obtained at a shallow depth of approximately 200‐750 m which is consistent with the modeled shallow dike like intrusive probably of carbonatite origin.Item 2D-Forward Modeling of Ground Magnetic Data of Homa-Hills Geothermal Prospect Area, Kenya(SAGE Publications, 2014) Ambusso, W.; Githiri, J.; Abuga, V.; Odek, A.; Adero, B.Two dimensional (2D) Euler de-convolution techniques was applied on the selected profiles of reduced ground magnetic data collected in Homa Hills area. Depth estimates of causative bodies were quantitatively analysed in the an omalous areas on the residual magnetic intensity map. These depth estimates were later used as start up parameters for 2D-forward modelling using “mag2DC” software. Results of the analyses show that the magnetic anomalies in the region are caused by shallow-seated thermal intrusive structures of carbonatite origin. 2D-Euler solutions revealed subsurface faulting activities up to a depth of 250m and the presence of fluid-filled zones within the survey area which are marked by absence of magnetic sources. It is postulated from 2D-forward modelling that the heat sources are shallow intrusive bodies such as dykes, plugs and sills taping from a deeper magmatic body and that the thermal intrusive structures form along fracture zonesItem An algorithm for simulation of a Chemical Transport Equation in an Aquifer(2012) Ambusso, W.; Okiambe, E.; Mogwasi, R.Dynamical systems can be predicted using mathematical models. These models are usually Partial Different Equations (PDEs). Examples include the wave equation, equations for diffusive processes, and the heat conduction equation. Numerical solution of such PDEs describing a given system and its implementation using a suitable computer code can lead to numerous predictions on the dynamical system both in space and time. In this paper, the contaminant / chemical equation and the groundwater flow equation are solved numerically using the Integrated Finite Difference Method (IFDM) and the algorithms generated are simulated using an object oriented code. Generic results generated represent important predications on the fate and transport processes of a chemical in an aquiferItem Determination of Relative Permeability for Steam-Water Flow in Porous Media(Society of Petroleum Engineers, 1996-01-01) Ambusso, W.; Satik, C.; Horne, R.N.A set of relative permeability relations for simultaneous flow of steam and water in porous media were obtained from a steady state experiment. The experiment was conducted under conditions that minimize most of the difficulties encountered in the past for similar experiments. A high resolution X-ray CT scanner was used to obtain three-dimensional porosity and saturation distributions during the experiment. Pressure and temperature data were collected with the use of several pressure transducers and thermocouples located at various locations along the core. Relative permeability values were calculated over the core lengths identified as having flat saturation profiles. These aspects constitute a major improvement m the experimental method compared to those used in the past. The experimental results showed the relative permeability to both steam and water vary linearly with saturation, in contrast to those obtained by Corey (1954) for gas/water flow experiments. Comparison of the saturation profiles measured by the X-ray CT scanner during the experiments shows good agreement with those predicted by numerical simulation. To obtain results that are applicable to general flow of steam and water in porous media, similar experiments should be done at higher temperature and with porous rocks with different wetting characteristics and porosity distribution. Introduction In general, the concept of relative permeability is an attempt to modify Darcy's law for single-phase flow in porous media in order to account for simultaneous flow of multi phases. In this description the flow of each phase is governed by the individual microscopic pressure gradients and by the fraction of the overall permeability that is associated with it. This fraction, normally expressed as a fraction of the medium's permeability to a single-phase fluid, is called the relative permeability. Relative permeability relations have been traditionally expressed as a function of saturation principally because it was believed that they depended on the pore volume occupied by the fluids (Hassler, 1944). While a great number of experiments have shown this to be true, a number of other experiments have shown that relative permeability depends also on several other parameters such as interfacial tension, wetting characteristics and viscosity ratios of the flowing fluids etc. (Fulcher et al., 1983; Osoba et al., 1951). In addition it is necessary to define residual saturations which normally indicate the lowest saturation value for a given phase to become mobile. The curves and the residual saturations together define the relative permeability relations (Corey, 1954; Brooks and Corey, 1964). For most applications in petroleum engineering involving the flow of oil and water as in water flooding and the flow of oil and gas as in gas injection, the relative permeability relations are well known and determined routinely from laboratory experiments (Osoba et al., 1951). However, for the flow of steam and water or for the general case of multi component multi phase flows these relations are not well known. A look at previous literature shows that there is a significant discrepancy and inconsistency in the results previously obtained (Verma, 1986; Sanchez, 1987; Clossman and Vinegar, 1988). The main difficulties encountered in the previous experiments, as we show later in this paper, have been mainly due to inaccurate measurements of fluid saturations and inappropriate assigninent of pressure gradients to the individual phases. Techniques involving analysis of enthalpy transients from producing geothermal fields have been proposed to infer relative permeability relations (Grant, 1977; Sorey et al., 1980; Horne and Ramey, 1978).Item A Numerical Solution to Estimate Hydro-geologic Parameters of a Fractured Geothermal Porous Medium Based on Fluorescein Thermal Decay Correction(Elsevier, 2014-07-31) Ambusso, W.; Rathore, I.; Omenda, P.; Okiambe, E.; Wang’ombe, B.A numerical solution to model the flow of fluorescein tracer in a fractured, high temperature geothermal system is presented. This study was carried out in Olkaria, Kenya. Results show that correcting for fluorescein decay at elevated temperatures can be used to yield reservoir hydro-geologic parameters and improve the methods of evaluating effects of injected fluids on reservoir temperature. The hydro-geologic parameters for this study are better than those obtained by other methods. This outcome was obtained by solving the material, tracer and energy balance equations that were fully discretized using integral finite difference and solved by Gauss–Seidel recursive methods. A computer code in C++ had to be written to perform the simulations. Porosity and permeability were seen to range between 11 and 16% and 1.8–2.6 Darcy respectively. Reservoir pore volume along well OW-12 and OW-19 flow path was approximately 17–26 million litres whilst recharge rate was 7 kg/s. This proves that computational methods such as those considered here can be used for industrial application. Furthermore, fluorescein being cheap and benign to environment can be made applicable in high temperature geothermal systems.Item A Preliminary Study of Relative Permeability in Geothermal Rocks Authors(Geothermal Resources Council, Davis, CA (United States), 1995-12-31) Ambusso, W.; Satik, C.; Castanier, L.M.; Horne, R.N.This paper reports preliminary experimental and numerical efforts towards obtaining steam-water relative, permeability and capillary pressure functions under steady-state and adiabatic conditions. In the experimental direction, steady-state nitrogen-water relative permeability experiments were conducted in a Berea sandstone core as a first step. Results obtained from this type of experiment will be compared to those from steam-water relative permeability experiments in order to explore the importance of phase change and heat transfer. Using a high resolution X-ray computer tomography (CT) equipment, saturation distributions along the core were obtained and relative permeabilities for both nitrogen and water were calculated. Preliminary results showed strong end effects for the core length and total flow rate used in the experiment, which therefore suggested either to use of a longer core or to work at a higher total flow rate. Along with the experiment, numerical simulations of simultaneous injection of steam and water into a core were also carried out by using a commercial thermal simulator. At steady-state flow conditions, effects of steam quality and total injection rate on saturation profiles were investigated. Numerical simulation results suggested a core length of 38.10 cm for a flat saturation profile region to exist under typical experimental conditions.Item Removal of Fluoride from Aqueous Solutions by Adsorption using a Siliceous Mineral of a Kenyan Origin(WILEY‐VCH Verlag, 2013-04-01) Wambu, E.W.; Onindo, C.O.; Ambusso, W.; Muthakia, G. K.The problem of high fluoride in water sources in Africa and the rest of the developing world has exacerbated in the latest past due to increasing shortage of water. More people are being exposed to high water fluoride resulting in elevated levels of fluorosis in the societies. Fluoride (F) adsorption from solutions using a siliceous mineral from Kenya (M1) was studied on batch basis and results verified on high fluoride water using fixed-bed column experiments. About100% batch F adsorption wasachieved at 200mg/L F concentration, 0.5g/mL adsorbent dosage, 303–333K, and pH 3.4 0.2. Based on Giles classifications, F adsorption isotherm was found to be an H3 type isotherm. The equilibrium data was correlated to Freundlich and Langmuir models and the maximum Langmuir adsorption capacity was found to be 12.4mg/g. Column experiments were conducted for different fluoride concentrations, bed depths, and flow rates. The F breakthrough curves were analyzed using the Thomas model and efficient F adsorption was found to occur at low flow rates and low influent concentrations. The Thomas F adsorption capacity (11.7mg/g) was consistent with the Langmuir isotherm capacity showing that M1 could be applied as an inexpensive medium for water defluoridationItem Removal of Fluoride from Aqueous Solutions by Adsorption using a Siliceous Mineral of a Kenyan Origin(WILEY‐VCH Verlag, 2013-04-01) Ambusso, W.; Muthakia, G. K.; Onindo, C.O.; Wambu, E.W.The problem of high fluoride in water sources in Africa and the rest of the developing world has exacerbated in the latest past due to increasing shortage of water. More people are being exposed to high water fluoride resulting in elevated levels of fluorosis in the societies. Fluoride (F) adsorption from solutions using a siliceous mineral from Kenya (M1) was studied on batch basis and results verified on high fluoride water using fixed-bed column experiments. About100% batch F adsorption wasachieved at 200mg/L F concentration, 0.5g/mL adsorbent dosage, 303–333K, and pH 3.4 0.2. Based on Giles classifications, F adsorption isotherm was found to be an H3 type isotherm. The equilibrium data was correlated to Freundlich and Langmuir models and the maximum Langmuir adsorption capacity was found to be 12.4mg/g. Column experiments were conducted for different fluoride concentrations, bed depths, and flow rates. The F breakthrough curves were analyzed using the Thomas model and efficient F adsorption was found to occur at low flow rates and low influent concentrations. The Thomas F adsorption capacity (11.7mg/g) was consistent with the Langmuir isotherm capacity showing that M1 could be applied as an inexpensive medium for water defluoridation