Controlling the risk of cross-contamination from the building drainage system using the reflected wave technique to identify depleted water trap seals

The appliance trap seal remains the primary defence against cross-contamination from the foul air present within the building drainage system. As an identified vector in the spread of severe acute respiratory syndrome (SARS) in Hong Kong in 2003, trap seal failure has been confirmed as a significant, and potentially fatal, risk to public health. Prevention of trap seal failure depends upon both good design, to limit the air pressure transients propagated within the system, and good maintenance. However, current maintenance regimes rely solely on visual inspections which is time consuming and often impractical to implement in large complex buildings. This thesis documents the development of a novel approach to system maintenance whereby the threat of cross-contamination of disease is minimised by the remote monitoring of trap seal status. This was approached through the application and development of the reflected wave technique which is fundamentally based upon the characteristic reflection coefficients of system boundary conditions. An extensive programme of laboratory experiments and field trials were carried out to collect transient pressure data which, together with results from an existing mathematical model (AIRNET), developed by the Drainage Research Group at Heriot- Watt University, have been used to validate the proposed technique and to formulate a practical methodology which may be applied to any building drainage system. Automatic system diagnosis, which would in the future allow the proposed technique to be integrated as an automated system test, was provided by the development of the trap condition evaluator (TRACER) program by this author. Incorporating a time series change detection algorithm, the TRACER program accurately detects and locates a depleted trap seal by automatically identifying the return time of the trap’s reflection. The reflected wave technique has been demonstrated as a successful approach to depleted trap identification provided that the wave propagation speed is known and the dampening influence of the junction effect (which can delay the observed reflection return time) are taken into account. The reflected wave technique offers a remote and non-invasive approach to maintaining the building drainage system and provides, for the first time, a diagnostic tool to help prevent cross-contamination.Engineering and Physical Sciences Research Council (EPSRC

Immiscible and miscible gas-oil displacements in porous media

Gas Injection is the second largest EOR process in U.S. To increase the extent of the reservoir contacted by displacing fluids, gas and water are injected intermittently - water-alternating-gas (WAG) process, is widely practiced. This experimental study is aimed at evaluating the WAG process performance in short and long cores as a function of gas-oil miscibility and brine composition. This performance evaluation has been carried out by comparing oil recoveries between WAG injection and continuous gas injection (CGI). Miscible (2500 psi) and immiscible (500 psi) floods were conducted using Berea cores, n-Decane and two different brines, namely the commonly used 5% NaCl solution and another the multicomponent brine from the West Texas Yates reservoir. Each of the ten corefloods consisted of series of steps including brine saturation, absolute permeability determination, flooding with oil (drainage) to initial oil saturation, flooding with brine (imbibition) to residual oil saturation, and finally, tertiary gas injection to recover the waterflood residual oil. It was found that comparing tertiary gas floods only on the basis of recovery yielded misleading conclusions. However, when oil recovery per unit volume of gas injection was used as a parameter to evaluate the floods, miscible gas floods were found more effective (recovery 60-70% higher) than immiscible floods. The WAG mode of injection out-performed the CGI floods. At increased gas volume injection, the performance of miscible CGI flood, inspite of the high injection pressure, approached the immiscible floods. A change in brine composition from 5% NaCl to 9.26% multivalent Yates reservoir brine showed a slight adverse effect on tertiary gas flood recovery due to increased solubility of CO2 in the latter. While immiscible WAG floods in short cores donot show appreciable improvement over CGI immiscible floods, WAG recovery was 31% higher than 6-ft CGI floods. The results of this study prompted a new process by combining CGI and WAG modes of gas injection. Such a process was found patented and practiced in the industry. In addition to providing performance characteristics of the WAG process, this study has indicated directions for further research aimed at improving oil recovery from gas injection processes

Optimum horizontal well length considering reservoir properties and drainage area

The length of a horizontal well increases and so does its drainage area. The efficiency of the long horizontal well is no longer proportional to the length of the well, since the rise in the length of horizontal well output segment also tends to causes frictional pressure losses in the well. Nevertheless, there are currently no reliable standards which take into account quantitatively the parameters necessary to determine the optimum well length of horizontal drilling. A new strategy to the basic productivity index is introduced, taking into account the friction losses under influx conditions in a long manufacturing segment. The consequence of this special productivity index is the constant state flow in an anisotropic structure of a very compressible fluid. This paper presents a technique developed to achieve an optimum length of horizontal pool based on the shift in the overall economics and productivity index (PI) in the long horizontal wellbore with frictional loosing results. In order to achieve optimal overall efficiency in a horizontal well project, an integrated method is proposed for numerical analysis of the parameters that affect profitability using Computer Modelling Group reservoir simulation (CMG)

One-dimensional modelling of mixing, dispersion and segregation of multiphase fluids flowing in pipelines

The flow of immiscible liquids in pipelines has been studied in this work in order to formulate a one-dimensional model for the computer analysis of two-phase liquid-liquid flow in horizontal pipes. The model simplifies the number of flow patterns commonly encountered in liquid-liquid flow to stratified flow, fully dispersed flow and partial dispersion with the formation of one or two different emulsions. The model is based on the solution of continuity equations for dispersed and continuous phase; correlations available in the literature are used for the calculation of the maximum and mean dispersed phase drop diameter, the emulsion viscosity, the phase inversion point, the liquid-wall friction factors, liquid-liquid friction factors at interface and the slip velocity between the phases. In absence of validated models for entrainment and deposition in liquid-liquid flow, two entrainment rate correlations and two deposition models originally developed for gas-liquid flow have been adapted to liquid-liquid flow. The model was applied to the flow of oil and water; the predicted flow regimes have been presented as a function of the input water fraction and mixture velocity and compared with experimental results, showing an overall good agreement between calculation and experiments. Calculated values of oil-in-water and water-in-oil dispersed fractions were compared against experimental data for different oil and water superficial velocities, input water fractions and mixture velocities. Pressure losses calculated in the full developed flow region of the pipe, a crucial quantity in industrial applications, are reasonably close to measured values. Discrepancies and possible improvements of the model are also discussed. The model for two-phase flow was extended to three-phase liquid-liquid-gas flow within the framework of the two-fluid model. The two liquid phases were treated as a unique liquid phase with properly averaged properties. The model for three-phase flow thus developed was implemented in an existing research code for the simulation of three-phase slug flow with the formation of emulsions in the liquid phase and phase inversion phenomena. Comparisons with experimental data are presented

Life Cycle Modelling of Carbon Dioxide Capture and Geological Storage in Energy Production

Carbon dioxide (CO2) capture and geological storage (CCS) is recognised as one of the main options in the portfolio of greenhouse gas (GHG) mitigation technologies being developed worldwide. The CO2 capture and storage technologies require significant amounts of energy during their implementation and also change the environmental profile of power generation. The holistic perspective offered by Life Cycle Assessment (LCA) enables decision makers to quantify the trade-offs inherent in any change to the power production systems and helps to ensure that a reduction in GHG emissions does not result in significant increases in other environmental impacts. Early LCA studies of power generation with CCS report a wide range of results, as they focus on specific CO2 capture cases only. Furthermore, previous work and commercial LCA software have a rigid approach to system boundaries and do not recognise the importance of the level of detail that should be included in the Life Cycle Inventory (LCI) data. This research developed a complete LCA framework for the “cradle-to-grave” assessment of alternative CCS technologies in carbon-containing fuel power generation. A comprehensive and quantitative Life Cycle Inventory (LCI) database, which models inputs/outputs of processes at high level of detail, accounts for technical and geographic differences, generates LCI data in a consistent and transparent manner was developed and arranged and flexible structure. The developed LCI models were successfully applied to power plants with alternative post-combustion chemical absorption capture and oxy-fuel combustion capture. The results demonstrate that most environmental impacts come from power generation with CCS and the upstream process of coal production at a life-cycle perspective. LCA results are sensitive to the type of coal used and the CO2 capture options chosen. Moreover, the models developed successfully trace the fate of elements (including trace metals) of concern throughout the power generation, CO2 capture, transport and injection chain. Monte Carlo simulation method combined with the LCI models was applied to quantify the uncertainty of emissions of concern. A novel analytical framework for the LCA of CO2 storage was also developed and applied to a saline aquifer storage field case. The potential CO2 leakage rates were quantified and the operational and geological parameters that determine the ratio of CO2 leakage total volume of CO2 injected were identified