In this study, effects of changes in various parameters of the Bayer process on the amount of &ldquo / red mud&rdquo / , which has many environmental drawbacks, were examined in accordance with the principles of &ldquo / sustainable development&rdquo / . The production process of SeydiSehir Aluminum Plant is modeled as a case study. First a steady-state mass balance calculation is carried out by incorporating sequential modular approach. Then a model of the Bayer process digester is programmed and several simulations are carried out using this model. Results of the mass balance calculation revealed that changes in the extent of the digestion reaction, which is a function of temperature and caustic concentration, and washing efficiency may have a 2.07% decrease on the amount of red mud produced,which implies nearly 10,000 tons of decline per annum, while amount of hydrate produced is increased by 4.52%. A 7.40 % decrease on the amount of red mud produced on dry basis per kg of hydrate was found to be achievable. Optimum operating temperature for the digester was calculated as 277.3 &deg / C.

Formation temperature is an important parameter in geothermal drilling since it affects all the components of the system such as drilling fluid, drilling operations and equipment through mud temperatures. The main objective of this study is to estimate the formation temperatures of five geothermal wells in Germencik-&Ouml / merbeyli geothermal field by using inlet and outlet mud temperatures obtained during drilling. For this purpose, GTEMP, a wellbore thermal simulation model is used to simulate the process of drilling and to estimate the formation and bit temperatures of five wells. With the formation and bit temperature estimations of GTEMP and inlet and outlet mud temperature data from field / temperatures vs. depth graphs are plotted for five wells for two cases. In Case 1, cooling tower effect on mud temperatures is neglected whereas in Case 2 it is taken into account. For the estimation of formation temperature of the final depth, Case 2 showed better results with % 1,5-24,5 deviation compared to the % 3,6-25,2 deviation obtained in Case 1.

Excessive torque is one of the most important problems in oil/gas drilling industry. Friction between wellbore/casing and drill string causes excessive torque. This study discusses performance analysis of drilling fluid lubricants, which are used as friction reducers in well-bore. Three different types of commercial chemical lubricants, which are fatty acid and glycerid based, triglycerid and vegetable oil based and polypropylene glycol based, diesel oil, and crude oil, which consists of different API gravity, paraffin and asphaltene value samples, were selected for the analysis. In the analysis, different lubricant compositions with the mixture of commercial chemical lubricants, crude oil and diesel oil, which were added to water based lignosulfonate mud, are tested on metal-metal contact surface by Ofite Lubricity Tester to determine the best lubricity/cost ratio of lubricant compositions. Moreover, effects of the lubricants on mud rheology and API fluid loss of mud, foam forming potential and cheesing/greasing of the lubricants and the influence of mud properties on lubricants (calcium, salt, pH and mud density) are examined.

none

Interpretation of 900 km of a closely spaced grid of high-resolution seismic profiles over the northwestern margin of South Caspian Basin (SCB) allows recognition and study of six late Pleistocene - Holocene depositional sequences. Sequence stratigraphy analysis of sedimentary strata from 117,000 years B.P. to present led to the identification of a highstand systems tract, two transgressive systems tracts and six lowstand systems tracts. Each systems tract is characterized by specific seismic facies. Diverse depositional processes on the northwestern margin of the SCB are suggested by the thirteen seismic facies patterns recognized in the study area. Two distinct progradational complexes were interpreted within Sequence III and Sequences IV and V in the northeastern and northwestern parts of the study area, respectively. Stratigraphic interpretation of the sequences provided important information on parameters that control depositional architectures, such as lake level fluctuations, tectonic dynamics, and sediment supply. High sedimentation rates combined with a series of high-frequency and high-amplitude lake-level fluctuations, abrupt changes at the shelf edge, abnormally high formation pressure, and high tectonic activity during Quaternary time resulted in the development of a variety of complex geologic drilling hazards. I distinguished three types of hazards as a result of this study: mud volcanoes, sediment instability, and shallow gas. The 2D high-resolution seismic dataset from the northwestern margin of the SCB allowed more detailed seismic sequence stratigraphic analysis in the study area than has previously been attempted. In particular, it has a clear application in deciphering sediment supply and relative lake level changes as well as tectonic relationship of the northwestern shelf margin of the SCB. Results of this work led us towards better understanding of recent depositional history, improved our knowledge of the nature of the basin tectonics, climate history and styles of and controls on sedimentation processes within a sequence stratigraphic framework during the late Pleistocene-Holocene time.

Understanding specific pathways for sand transport in the lower reaches of large rivers, particularly the Mississippi, is the key to addressing multiple significant geologic problems and for environmental restoration efforts. Field studies were performed in the Mississippi River 75-100 km upstream of the Gulf of Mexico outlet in April 2010 (water discharge: 23,000 m³ s⁻¹), May 2010 (18,500-20,500 m³ s⁻¹), and March 2011 (27,000 m³ s⁻¹) to examine sediment transport phenomena in the river channel. Methods comprised multibeam sonar bathymetric surveys, acoustic Doppler current profiler measurements of current velocity and acoustic backscatter, point-integrated isokinetic suspended sediment sampling, and channel-bed grab sampling. Channel morphology surveys revealed a 30-60 m deep thalweg, alternating between banks every 2-3 km, opposite bedform-covered lateral sand bars. Dune sizes nearest the thalweg ranged from 7 m wavelength and 0.3 m height to over 100 m wavelength and 2.3 m height as a function of water discharge, with decreasing dune sizes towards shallow water. Material comprising the dunes was well-sorted, 125-500 [mu]m sand. Bedload transport rates increased exponentially with water discharge in April 2010 and March 2011 comparable to previous studies in this reach, though rates in May 2011 were well below predicted values for a site (Myrtle Grove) immediately downriver of a sand-mining project. Average water velocities ranged from 1.3 m s⁻¹ in May 2010 to 2 m s⁻¹ in March 2011. Skin-friction shear stress increased with water discharge, but varied over an order of magnitude at all measured discharges. Suspended sand concentration and grain size increased with proximity to the bed during all study periods, and was most pronounced in March 2011. Suspended sand concentrations were greatest over the center of lateral bars, and lowest in the thalweg, indicating that sand transport downstream occurs primarily over lateral sand bars where there is a combination of high shear stress and available bed material. Total bed-material discharge increased exponentially with water discharge. Bedform-induced turbulence may be responsible for the bed material suspension. These results are relevant to coastal restoration efforts by river diversion which seek to distribute sand from the upper water column to deltaic interdistributary wetlands. / text

published_or_final_version / abstract / Mechanical Engineering / Doctoral / Doctor of Philosophy

Acidizing sandstone reservoirs is a complex process. If not fully studied, it could lead to formation damage. A combination of HCl/HF has been widely used to stimulate sandstone reservoirs. However, the success rate is low due to the complexity of the reactions involved in this process. These reactions result in potentially damaging precipitation and cause formation damage. The problem is more severe when dealing with Bandera sandstone formations that contain a high concentration of carbonate minerals and clay particles. The purpose of this study is to present and evaluate multi-stage acid injection into the Bandera sandstone cores to remove formation damage. In this study, coreflood experiments were conducted on Bandera sandstone cores (1.5 in. x 6 in.) at a flow rate of 4 cm^3/ min and temperature of 140°F. A mixture of formic acid and HF was used as an organic mud acid. Preflush of hydrochloric and formic acid was employed to remove carbonate minerals. Bandera sandstone cores contain a considerable amount of HCl sensitive clays. So another stage was employed to cover clay minerals and prevent HCl attack on the surface of clay particles. Different clay stabilizers as well as preflush pore volume were examined in this study. At the end, this multi-stage treatment design was tested on a Berea sandstone core to investigate the impact of mineralogy. During each experiment effluent samples were collected. Samples were analyzed using Inductively Coupled Plasma (ICP) and Scanning Electron Microscopy (SEM) to investigate reaction kinetics and chemistry of precipitation. Chemical analysis confirmed incompatibility of HCl with clays in Bandera cores at 140°F. Clay stabilizer CSA showed the ability to prevent HCl attack on the clay particle’s surface. As a result, a coreflood experiment conducted using CSA led to permeability improvement. The result of the coreflood experiment conducted using CSC indicated that this chemical is able to exchange cations with clay particles, however permeability decreased due to an insufficient injection of preflush. As in another experiment, increasing preflush pore volume using CSC resulted in permeability improvement. CSB completely failed to cover clay minerals and permeability decreased drastically at the end of the treatment.

In spread spectrum systems employing parity bit selected spreading sequences, parity bits generated from a linear block encoder are used to select a spreading code from a set of mutually orthogonal spreading sequences. In this thesis, turbo receivers for SS-PB systems are proposed and investigated. In the transmitter, data bits are rst convolutionally encoded before being fed into SS-PB modulator. In fact, the parity bit spreading code selection technique acts as an inner encoder in this system without allocating any transmit energy to the additional redundancy provided by this technique. The receiver implements a turbo processing by iteratively exchanging the soft information on coded bits between a SISO detector and a SISO decoder. In this system, detection is performed by incorporating the extrinsic information provided by the decoder in the last iteration into the received signal to calculate the likelihood of each detected bit in terms of LLR which is used as the input for a SISO decoder. In addition, SISO detectors are proposed for MC-CDMA and MIMO-CDMA systems that employ parity bit selected and permutation spreading. In the case of multiuser scenario, a turbo SISO multiuser detector is introduced for SS-PB systems for both synchronous and asynchronous channels. In such systems, MAI is estimated from the extrinsic information provided by the SISO channel decoder in the previous iteration. SISO multiuser detectors are also proposed for the case of multiple users in MC-CDMA and MIMO-CDMA systems when parity bit selected and permutation spreading are used. Simulations performed for all the proposed turbo receivers show a signi cant reduction in BER in AWGN and fading channels over multiple iterations.

Konstanz, Univ., Magisterarbeit, 2007.