Browsing by Subject "SP"
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Item Characterization of the MMTV-encoded Rem protein(2010-05) Ali, Almas Fatima, 1986-; Dudley, Jaquelin; Huibregtse, Jon M.Mouse mammary tumor virus (MMTV) is a betaretrovirus that causes mammary tumors in mice. MMTV is the only known complex murine retrovirus and encodes Rem, an HIV-1 Rev-like protein. Rem is a 301-amino-acid (33 kDa) protein that is cotranslationally targeted to the ER, where the first 98 amino acids constitute the signal peptide (SP). The SP is cleaved and retrotranslocated to the cytoplasm prior to nuclear entry. In this thesis, the results show that the presence of a leucine at position 71 allows more efficient cleavage of SP and increases Rem activity. Further, in Rem-transfected cells, the majority of SP appears in the nuclear fraction, consistent with fluorescent microscopy data. The C-terminal fragment of Rem (RemCT) is glycosylated in the ER and, although glycosylation sites are present outside the SP, mutations of both these sites abolish SP activity in a reporter assay. Indirect evidence suggests that unglycosylated RemCT is degraded by the proteasome, whereas glycosylated RemCT is likely secreted out of the cell. A variant of MMTV (TBLV) that lacks functional Sag and RemCT has been prepared and will be studied in mice to elucidate the role of RemCT in vivo. Development of an antibody to RemCT will allow tracking of the protein in virus-producing cells. Although there are many other similarities between complex retroviruses like HIV-1 and MMTV, current evidence suggests that Rem lacks an HIV Tat-like transactivator function.Item An experimental and simulation study of the effect of geochemical reactions on chemical flooding(2010-12) Chandrasekar, Vikram, 1984-; Delshad, Mojdeh; Pope, Gary A.The overall objective of this research was to gain an insight into the challenges encountered during chemical flooding under high hardness conditions. Different aspects of this problem were studied using a combination of laboratory experiments and simulation studies. Chemical Flooding is an important Enhanced Oil Recovery process. One of the major components of the operational expenses of any chemical flooding project, especially Alkali Surfactant Polymer (ASP) flooding is the cost of softening the injection brine to prevent the precipitation of the carbonates of the calcium and magnesium ions which are invariably present in the formation brine. Novel hardness tolerant alkalis like sodium metaborate have been shown to perform well with brines of high salinity and hardness, thereby eliminating the need to soften the injection brine. The first part of this research was aimed at designing an optimal chemical flooding formulation for a reservoir having hard formation brine. Sodium metaborate was used as the alkali in the formulation with the hard brine. Under the experimental conditions, sodium metaborate was found to be inadequate in preventing precipitation in the ASP slug. Factors affecting the ability of sodium metaborate to sequester divalent ions, including its potential limitations under the experimental conditions were studied. The second part of this research studied the factors affecting the ability of novel alkali and chelating agents like sodium metaborate and tetrasodium EDTA to sequester divalent ions. Recent studies have shown that both these chemicals showed good performance in sequestering divalent ions under high hardness conditions. A study of the geochemical species in solution under different conditions was done using the computer program PHREEQC. Sensitivity studies about the effect of the presence of different solution species on the performance of these alkalis were done. The third part of this research focused on field scale mechanistic simulation studies of geochemical scaling during ASP flooding. This is one of the major challenges faced by the oil and gas industry and has been found to occur when sodium carbonate is used as the alkali and the formation brine present in situ has a sufficiently high hardness content. The multicomponent and multiphase compositional chemical flooding simulator, UTCHEM was used to determine the quantity and composition of the scales formed in the reservoir as well as the injection and production wells. Reactions occurring between the injected fluids, in situ fluids and the reservoir rocks were taken into consideration for this study. Sensitivity studies of the effect of key reservoir and process parameters like the physical dispersion and the alkali concentration on the extent of scaling were also done as a part of this study.Item Experimental development of a chemical flood and the geochemistry of novel alkalis(2012-08) Winters, Matthew Howard; Pope, Gary A.; Weerasoriya, UpaliSurfactant-Polymer (SP) and Alkaline-Surfactant-Polymer (ASP) floods are tertiary oil recovery processes that mobilize residual oil to waterflood. These Chemical EOR processes are most valuable when the residual oil saturation of a target reservoir to waterflood is high. The first steps of designing a SP or ASP flood are performed in a laboratory by developing a surfactant formulation and by performing core flood experiments to assess the performance of the flood to recovery residual oil to waterflood. The two criteria for a technically successful laboratory SP or ASP core flood are recovering greater than 90% of residual oil to waterflood leaving behind less than 5% of residual oil and accomplishing this at a field scalable pressure gradient across the porous medium of approximately 1 psi per foot. This thesis documents the laboratory development of SP and ASP core floods for a continental Unites States oil reservoir reported to contain the minerals anhydrite and gypsum. The significance of these minerals is that they provide an infinite acting source of calcium within the reservoir that makes using the traditional alkali sodium carbonate unfeasible using conventional Chemical EOR methods. This is because sodium carbonate will precipitate as calcite in the presence of free calcium ions. Secondly, this thesis investigates two novel alkalis that are compatible with free calcium ions, sodium acetate and tetrasodium EDTA, for their viability for use in ASP floods for reservoirs containing anhydrite or gypsum.Item Experimental investigation of the effect of increasing the temperature on ASP flooding(2011-12) Walker, Dustin Luke; Pope, Gary A.; Weerasooriya, UpaliChemical EOR processes such as polymer flooding and surfactant polymer flooding must be designed and implemented in an economically attractive manner to be perceived as viable oil recovery options. The primary expenses associated with these processes are chemical costs which are predominantly controlled by the crude oil properties of a reservoir. Crude oil viscosity dictates polymer concentration requirements for mobility control and can also negatively affect the rheological properties of a microemulsion when surfactant polymer flooding. High microemulsion viscosity can be reduced with the introduction of an alcohol co-solvent into the surfactant formulation, but this increases the cost of the formulation. Experimental research done as part of this study combined the process of hot water injection with ASP flooding as a solution to reduce both crude oil viscosity and microemulsion viscosity. The results of this investigation revealed that when action was taken to reduce microemulsion viscosity, residual oil recoveries were greater than 90%. Hot water flooding lowered required polymer concentrations by reducing oil viscosity and lowered microemulsion viscosity without co-solvent. Laboratory testing of viscous microemulsions in core floods proved to compromise surfactant performance and oil recovery by causing high surfactant retention, high pressure gradients that would be unsustainable in the field, high required polymer concentrations to maintain favorable mobility during chemical flooding, reduced sweep efficiency and stagnation of microemulsions due to high viscosity from flowing at low shear rates. Rough scale-up chemical cost estimations were performed using core flood performance data. Without reducing microemulsion viscosity, field chemical costs were as high as 26.15 dollars per incremental barrel of oil. The introduction of co-solvent reduced chemical costs to as low as 22.01 dollars per incremental barrel of oil. This reduction in cost is the combined result of increasing residual oil recovery and the added cost of an alcohol co-solvent. Heating the reservoir by hot water flooding resulted in combined chemical and heating costs of 13.94 dollars per incremental barrel of oil. The significant drop in cost when using hot water is due to increased residual oil recovery, reduction in polymer concentrations from reduced oil viscosity and reduction of microemulsion viscosity at a fraction of the cost of co-solvent.Item Modeling, simulation and interpretation of spontaneous potential logs to quantify hydrocarbon saturation(2016-12) Bautista-Anguiano, Joshua Christopher; Torres-Verdín, CarlosThe Spontaneous Potential (SP) log has served for decades as a borehole correlation log and, under favorable circumstances, for the reliable in-situ assessment of water resistivity in rock formations of interest. Nevertheless, it is known from laboratory and field measurements that SP logs are sensitive to the presence of hydrocarbons. This report introduces the principles of SP log modeling using a mechanistic approach and describes their implementation in a SP log numerical simulator. Various synthetic and field cases verify the capabilities and improvement due to numerical modeling in the interpretation of SP logs. Quantification of hydrocarbon pore volume from SP logs is currently being validated with laboratory experiments. Those results and any modification to the models introduced in this document will be reported in a future doctoral dissertation. The main contribution and conclusions from this thesis originate from the presence of the electrical double layer (EDL) on the surface of mineral grains, its impact on SP measurements in the presence of hydrocarbons, and the utility and limitations it poses for the calculation of hydrocarbon pore volume and porosity. These petrophysical properties are independent of size. Thus, pore-size distribution and the volume of influence of the EDL in the pore space both determine whether SP logs will capture valuable information about hydrocarbon pore volume. Field cases are presented in which quantification of hydrocarbon pore volume is possible. Simulations made using the mechanistic principles presented in this work show consistency both in modeling and in comparison to measurements at the borehole scale. These field cases consider both water- and hydrocarbon-bearing formations in distinct petrophysical and geological environments. Calculations of hydrocarbon saturation and porosity are verified by the use of porosity and resistivity logs. The theory and results reported in this research highlight the importance of the EDL and the strong impact EDL has on improving interpretation of SP logs. Petrophysicists benefit from the possibility of mechanistically simulate SP logs that indicate the presence of hydrocarbon pore volume. This capability is useful in cases such as fresh-water environments where interpretation of resistivity logs may be problematic, or in mature hydrocarbon fields where only SP logs are available to the interpreter. The ability to simulate SP logs, particularly in mature hydrocarbon fields, offers a faster and less expensive way to evaluate new or overlooked gas or oil reservoirs.Item New method of predicting optimum surfactant structure for EOR(2011-12) Solairaj, Sriram; Pope, Gary A.; Weerassoriya, UpaliChemical enhanced oil recovery (CEOR) has gained a rapid momentum in the recent past due to depleting reserves of “easy-oil” and soaring oil prices. Hence, CEOR is now being considered for several candidates with varied oils and reservoir conditions, which demands the need for large hydrophobe surfactants. A new class of thermally and chemically stable large hydrophobe surfactant, Guerbet alkoxy carboxylates (GAC) has been tested. Unlike Guerbet alkoxy sulfates, GAC are stable at all pH and can be extremely useful in cases where alkali usage is prohibitive. They also exhibit synergistic behavior with internal olefin sulfonates (IOS) and alkyl benzene sulfonates (ABS), with the mixture showing enhanced calcium tolerance than the individual surfactants. Furthermore, in an attempt to diversify the raw material base, a new class of hydrophobe, viz. tristyrylphenol (TSP) based on petrochemical feed stock has also been developed and evaluated. Given the fact that there are hundreds of surfactants that can be tested for a particular candidate, the difficulty often lies in choosing the right surfactant to begin with. In an attempt to simplify that, a new correlation to predict the optimum surfactant structure has been developed. It relates the optimum surfactant structure to the formulation variables like oil properties, salinity, and temperature, including the parameters like PO and EO for new-generation surfactants. The correlation can serve as a guideline in choosing the optimum surfactant and will help in improving our understanding of the relationship among variables affecting the optimum surfactant structure. Surfactant retention is an important factor affecting the economics of chemical flooding and has to be studied carefully. Using an extensive data obtained from core flood studies a new correlation for predicting surfactant retention including the variables like pH, TAN, salinity, mobility ratio, temperature, co-solvent, and surfactant molecular weight has been developed. All these are new and highly significant advance in the optimization of chemical EOR processes that will greatly reduce the time and cost of the effort required to develop a good formulation as well as to improve its performance.Item Scale-up methodology for chemical flooding(2010-12) Koyassan Veedu, Faiz; Delshad, Mojdeh; Pope, Gary A.Accurate simulation of chemical flooding requires a detailed understanding of numerous complex mechanisms and model parameters where grid size has a substantial impact upon results. In this research we show the effect of grid size on parameters such as phase behavior, interfacial tension, surfactant dilution and salinity gradient for chemical flooding of a very heterogeneous oil reservoir. The effective propagation of the surfactant slug in the reservoir is of paramount importance and the salinity gradient is a key factor in ensuring the process effectiveness. The larger the grid block size, the greater the surfactant dilution, which in turn erroneously reduces the effectiveness of the process indicated with low simulated oil recoveries. We show that the salinity gradient is not adequately captured by coarse grid simulations of heterogeneous reservoirs and this leads to performance predictions with lower recovery compared to fine grid simulations. Due to the highly coupled, nonlinear interactions of the many chemical and physical processes involved in chemical flooding, it is better to use fine-grid simulations rather than coarse grids with upscaled physical properties whenever feasible. However, the upscaling methodology for chemical flooding presented in this work accounts approximately for some of the more important effects, as demonstrated by comparison of fine grid and coarse grid results and is very different than the way other enhanced oil recovery methods are upscaled. This is a step towards making better performance predictions of chemical flooding for large field projects where it is not currently feasible to perform the large number of simulations required to properly consider different designs, optimization, risk and uncertainty using fine-grid simulations.