Engineering: Recent submissions
Now showing items 61-80 of 522
-
Permeability characterization of Schrader Bluff Sands using artificial neural networks"Permeability is a fundamental and often difficult to predict property of any reservoir. This is especially true for unconsolidated formations where any type of physical permeability measurement is difficult. This study develops a more detailed picture of reservoir permeability by generating continuous predicted permeability logs for the Schrader Bluff sands. Schrader Bluff sands are a medium heavy oil reservoir currently produced from the Milne Point oil field on the Alaska North Slope (ANS). A total of about 400 ft of core samples from two Milne Point wells were analyzed using a probe permeameter. These data were then integrated with available permeability data and used along with electric well log data for training an Artificial Neural Network to obtain continuous predicted permeability logs. The predicted data were then used to make Modified Lorenz Plots to study the flow unit behavior and to identify possible flow units. A similar dual approach that includes both probe permeameter measured and predicted permeability data can be used for flow unit characterization in other reservoirs with deficient permeability datasets. This approach would be especially useful for permeability characterization of unconsolidated or semiconsolidated reservoirs"--Leaf iii
-
Analysis of wind-diesel hybrid option in Buckland, Deering and Noorvik villages of Alaska"The high cost of energy in remote off-grid villages of Alaska is a major concern for Alaska. The primary cause is due the relatively high cost of fuel transportation to the remote villages. A hybrid technology of wind power combined with diesel power is one option for reducing costs. The wind-diesel hybrid technology has already been implemented successfully in some remote villages; however this technology is not yet mature and presents many site-specific considerations. This thesis presents a techno-economic feasibility analysis for three villages currently considering implementing wind-diesel technology. The analysis was principally performed using HOMER, an energy modeling software tool. HOMER was used to perform an optimization and sensitivity analysis of wind-diesel hybrid systems for Buckland, Deering and Noorvik villages in Alaska. HOMER uses the hourly wind speed and electric load data from the villages, and performs an energy balance analysis to optimize the equipments sizes and system design based on the minimum life cycle cost. Based on input specifications used, the results obtained indicate that a high-penetration system is optimum for Noorvik, a medium or low-penetration system is optimum for Derring, and none of the wind-diesel systems investigated here would reduce the cost of energy in Buckland"--Leaf iii
-
Winds and the meteors that burn for them"Meteors typically ablate from 70-130 km in altitude leaving in their wake a trail of ionized plasma that moves with the surrounding neutral winds. Once formed, these trails are visible to impinging radar signals. This thesis utilizes meteor plasma trail observations made by the Kodiak, Alaska, SuperDARN radar over 2004 and 2005 to develop a technique for the estimation of mesospheric-lower thermospheric (MLT) winds and tides and demonstrate the capabilities of the SuperDARN radar in advancing MLT science"--Leaf iii
-
Numerical modeling for in-stream hydrokinetic resources assessment"During recent years the viability of extracting river energy using hydrokinetic devices became a topic that brought in national attention due to higher fuel costs, and an increased demand of electric energy. A tool for hydrokinetic energy potential assessment in rivers, HYDROKAL, which stands for Hydrokinetic Calculator, was developed. This tool was generated in Fortran 90 programming language as an external module for the CCHE2D, an existing two-dimensional hydrodynamic numerical model developed by researchers at the National Center for Computational Hydroscience and Engineering, University of Mississippi. Velocity outputs generated by the CCHE2D model are used by HYDROKAL to estimate instantaneous power density, an essential element in calculating the hydrokinetic power of a river. For each model cross section, maximum velocity and specific discharge are also identified. These maximum values could provide insights on the stability of the river reach and, thus, the feasibility of installing an in-stream turbine. A Python script is provided to allow the export of results from HYDROKAL to CCHE2D. HYDROKAL was applied on a Tanana River reach near Nenana, AK, where the possibility of installing an in-stream device is being explored. River velocities obtained from an Acoustic Doppler Current Profiler were used to validate the model"--Leaf iii.
-
An implementation of a numerical advection equation solver on modern graphics cards using compute unified device architecture"In the past decade, the Graphics Processing Unit (GPU) is reported to have become a powerful general-purpose computation platform for various application areas. The Arctic Region Supercomputing Center (ARSC) intends to assess the capability of this emerging computing tool so that they may enlist it as component of supercomputing systems, but at a lower cost. This thesis reports on parallelization, on both GPU and CPU, of a numerical algorithm named the Total Variation Diminishing (TVD) scheme, which is used in the Eulerian Polar Parallel Ionospheric Model (EPPIM) developed at UAF's Geophysical Institute (GI) and ARSC. The GPU (single NVIDIA Tesla® C2050) and CPU (dual Intel Xeon x5560) implementations were parallelized using the Compute Unified Device Architecture (CUDA) language and OpenMP with the C language respectively. A speedup of up to 175x was observed when comparing the CUDA/GPU implementation to the non-parallelized CPU version, and of almost 40x when comparing to the parallelized CPU version. Results also demonstrated an average floating-point-operation rate of 107 GFLOPs, 351 times more than that the CPU version can offer. However, there is still space for improvement as only one tenth of the peak theoretical performance of the C2050 was achieved"--Leaf iii.
-
Characterization of subsurface hydraulic conductivity along the proposed Alaska Gas Line Corridor using geophysical signatures"The objective of this research was to explore a cost-effective and non-invasive methodology to characterize spatial variability of hydraulic conductivity using airborne electromagnetic (AEM) signatures as an alternative to traditional techniques such as borehole sampling. The relationship of AEM measured apparent resistivity and magnetic field strength was explored using a small dataset that included 180 natural moisture (NM) content data and a total dataset of 546 grain size distributions that excluded the NM. The grain size distributions were used to develop soil indicator parameter and to estimate the hydraulic conductivity (K*) using pedo-transfer functions. Predictive models were developed using three techniques; artificial neural network regression (ANNR), support vector regression (SVR), and artificial neural network classification (ANNC). The sole use of non-invasive parameters to characterize K* proved insufficient. The inclusion of supplemental invasively collected parameters showed ANNR to best characterize the relationship (R² = 0.64) with the smaller dataset; while the SVR model performed best with the total dataset (R² = 0.57). ANNC was shown to be a viable alternative (overall accuracy = 88%) when broad characterization of K* was sufficient. This study lays out a methodology that could be used for future K* characterization using improved data set"--Leaf iii.
-
Application of nanoparticle saturated injectant gases for enhanced oil recovery of heavy oils"Heavy oil, an immense U.S. oil resource, is untapped because its highly viscous nature makes it challenging to produce. The high cost and additional time associated with heavy oil production make it uneconomical compared with light oil production. Currently, heavy oil reservoir production challenges are mostly addressed by thermal recovery techniques. These techniques are generally successful because heat 'thins' heavy oil by reducing its viscosity. Carbon dioxide (CO₂) flooding is a well-known tertiary production technique used in depleted oil reservoirs. Supercritical CO₂ (SC-CO₂) dissolves in trapped oil and reduces oil viscosity by swelling it. More oil pushes towards the production well, with improved ability to move through pores in the rock. Metal nanoparticles are used for thermal conductivity enhancement of fluids. This thesis describes work carried out on copper oxide (CuO) metal nanoparticles, a sc-CO₂ soluble surfactant, and SC-CO₂. In another set of experiments, Viscosity Reducing Injectant (VRI), a miscible injectant used by Alaska North Slope operators, was used along with metal nanoparticles. The advantages of three different processes- thermal, chemical, and gas injection were merged together to devise a novel viscosity reducing process for heavy oil from the Alaska North Slope (ANS). ANS heavy oil displacement experiments were performed with metal nanoparticles and SC-CO₂ to determine the recovery factor of ANS heavy oil as compared to SC-CO₂ alone. A threefold reduction in viscosity and almost 22% increase in recovery factor were observed when metal nanoparticles, surfactant and SC-CO₂ were used as compared to SC-CO₂ alone"--Leaf iii
-
Liquefaction potential and post-liquefaction settlement of saturated clean sands: and effect of geofiber reinforcement"Liquefaction of saturated granular soils has been the cause of most geotechnical hazards during earthquakes. Development of excess pore pressures in saturated soils when subjected to cyclic loading has been shown to cause the liquefaction, which can be simply described as the transformation of stable soil structure into unstable liquid form. Majority of the previous laboratory studies have been focused on stress-controlled loading. However, the generation of excess pore pressure is better characterized by the induced shear strains. The objectives of this study were: (i) to investigate the liquefaction potential and post-loading volumetric strain of saturated clean sands through strain-controlled testing; and (ii) to study as an alternative mitigation technique, the influence of geofiber reinforcement on exess pore pressure generation and post-liquefaction settlement of saturated sands. Undrained, strain-controlled, cyclic triaxial tests were performed in the following categories: (1) tests performed under different effective consolidation stresses; (2) tests performed at various number of loading cycles; (3) tests performed at different relative densities; and (4) tests performed on geofiber-reinforced sand specimens. The liquefaction potential of specimens subjected to different levels of shear strains were investigated with respect to the developed excess pore pressures. Reduction in the volume of the specimens with the dissipation of generated excess pore water pressure was studied by allowing for drainage after cyclic loading. Additionally, the influence of geofibers as a possible mitigation measure against the excess pore pressure development and post-loading volumetric straining of clean sands was investigated. The results from this study were used to develop insight into the behavior of clean and geofiber-reinforced sands under seismic loading conditions. Based on the test results, geofiber-reinforced seismic loading conditions was found that the number of loading cycles has significant influence on the generation of excess pore pressure and post-loading volumetric strain. Specimens subjected to continued loading after initial liquefaction indicated about three times larger volumetric strains when compared to those allowed to drain after initial liquefaction. Soil specimens consolidated to 100kPa effective stress were found to experience less volumetric strain than that observed in specimens consolidated to 400kPa effective consolidation stress; however, the excess pore pressure generation at 100kPa effective stress was about two times larger than that measured at 400kPa effective stress. In general, geofiber-reinforced specimens showed less excess pore pressures when compared to clean sand specimens; while post-loading settlement were observed to be nearly two times larger for specimens with 1%geofiber content when compared to clean sand specimens"--Leaves iii-iv
-
Rhizoremediation of diesel contaminated soil using Salix alaxensis"An outdoor pot study and a microcosm study were conducted to evaluate the potential for Salix alaxensis (felt leaf willow) to rhizoremediate diesel-contaminated soil. The pot study was conducted for 96 days during an Alaskan interior summer with S. alaxensis grown in soil contaminated with diesel fuel oil #2. The concentration of diesel range organics (DRO) and the most probable number (MPN) of diesel degrading microorganisms in the rhizosphere were measured initially and compared to final values. A microcosm study was also performed with crushed willow roots to simulate root turnover, in which the abundance of diesel degrading microorganisms was also determined. It was hypothesized that treatments containing willow and fertilizer would foster the greatest abundance of diesel degrading microorganisms and thus would provide the largest decrease of diesel range organics. In the pot study, growth of S. alaxensis resulted in the largest decrease of DROs, although treatments amended with fertilizer contributed to a significant increase in MPN of diesel degrading microorganisms. The microcosm study indicated that the addition of crushed willow roots to contaminated soil produced a similar abundance of diesel degrading microorganisms as the addition of salicylic acid. The findings suggest that S. alaxensis can be a useful plant for rhizoremediation of diesel-contaminated soil"--Leaf iii
-
Microfiltration membrane material properties and surface water characteristics: effects on membrane fouling2010-05"Surface water can be challenging to treat due to high concentrations of organic matter. Membrane filtration produces high quality effluent but membrane fouling reduces system efficiency. A bench-scale, dead end filtration system was used to investigate the fouling effects of natural source waters on microfiltration flat sheet membranes. Membrane materials were selected to represent a range of surface charge characteristics and hydrophobicity. The source waters included an arctic lake, a subarctic river, as well as modified water samples, pre-filtered to include only the dissolved organics, or with deliberately changed pH values. Bench-scale results were compared with a pilot-system's seasonal performance. Resistance was shown to increase linearly over time. A resistance model was a good fit to bench scale membrane filtration runs. Membrane material was shown to be more important to membrane fouling than pH or season. Overall the charged, hydrophilic membranes performed the best, with the lowest fouling rate. Hydrophobic membranes had the highest fouling rate. Solution pH was found to affect membrane fouling rates. Influent pH adjustment improved filtration performance for some source waters and not others. The pilot system performance would have been improved by pH adjustment"--Leaf iii
-
Variably saturated flow and heat transport simulations of an Interior Alaskan fen"The objectives of this research are: to identify the applicably and limitations of a one-dimensional coupled model to simulate variably saturated hydrologic and energy transport processes in peat; to assess the sensitivity of the hydrologic input parameters and water fluctuations on heat transport; and to test an in situ frequency domain method of soil freezing characteristics versus a statistical approach. Soil temperatures and energy transfer through soils and hydrology are interrelated. Chemical, macro- and microbiological activities are largely dependent on both of these processes in peatlands. It is important to model these processes to assess the interaction of hydrology and soil temperature dynamics under current and future climate conditions. Modeling was accomplished using the van Genuchten model for soil moisture characteristics and hydraulic conductivity, coupled with thermal conduction, convection, and latent heat to study the effects of the vadose zone on heat transfer in peat. The model was calibrated with 40 days of data from 2005, in a fen site in Interior Alaska. Diurnal model verification was conducted with data from 2006, 2008, and 2009. The results of this study demonstrated that the coupled numerical solutions applied to the fen performed well over a variety of environmental conditions. The application of a statistical method of characterizing variably saturated processes suggested variability in moisture distribution in the unsaturated zone. Errors in winter simulations were most likely caused by hysteresis indicating a need for a non-symmetric solution to compensate for the latent heat of phase change in ice"--Leaf iii
-
Using synthetic aperture radar (SAR) to estimate bathymetry and volume of shallow North Slope lakes"An efficient and cost effective method of monitoring North Slope lakes is essential for balancing the needs of industrial and environmental consumers. Arctic lakes are necessary for supporting facility and drilling operations. They are also integral parts of the Arctic ecosystem. Lakes are advantageous sites for long term monitoring of climate change. Remote sensing is a cost effective tool for sustained monitoring of this large and inaccessible environment. Synthetic Aperture Radar (SAR) was used in conjunction with the Modified Stefan's ice thickness equation to estimate bathymetry and volume of three North Slope lakes. A series C-band SAR images taken over the 2000-2001 winter were processed to differentiate between grounded and floating ice. The ice thickness of each pixel was estimated by recording the date it became grounded and the corresponding ice thickness of that date. Ice thickness was used to determine water depth, which was used to create bathymetric maps and estimate volume. The bathymetric estimates using the SAR methodology for lakes S0901, S0902 and S0903 produced an 18.08% underestimate, 19.06% underestimate and a 6.53% overestimate, when compared to ground truthed bathymetry. These results demonstrate that this method can be used for reliable, low cost evaluation of these important resources"--Leaf iii
-
Damage modeling of carbon-fiber reinforced polymer at extreme temperatures2010-08"A finite element model was generated to study how thermal stress influences damage progression in carbon-fiber reinforced composite laminates using a double shear bearing joint model. Quasi-static damage was observed using a progressive damage method that incorporated Hashin type damage criteria. Material properties for FiberCote T700/E765 24K unidirectional carbon fiber were used to create three material models with properties corresponding to the ambient temperatures -55, 20 and 82 °C. The joint strength was predicted using a 2% bearing strain offset method. At -55 °C ambient temperature, joint strength was reduced 8.6% as the relaxation (stress-free) temperature was varied from 20 to 100 °C. At 82 °C ambient temperature, joint strength was reduced 3.6% as the relaxation temperature was varied from 20 to 100 °C. Increasing the relaxation temperature decreased the joint strength and increased the matrix tensile damage rate but did not greatly affect other failure modes"--Leaf iii
-
Stochastic connectivity analysis of low sinuosity streams and statistical analysis of representative petrographic data from tertiary tight gas sands, Cook Inlet, Alaska"Tight gas sands present a considerable development challenge due to reservoir heterogeneity and poor permeability. Successful exploitation of tight gas reservoirs requires an understanding of the factors controlling their porosity and permeability (P & P) as well as the geological factors influencing the distribution of key facies. Initial statistical analysis of published petrographic data of Cook Inlet tight gas prospects reconfirmed the effect of mechanical compaction on porosity. A suitable correlation between porosity and depth for very fine to fine (VF-F) grain tight gas sandstone was developed. Though permeability was weakly correlated with porosity, the positive effect of macropore (>20 microns across) percentage on permeability was evident. Thus, a suitable permeability-macropore correlation was developed for non-cemented, VF-F grain, and fine-medium to medium grain sandstone samples. These results help clarify the factors that control the porosity and permeability of Cook Inlet tight gas prospects. Static connectivity and effective static connectivity analysis of stochastic channel facies model representing low sinuosity river deposits, as found in the Cook Inlet Region in Alaska, shows the high uncertainty involved in static connectivity analysis at lower channel facies volume percentage. However, channel deposits of sinuosity 1.1 show best static connectivity with a drainage area of 50 acres. Above 70%-75% of channel volume, the role of channel dimension in static connectivity is limited and 100% static connectivity is achievable. This facies modeling assists in predicting the factors that control the static connectivity of low sinuosity tight gas reservoirs in Kenai Group of Formations. Moreover, this static connectivity analysis will help determine recommended well spacing and well type, orientation, and suitable completion techniques to enhance recovery efficiency in Cook Inlet tight gas sands"--Leaf iii
-
Impact of fines content on resilient modulus reduction of base courses during thawing"Resilient modulus (MR) of base course material is an important material input for pavement design. In Alaska, due to distinctiveness of local climate, material source, fines content and groundwater level, resilient properties of D-1 granular base course materials are significantly affected by seasonal changes. The presence of fines (P₂₀₀) affects frost susceptibility of base materials and controls the aggregates' ability to support vehicular load, especially during the spring-thaw period. To systematically evaluate the impact of fines content on the resilient properties of D-1 base course materials with varied fines content, gradation, moisture content and temperature during thawing and provide regression coefficients ki which are required for the flexible pavement design, a laboratory investigation was conducted on D-1 materials from Northern, Central, and Southeast Regions of Alaska Department of Transportation and Public Facilities (AKDOT & PF) at different temperatures, moisture and fines contents. MR data were determined by conducting repeated triaxial tests on D-1 materials with fines content ranging from 3.15% to 10% and moisture content from optimum moisture contents (OMC) -2% to OMC+0.7%, respectively. For MR tests at subfreezing temperatures, a frost heave cell was designed and fabricated for specimen preparation. To simulate the natural frost heave in winter, aggregate specimens experienced a freezing process by using frost heave cell. The designed frost heave cell is an open system which allowed free water intake during freezing process. Frost heave data and change of moisture contents after the freezing process were obtained from frost heave tests. Frost heave test results indicated that most of frost heave values were less than 3 mm for D-1 materials with fines contents ranging from 3.15% to 10%. The frost heave could be affected by initial moisture contents of aggregate specimens. MR tests results showed that MR decreased with an increase of moisture content. Within the scope of this study, impact of fines content varied which were affected by moisture contents of aggregate specimens. At subfreezing temperatures, there was a significant increase of MR when compared with room temperature. Impacts of fines and initial moisture content on MR values were weakened due to the change of moisture and aggregate structure after freezing process. Temperature was found to be an important factor influencing MR of D-1 materials, especially when temperature ranged from -5 °C to 0 °C. As temperature decreased, MR increased. However, when temperature was decreased to -5 °C, MR values seemed to be stable and further change of temperature did not result in any significant change of MR. Resilient properties of D-1 materials at room temperature after one freeze-thaw cycle were also investigated in this study. The reduction of MR after the freeze-thaw cycle was inevitable and significant, especially for aggregate specimens with high fines contents. Regression equations were also developed to correlate MR values with the physical properties (moisture and fines contents), stress states, and temperature conditions of D-1 materials. For D-1 materials tested in this study, at room temperature, MR was found to be a function of stress state, moisture and fines contents. At subfreezing temperatures, MR was a function of deviator stress, temperature, and aggregate type. These equations obtained can be used to predict MR values of Alaskan D-1 materials for pavement design"--Leaf iv
-
Evaluation of the loss of functionality of xanthan gum based drill-in fluid and its impact on coiled tubing drilling"A challenge that has recently arisen in coiled tubing drilling is the loss of functionality of xanthan gum drill-in fluid with drilled depth in the well. The overall objective of this study is to analyze and assess the causes for this loss of optimal functionality. Twenty-four field samples from two field cases and five laboratory prepared samples were tested to study the changes in theological parameters, salinity effects and compatibility with shale formations. It was observed that the fluid's functionality was directly related to low shear rate viscosity, which is affected by xanthan gum concentration and the ionic strength of the solution. X-ray diffraction analysis revealed a loss in the ionic strength due to the depletion of potassium chloride (KCI) with drilled depth. Experimental laboratory work confirmed the decrease in fluid viscosity as a result of KCI depletion. This decrease could result in a reduction of the cuttings carrying capacity of the drill-in fluid. A major implication of this work was the understanding gained on the reduced compatibility between xanthan gum solutions and the encountered shale formations; this happens due to KCI loss. As a result, possible stuck pipe conditions could be encountered if the reduced compatibility is left unaddressed"--Leaf iii
-
Numerical heat transfer model of a traditional ice cellar with passive cooling methodsPermafrost ice cellars have been used for generations by Arctic communities for subsistence food storage. Many of these ice cellars have been recently reported to be difficult or impossible to maintain due to thawing and water accumulation inside the cellar. The thesis objective is to investigate the effectiveness of implementing passive techniques to lower the surrounding permafrost temperature, ideally to 0°F, the USDA recommended temperature, throughout the year. Numerical finite element modeling was used to investigate the effects on permafrost temperature with the addition of two-phase, closed thermosyphons and/or ground insulation. Thermosyphon condensers installed both above and below ground were studied. The numerical models were created using Comsol Multiphysics. The modeling results indicated that the addition of thermosyphons and insulation caused a decrease in permafrost temperatures surrounding the ice cellar, although the target temperature of 0°F could not be maintained throughout the year by any of the methods studied. Subsurface insulation decreased the amplitude between the minimum and maximum temperature of the cellar wall 4.5°C. Air thermosyphons decreased the average temperature 8.5°C, and with additional insulation, 90C. Ground thermosyphons were less effective, decreasing the average wall temperature 2.4°C. Additionally, thermosyphon performance was found to be rate-limited by conduction through permafrost.
-
Fluid characterization and phase behavior studies of oil from the frozen reservoir of Umiat Oil Field, AlaskaUmiat oil field is the largest oil accumulation in National Petroleum Reserve (NPRA) No. 4 of Alaska. Shallow reservoir depths, low reservoir pressures, and low temperatures with most of the oil-producing zone in a continuous layer of permafrost are unique characteristics that make Umiat reservoir unconventional and difficult to produce. However, unavailability of fluid characterization and phase behavior data needed for reservoir simulation studies pose challenges in developing an effective production strategy. Given the conspicuous lack of complete fluid data on Umiat oils and the unavailability of live oil samples from Umiat, an experimental study was undertaken to characterize and quantify phase behavior of an available small volume of dead Umiat oil. The oil composition characterized experimentally was found to be severely weatherized and not representative of original Umiat oil. Comparison of components in the dead oil sample origina one characterized by Pedersen method enabled determination of the mass of each component that would be need to be added to the weathered sample in order to compensate for the evaporated light ends. The re-created sample was subsequently used for constant composition expansion (CCE) laboratory PVT test. The bubble point pressure at reservoir temperatures, and densities and viscosities of single-phase reservoir fluid at various pressures were measured. The phase behavior of the pseudo live oil was also simulated using Peng-Robinson equations of state (PR-EOS). The EOS model was tuned with measured experimental data to simulate differential liberation tests in order to obtain the PVT data needed for reservoir simulation studies.
-
Investigation of a landslide in discontinuous permafrost near Chitina, AlaskaFew studies have investigated landslides in frozen ground. As Alaska's population grows and climate warms, we can expect an increase in landslide frequency. This thesis presents mapping and subsurface analysis of a slide occurring in discontinuous permafrost near Chitina, Alaska. The active slide intersects the McCarthy Road and occurs within an underlying clayey glaciolacustrine diamicton deposit in an area previously used as a dump. The multifaceted investigation included landslide feature mapping, seismic surveys, tree-ring sampling, and a slope stability analysis to back-calculate residual soil strength properties. Mapping indicated that the overall landslide extent is larger than the active slide area. Analysis of tree-rings suggested movement occurred as at least two events. Seismic surveys produced good correlation with drilling data and effective subsurface imaging. Boring logs indicated that the permafrost table was at greater depth inside the active slide area than immediately adjacent along the roadway. These observations indicate that the failure mechanism for the active portion of the slide is different than that of the overall slide area. Back-calculation of the clay properties indicates a residual effective friction angle of 22.1 Permafrost degradation due to thermal effects of the dump may contribute to ongoing movement of the active slide area.
-
Production modeling and forecasting of natural gas production from Barrow methane hydrate depositsIn this work, state-of-the-art existing simulation models of East Barrow and Walakpa natural gas fields with associated gas hydrates were rebuilt, tuned with additional data (some of the data used were from the Mt. Elbert Well, which significantly improved earlier models), and updated in terms of production data and history matching. Fluid contacts, saturations and hydrate dissociation/formation reactions were initialized for both models, actual production was matched and planned wells were placed accordingly. For each model, a gas hydrate saturation sensitivity study was performed. Simulation models were run and production forecasts for Walakpa field were made. There is a clear picture of East Barrow field behavior, but the Walakpa model still involves significant approximations. Additional log data from new wells planned in the Walakpa field will reduce reservoir properties uncertainty and make the model a more realistic reservoir management tool. A well choking study was performed on a hypothetical simplistic radial simulation grid with a vertical well. It was discovered that vertical gas wells drilled close to a hydrate zone tend to die due to hydrate blockage. Higher gas rates revealed improved production, but faster flow rate decline because of hydrate reformation. Horizontal wells could mitigate this problem due to their lower pressure drop per unit length of completed interval. They are also capable of higher production at lower drawdown. Since higher rate causes faster choking due to hydrate reformation, intermittent reduction of the flow rate is recommended for vertical wells in order to mitigate or at least delay the choking problem. Overall, both horizontal and vertical well designs are suitable for natural gas production from hydrate reservoirs.