Browsing by Subject "Permeability"
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Item A laboratory analysis of cement permeability of typical cement mixtures used in the Permian Basin(2007-08) Deshmukh, Viraj; Siddiqui, Shameem; Heinze, Lloyd R.; Ziaja, MalgorzataIn the Petroleum Industry today, downhole cement plays an important role during drilling & production operations. It is responsible for lending strength to the casing for future production, it helps in preventing collapse of the formation, as well as restricts fluid movement between permeable zones. This downhole cement however, has different problems in the field from inadequate compressive strength, early setting of slurry etc. But of all these problems, sulfate attack on downhole cement is probably the biggest one facing the industry today. Another problem in use of different cement slurries has been the traditional lack of research for cement permeability, which has the biggest influence on the degree of this sulfate attack. Thus Texas Tech University & BJ Services have thus carried out a new study in my thesis, where we have studied & analyzed how sulfates in water react with the dry cement initially by measuring this initial permeability. Thus a study has also been carried out in measuring cement permeability of typical cement slurries used in the Permian Basin, something not yet documented & recorded officially before. This will give us a better understanding of cement properties for future reference.Item Analysis of HMA permeability through microstructure characterization and simulation of fluid flow in X-ray CT images(Texas A&M University, 2005-02-17) Al Omari, Aslam Ali MuflehThe infiltration of water in asphalt pavements promotes moisture damage primarily through damaging the binder cohesive bond and the adhesive bond between aggregates and binder. Moisture damage is associated with excessive deflection, cracking, and rutting. The first step in addressing the problems caused by the presence of water within pavement systems is quantifying the permeability of hot mix asphalt (HMA) mixes. This dissertation deals with the development of empirical-analytical and numerical approaches for predicting the permeability of HMA. Both approaches rely on the analysis of air void distribution within the HMA microstructure. The empirical-analytical approach relies on the development of modified forms of the Kozeny-Carman equation and determining the material properties involved in this equation through three dimensional microstructure analyses of X-ray Computed Tomography (CT) images. These properties include connected percent air voids (effective porosity), tortuosity, and air void specific surface area. A database of materials and permeability measurements was used to verify the developed predicting equation. The numerical approach, which is the main focus of this study, includes the development of a finite difference numerical simulation model to simulate the steady incompressible fluid flow in HMA. The model uses the non-staggered system that utilizes only one cell to solve for all governing equations, and it is applicable for cell Reynolds number (Rec) values that are not restricted by |Rec|≤2. The validity of the numerical model is verified through comparisons with closed-form solutions for idealized microstructure. The numerical model was used to find the components of the three-dimensional (3-D) permeability tensor and permeability anisotropy values for different types of HMA mixes. It was found that the principal permeability directions values are almost in the horizontal and vertical directions with the maximum permeability being in the horizontal direction.Item Centrifuge measurement of two-phase transient flow in rigid porous media(2016-08) Blake, Calvin; Zornberg, Jorge G.; Mohanty, Kishore KGravity driven multi-phase flow in porous media is an important mode of fluid transport in several geologic settings. Some applications where gravity drainage may play an important role in the movement of a fluid can include primary oil recovery from a petroleum reservoir or water flow into the ground surface. Because of the similarities between a single-gravity environment and a centrifugal environment, measurements of two-phase flow are often conducted in the centrifuge to observe the behavior of the whole system under gravity-like conditions while reducing the time of measurement. In this study, measurements of transient fluid outflow from sandstone cores were conducted in the centrifuge using air as the invading phase. The draining phase in these experiments comprised three different brines and a light mineral oil. Hydraulic conductivity functions and capillary pressure curves were determined from this data using a numerical history matching technique, and the results were compared with two prevailing analytical models. The results of this study corroborate previous findings that a full numerical history match can easily predict more realistic hydraulic conductivity functions than the prevailing analytical models.Item Cleanup of internal filter cake during flowback(2005) Suri, Ajay; Sharma, Mukul M.Item Complexity in river-groundwater exchange due to permeability heterogeneity, in-stream flow obstacles, and river stage fluctuations(2011-05) Sawyer, Audrey Hucks; Cardenas, Meinhard Bayani, 1977-; Catania, Ginny; Hodges, Ben; Mohrig, David; Reible, DannyRiver-groundwater exchange (hyporheic exchange) influences temperature, water chemistry, and ecology within rivers and alluvial aquifers. Rates and patterns of hyporheic exchange depend on riverbed permeability, pressure gradients created by current-obstacle interactions, and river stage fluctuations. I demonstrate the response of hyporheic exchange to three examples of these driving forces: fine-scale permeability structure in cross-bedded sediment, current interactions with large woody debris (LWD), and anthropogenic river stage fluctuations downstream of dams. Using numerical simulations, I show that cross-bedded permeability structure increases hyporheic path lengths and modifies solute residence times in bedforms. The tails of residence time distributions conform to a power law in both cross-bedded and internally homogeneous riverbed sediment. Current-bedform interactions are responsible for the decade-scale tails, rather than permeability heterogeneity. Like bedforms, wood debris interacts with currents and drives hyporheic exchange. Laboratory flume experiments and numerical simulations demonstrate that the amplitude of the pressure wave (and thus hyporheic exchange) due to a channel-spanning log increases with channel Froude number and blockage ratio (log diameter : flow depth). Upstream from LWD, downwelling water transports the river’s diel thermal signal deep into the sediment. Downstream, upwelling water forms a wedge of buffered temperatures. Hyporheic exchange associated with LWD does not significantly impact diel surface water temperatures. I tested these fluid and heat flow relationships in a second-order stream in Valles Caldera National Preserve (NM). Log additions created alternating zones of upwelling and downwelling in a reach that was previously losing throughout. By clearing LWD from channels, humans have reduced hydrologic connectivity at the meter-scale and contributed to degradation of benthic and hyporheic habitats. Dams also significantly alter hydrologic connectivity in modern rivers. Continuous water table measurements show that 15 km downstream of the Longhorn dam (Austin, Texas), river stage fluctuations of almost 1 m induce a large, unsteady hyporheic exchange zone within the bank. Dam-induced hyporheic exchange may impact thermal and geochemical budgets for regulated rivers. Together, these three case studies broaden our understanding of complex drivers of hyporheic exchange in small, natural streams as well as large, regulated rivers.Item Compressibility and permeability of Gulf of Mexico mudrocks, resedimented and in-situ(2014-05) Betts, William Salter; Flemings, Peter Barry, 1960-Uniaxial consolidation tests of resedimented mudrocks from the offshore Gulf of Mexico reveal compression and permeability behavior that is in many ways similar to those of intact core specimens and field measurements. Porosity (n) of the resedimented mudrock also falls between field porosity estimates obtained from sonic and bulk density well logs at comparable effective stresses. Laboratory-prepared mudrocks are used as testing analogs because accurate in-situ measurements and intact cores are difficult to obtain. However, few direct comparisons between laboratory-prepared mudrocks, field behavior, and intact core behavior have been made. In this thesis, I compare permeability and compressibility of laboratory-prepared specimens from Gulf of Mexico material to intact core and field analysis of this material. I resediment high plasticity silty claystone obtained from Plio-Pleistocene-aged mudrocks in the Eugene Island Block 330 oilfield, offshore Louisiana, and characterize its compression and permeability behavior through constant rate of strain consolidation tests. The resedimented mudrocks decrease in void ratio (e) from 1.4 (61% porosity) at 100 kPa of effective stress to 0.34 (26% porosity) at 20.4 MPa. I model the compression behavior using a power function between specific volume (v=1+e) and effective stress ([sigma]'v): v=1.85[sigma]'v-⁰̇¹⁰⁸. Vertical permeability (k) decreases from 2.5·10-¹⁶ m² to 4.5·10-²⁰ m² over this range, and I model the permeability as a log-linear function of porosity (n): log₁₀ k=10.83n - 23.21. Field porosity estimates are calculated from well logs using two approaches; an empirical correlation based on sonic velocities, and a calculation using the bulk density. Porosity of the resedimented mudrock falls above the sonic-derived porosity and below the density porosity at all effective stresses. Measurements on intact core specimens display similar compression and permeability behavior to the resedimented specimens. Similar compression behavior is also observed in Ursa Basin mudrocks. Based on these similarities, resedimented Gulf of Mexico mudrock is a reasonable analog for field behavior.Item Core-scale heterogeneity and dual-permeability pore structure in the Barnett Shale(2014-12) Cronin, Michael Brett; Flemings, Peter Barry, 1960-I present a stratigraphically layered dual-permeability model composed of thin, alternating, high (~9.2 x 10⁻²⁰ m²) and low (~3.0 x 10⁻²² m²) permeability layers to explain pressure dissipation observed during pulse-decay permeability testing on an intact Barnett Shale core. I combine both layer parallel and layer perpendicular measurements to estimate layer permeability and layer porosity. Micro-computed x-ray tomography and scanning electron microscopy confirm the presence of alternating cm-scale layers of silty-claystone and organic-rich claystone. I interpret that the silty-claystone has a permeability of 9.2 x 10⁻²⁰ m² (92 NanoDarcies) and a porosity of 1.4% and that the organic-rich claystone has a permeability of 3.0 x 10⁻²² m² (0.3 NanoDarcies) and a porosity of 14%. A layered architecture explains the horizontal (k [subscript H] = 107 x 10⁻²¹ m²) to vertical (k [subscript V] = 2.3 x 10⁻²¹ m²) permeability anisotropy ratio observed in the Barnett Shale. These core-scale results suggest that spacing between high-permeability carrier beds can influence resource recovery in shales at the reservoir-scale. I also illustrate the characteristic pulse-decay behavior of core samples with multiple mutually-orthogonal fracture planes, ranging from a single planar fracture to the Warren and Root (1963) "sugar cube" model with three mutually-orthogonal fracture sets. By relating sub core-scale matrix heterogeneity to core-scale gas transport, this work is a step towards upscaling experimental permeability results to describe in-situ gas flow through matrix at the reservoir scale.Item Dependence of transport properties on grain size distribution(2016-12) Tripp, Brandon Jamal; Daigle, HughThe topic of this thesis is investigating the relationship between grain size distribution and absolute permeability for medium silt to very fine-grained sandstones that are typical reservoir rocks in deepwater, offshore environments. I analyzed the relationship between grain size, mean grain size, median grain size, and grain size mode; grain size standard deviation; and absolute permeability through the amalgamation of numerical modeling and experimental core data for marine clay from the Pacific Ocean and Gulf of Alaska. The Pacific Ocean core sample was selected to represent porous media exhibiting narrow grain size distributions; the Gulf of Alaska samples were selected to represent porous media exhibiting broad grain size distributions. I constructed porous media composed of random packings of spheres with grain size distributions modeled on the grain size distribution of the Pacific Ocean core, and determined permeability by performing Lattice-Boltzmann simulations. The narrow grain size distributions exhibited a power law relationship between grain size standard deviation and permeability relationship. I then compared these results to measured data on the Gulf of Alaska samples, which exhibited very broad grain size distributions. The Gulf of Alaska samples had a different relationship between permeability and the standard deviation of the grain size distribution, although the relationship was still a power law. This illustrates how the breadth of the grain size distribution must be considered in empirical permeability relationships.Item Determination of the Controls on Permeability and Transport in Shale by Use of Percolation Models(2012-10-19) Chapman, IanA proper understanding of reservoir connectivity is essential to understanding the relationship between the porosity and the permeability within it. Additionally, the construction of an accurate reservoir model cannot be accomplished without this information. While a great deal is known about the connectivity in conventional sandstone systems, little is understood about the connectivity and its resultant properties within shale systems. Percolation theory is a method to describe the global properties of the shale system by understanding the nanometer scale interaction of pore space. In this study we use both analytical and empirical techniques to further understand shale pore scale interactions as well as global phenomena of the shale system. Construction of pore scale connectivity simulations on lattice and in the continuum allow for understanding relationships between pore topology, system porosity and system permeability. Additionally, questions regarding the role of Total Organic Carbon as well as natural fractures in contributing to shale permeability will be discussed. Analytical techniques are used to validate simulation results regarding the onset of percolation and related pore topology. Finally, time of flight simulation is used to further understand pressure transient behavior in the resulting topological models. High aspect ratio pores are shown to be the driver of shale permeability as opposed to the low aspect ratio pore space associated with organic matrix. Additionally, systems below the percolation threshold are likely able to produce because the wellbore will often encounter near infinite clusters. Finally, a characteristic volume growth profile is shown for a multi-porosity system whereby each level of porosity displays a corresponding stair step of volume growth in time.Item Effect of network structure modifications on the light gas transport properties of cross-linked poly(ethylene oxide) membranes(2009-05) Kusuma, Victor Armanda; Freeman, B. D. (Benny D.); Yacamán, M. JoséCross-linked poly(ethylene oxide) (XLPEO) based on poly(ethylene glycol) diacrylate (PEGDA) is an amorphous rubbery material with potential applications for carbon dioxide removal from mixtures with light gases such as methane, hydrogen, oxygen and nitrogen. Changing the polymer network structure of XLPEO through copolymerization has previously been shown to influence gas transport properties, which correlated with fractional free volume according to the Cohen-Turnbull model. This project explores strategic modifications of the cross-linked polymer structure and their effect on the chemical, physical and gas transport properties with an aim to develop rational, molecular-based design rules for tailoring separation performance. Experimental results from calorimetric and dynamic thermal analysis studies are presented, along with pure gas permeability and solubility obtained at 35°C. Incorporation of dangling side chains by copolymerization of PEGDA with methoxy-terminated poly(ethylene glycol) methyl ether acrylate, n=8 (PEGMEA) was previously shown to be effective in increasing fractional free volume of XLPEO through the opening of local free volume elements, which in turn increased CO₂ permeability. Through a comparative study ofshort chain analogs to these co-monomers, incorporation of an ethoxy-terminated co-monomer was shown to be more effective than a comparable methoxy-terminated co-monomer in increasing gas permeability. For instance, copolymerization of PEGDA with 71 wt% ethoxy-terminated diethylene glycol ethyl ether acrylate increased CO₂ permeability from 110 barrer to 320 barrer. Gas permeability increase was not observed when hydroxy or phenoxy-terminated pendants were introduced, which was attributed to reduction in chain mobility due to increased inter-chain chemical interactions or steric restrictions, respectively. Based on these results, incorporation of a co-monomer containing a bulky non-polar terminal group, tris-(trimethylsiloxy)silyl, was examined in order to further increase gas permeability. Addition of 80 wt% TRIS-A co-monomer increased CO₂ permeability of cross-linked PEGDA to 800 barrer. However, the resulting changes in chemical character of the copolymer reduced CO₂/light gas selectivity, even as gas permeability increased. The effect of incorporating a bulky, stiff functional group in the cross-linker chain was studied using cross-linked bisphenol-A ethoxylate diacrylate, which showed 40% increase in permeability compared to cross-linked PEGDA. This study affirmed the importance of polymer chain interaction, in addition to free volume, in determining the gas transport properties of the polymer.Item Effect of pressure-dependent permeability on tight gas wells(Texas A&M University, 2005-08-29) Franquet Barbara, MarielaTight gas reservoirs are those reservoirs where the matrix has a low permeability range (k < 0.1 md). The literature documents laboratory experiments under restressed conditions that show stress dependent rock properties are more significant in tighter rocks. For gas reservoirs, real gas properties are also sensitive to variations of pressure, and the correct description of gas flow must include pressure-dependent gas properties. Under these circumstances the resulting equation for real gas flow is a second order, non-linear, partial differential equation. Non-linearities include pressure-dependence of gas viscosity, gas compressibility, reservoir permeability and reservoir porosity. This paper investigates dynamic permeability change as a function of net overburden stress in tight gas reservoirs. The gas reservoir simulator used for this work included pressure-dependent reservoir permeability. Radial flow cases are analyzed using this simulator. During this study we found that from analysis of production data alone, it is impossible to determine the correct permeability value for tight gas reservoirs with pressure-dependent permeability. For the cases studied, the transient performance was similar for both constant permeability and pressure-dependent permeability. This similarity causes constant permeability and pressure-dependent permeability to be indistinguishable, based on analysis of transient performance data. It was found that the productivity index decreases when pressure-dependent permeability is more significant. Finally, this study verified that the method of Ibrahim et al.28 under estimates original gas in place (OGIP) for tight gas reservoirs with pressure-dependent permeability.Item Effect of rough fractal pore-solid interface on single-phase permeability in random fractal porous media(2016-08) Cousins, Timothy Alexander; Daigle, Hugh; Prodanović, MašaSingle-phase permeability k has intensively been investigated over the past several decades by means of experiments, theories and simulations. Although the effect of surface roughness on fluid flow and permeability in single pores and fractures as well as in a network of fractures was studied previously, its influence on permeability in a random mass fractal porous medium constructed of pores of different sizes remained as an open question. A fractal medium is one whose pore space and solid matrix can be characterized by statistical self-similarity and described by a fractal dimension Dm. Specifically, in a random mass fractal, each iteration of construction of the medium is composed of identical-size particles and pores of different sizes that are distributed randomly within (Hunt et al. 2014). This thesis contains the research into the effect of rough pore-solid interface on single-phase flow and permeability in fractal porous media. Using fractal geometry, randomly generated three-dimensional Menger sponges were created to model porous media with a range of mass fractal dimensionalities Dm between 2.579 and 2.893. This dimensionality characterizes both the solid matrix and the pore space of the media. The pore-solid interface of the media is subsequently roughened using the Weierstrass-Mandelbrot approach and controlled primarily by the surface fractal dimension Ds and root-mean-square of roughness height σ. The permeability was calculated for all the roughened media using the lattice-Boltzmann method using D3Q19 geometry and Bhatnagar-Gross-Krook (BGK) collision model. The LBM simulations calculated the single-phase permeability based on Darcy’s Law. Results indicate that permeability decreases sharply with increasing Ds from 1 to 1.1 regardless of Dm value, and remains relatively constant as Ds increases from 1.1 to 1.6. Furthermore, while creating the media, a lower bound for the percolation threshold appeared to be around 29.8% for randomized Menger sponges. When fitted to the percolation model presented in Larson et al. (1981) with an upper limit of 0.36 from Kim et al. (2011), the parameters from a least squares fit point to a critical porosity ϕc of 30% and a percolation exponent t between 3.1 and 3.3. Future research should investigate the effect of the percolation threshold for these simulated porous media and the effect surface roughness would have on this threshold. Finally, future research should expand into two-phase flow and investigate the effects of surface roughness on relative permeability and capillary pressure in simulated fractal porous media.Item Energy Dissipation Properties of Cementitious Materials: Applications in Mechanical Damping and Characterization of Permeability and Moisture State(2012-10-19) Leung, ChinThe study of mechanical energy and electrical energy dissipation in cementitious materials can lead to development of high damping concrete for structural applications, and new non-destructive testing techniques for use on existing concrete structures. This research aims to improve mechanical damping properties of cementitious materials and determine durability parameters from complex permittivity measurements. Damping was improved by utilizing poromechanical effects, and by adding viscoelastic and nanometric inclusions. Poromechanics was utilized to model and predict damping on specimens designed to maximize poromechanical effects, and composite theory was used to predict composite bounds for the loss tangent, i.e. modeling the effects on damping due to the addition of viscoelastic inclusions. Experimental results indicated that substantial damping improvement can be realized by both poromechanical effects and adding novel inclusions into cement pastes. The models were able to predict experimentally measured damping as a function of loading frequency. The electrical energy dissipation in cementitious materials was studied by dielectric spectroscopy as a function of moisture state and pore structure/permeability. The results were compared to predictions from multiphase composite modeling, where the properties of the confined water was inversely determined and used to predict moisture content. It was found that moisture state of cementitious materials has a linear relation to the complex permittivity over a wide variety of frequency ranges. Composite model prediction indicated that permeability of saturated cementitious materials studied in this research is likely dependent on the amount of free water in the pores. Permeability can be inferred from the pore structure of the cement paste via complex permittivity measurements by conditioning cement paste at different levels of relative humidity.Item Evaluation of transport and transport stability in glassy polymer membranes(2014-05) Czenkusch, Katrina Marie; Paul, Donald R.; Freeman, B. D. (Benny D.); Sanchez, Isaac C; Ellison, Christopher J; Li, WeiBoth novel membrane materials with better separation characteristics and a better fundamental understanding of membrane transport stability are needed to improve the competitiveness of commercial membrane separations. In this work, the effect of a novel moiety, hexafluoroalcohol, on the gas transport properties of an aromatic polyimide membrane are evaluated. The hexafluoroalcohol group increases the membrane’s fractional free volume, which increases the membrane’s permeability to all gases. Additionally, the HFA-containing polyimide shows resistance to plasticization by carbon dioxide. However, ideal selectivity for several gas pairs is unchanged by the inclusion of hexafluoroalcohol and the increase in the polymer’s fractional free volume. This lack of selectivity loss with increasing free volume is attributed to hydrogen bonding between the hexafluoroalcohol and imide groups, which reduces chain mobility. The ethanol dehydration characteristics of a so-called “TR” polymer are also evaluated in this work. TR polymers are heterocyclic, aromatic polymers synthesized by a solid-state, high temperature condensation from ortho-functional polyimides. Pervaporation studies on a representative TR polymer film demonstrate that the material has separation properties that exceed those of a commercial ethanol dehydration membrane. The transport properties of the TR film, combined with high thermal and chemical stability characteristic of these materials, make TR polymers promising materials for high-temperature, high-water content ethanol dehydration. Finally, the physical aging and plasticization of cellulose triacetate, the dominant natural gas purification membrane, is presented. Although this material has been used industrially for over 30 years, the physical aging and plasticization of the material, particularly in sub-micron films, has never been studied. Although cellulose triacetate does show physical aging behavior, as observed by permeability decreases over time, cellulose triacetate thin films do not show accelerated aging. Furthermore, the plasticization of thin cellulose triacetate films is reduced, rather than increased as seen in other polymers. The unusual transport stability of thin cellulose triacetate films may be due to their complex, semi-crystalline morphology, which, due to the thermal instability of the material, may not be thermally controlled.Item Fracture and permeability analysis of the Santana Tuff, Trans-Pecos Texas(1990-12) Fuller, Carla Matherne; Sharp, John Malcolm, 1944-A fracture and permeability analysis was performed on the Santana Tuff because of its similarity to the Topopah Springs unit at the Yucca Mountain site. The Topopah Springs unit is the proposed horizon for the spent nuclear fuel repository. Because of the impossibility of completely characterizing the flow properties of the unit without destroying the characteristics that make it desirable as a repository, other ash flow tuffs must be studied. The Santana Tuff and the Topopah Springs tuff both are rhyolitic in composition, nonwelded to densely welded and fractured. Fractures were examined at six outcrop locations spanning a five mile area. Stereonets and rose diagrams were constructed from over 312 fracture orientations. Although the composite data showed two major orientations of nearly vertical fractures, fracture trends at individual outcrops showed a variety of preferred orientations. Over 900 surface permeability measurements were taken using a mini-permeameter. The samples were categorized by three observed types of surface weathering: fresh, weathered, or varnished. Fracture surfaces were generally classified as weathered. The average permeabilities for the samples are 55.33 millidarcies, 5.03 millidarcies, and 3.31 millidarcies, respectively. The one-way statistical analysis performed on the data indicated that the permeability of fresh tuff surfaces is significantly different than both the permeabilities of the weathered and varnished tuffs, using both a least significant difference and greatest significant difference test. However, no difference was shown to exist between the weathered and varnished tuff permeabilities. Samples of fresh, weathered, and varnished tuffs were examined by X-Ray Defraction, the Scanning Electron Microscope, and in thin section. The SEM analysis showed surface differences between the three weathering classifications. The weathered and varnished samples were similar, exhibiting a platy, lamellate texture. The fresh surfaces were irregular and jagged. In thin section, a thin rind of dark minerals (FE-oxides) is observed on the edges of the varnished samples and in microcracks. This fills surface pores and causes the reduction in permeability. Two other zones of weathering have been identified in some of the samples, which may also cause changes in permeability. Tuff permeabilities were also analyzed for directional dependence. After an ash flow tuff is deposited and cooled, it may undergo flattening of pumice fragments and glass shards. These flattened fragments can be identified in handsamples, and are indicative of the direction of flow emplacement. The analysis showed that permeability is enhanced parallel to the emplacement direction, which is generally horizontal. Cut surfaces showed a 30% decrease in permeability perpendicular to flow direction. On varnished surfaces, this trend is still evident, although decreased in magnitude. This is expected because of the clay particles which make up the desert varnish. This study indicates that the formation of low permeability weathering rinds in association with vertical fractures may inhibit infiltration at the surface. It may accelerate infiltration at depth and allow more fluid to penetrate vertically into the tuff. In the event that fluid is absorbed into the matrix, it will travel horizontally, along the enhanced permeability parallel to the emplacement direction.Item Gas flow through shale(2012-08) Sakhaee-Pour, Ahmad; Bryant, Steven L.The growing demand for energy provides an incentive to pursue unconventional resources. Among these resources, tight gas and shale gas reservoirs have gained significant momentum because recent advances in technology allowed us to produce them at an economical rate. More importantly, they seem likely to contain a significant volume of hydrocarbon. There are, however, many questions concerning hydrocarbon production from these unconventional resources. For instance, in tight gas sandstone, we observe a significant variability in the producibilities of wells in the same field. The heterogeneity is even present in a single well with changes in depth. It is not clear what controls this heterogeneity. In shale gas, the pore connectivity inside the void space is not well explored and hence, a representative pore model is not available. Further, the effects of an adsorbed layer of gas and gas slippage on shale permeability are poorly understood. These effects play a crucial role in assigning a realistic permeability for shale in-situ from a laboratory measurement. In the laboratory, in contrast to in-situ, the core sample lacks the adsorbed layer because the permeability measurements are typically conducted at small pore pressures. Moreover, the gas slippages in laboratory and in-situ conditions are not identical. The present study seeks to investigate these discrepancies. Drainage and imbibition are sensitive to pore connectivity and unconventional gas transport is strongly affected by the connectivity. Hence, there is a strong interest in modeling mercury intrusion capillary pressure (MICP) test because it provides valuable information regarding the pore connectivity. In tight gas sandstone, the main objective of this research is to find a relationship between the estimated ultimate recovery (EUR) and the petrophysical properties measured by drainage/imbibition tests (mercury intrusion, withdrawal, and porous plate) and by resistivity analyses. As a measure of gas likely to be trapped in the matrix during production---and hence a proxy for EUR---we use the ratio of residual mercury saturation after mercury withdrawal (S[subscript gr]) to initial mercury saturation (S[subscript gi]), which is the saturation at the start of withdrawal. Crucially, a multiscale pore-level model is required to explain mercury intrusion capillary pressure measurements in these rocks. The multiscale model comprises a conventional network model and a tree-like pore structure (an acyclic network) that mimic the intergranular (macroporosity) and intragranular (microporosity) void spaces, respectively. Applying the multiscale model to porous plate data, we classify the pore spaces of rocks into macro-dominant, intermediate, and micro-dominant. These classes have progressively less drainage/imbibition hysteresis, which leads to the prediction that significantly more hydrocarbon is recoverable from microporosity than macroporosity. Available field data (production logs) corroborate the higher producibility of the microporosity. The recovery of hydrocarbon from micro-dominant pore structure is superior despite its inferior initial production (IP). Thus, a reservoir or a region in which the fraction of microporosity varies spatially may show only a weak correlation between IP and EUR. In shale gas, we analyze the pore structure of the matrix using mercury intrusion data to provide a more realistic model of pore connectivity. In the present study, we propose two pore models: dead-end pores and Nooks and Crannies. In the first model, the void space consists of many dead-end pores with circular pore throats. The second model supposes that the void space contains pore throats with large aspect ratios that are connected through the rock. We analyze both the scanning electron microscope (SEM) images of the shale and the effect of confining stress on the pore size distribution obtained from the mercury intrusion test to decide which pore model is representative of the in-situ condition. We conclude that the dead-end pores model is more representative. In addition, we study the effects of adsorbed layers of CH₄ and of gas slippage in pore walls on the flow behavior in individual conduits of simple geometry and in networks of such conduits. The network is based on the SEM image and drainage experiment in shale. To represent the effect of adsorbed gas, the effective size of each throat in the network depends on the pressure. The hydraulic conductance of each throat is determined based on the Knudsen number (Kn) criterion. The results indicate that laboratory measurements made with N₂ at ambient temperature and 5-MPa pressure, which is typical for the transient pulse decay method, overestimate the gas permeability in the early life of production by a factor of 4. This ratio increases if the measurement is run at ambient conditions because the low pressure enhances the slippage and reduces the thickness of the adsorbed layer. Moreover, the permeability increases nonlinearly as the in-situ pressure decreases during production. This effect contributes to mitigating the decline in production rates of shale gas wells. Laboratory data available in the literature for methane permeability at pressures below 7 MPa agree with model predictions of the effect of pressure.Item Geomechanical aspects of fracture growth in a poroelastic, chemically reactive environment(2013-08) Ji, Li, active 2013; Olson, Jon E.; Balhoff, Matthew T.Natural hydraulic fractures (NHFs) are fractures whose growths are driven by fluid loading. The fluid flow properties of the host rock have a primary, but hitherto little appreciated control on the NHF propagation rates. This study focuses on investigating the impacts of host rock fluid flow on the propagation and pattern development of multiple NHF in a poroelastic media. A realistic geomechanical model is developed to combine both the fluid flow and mechanical interactions between multiple fractures. The natural hydraulic fracture propagation is observed to consist of a series of crack-seal processes indicating incremental stop-start growth. Growth timing is on the scale of millions of years based on recent natural fracture growth reconstructions. These time scales are compatible with some model scenarios. My newly developed numerical model captures the crack-seal process for multiple NHF propagation. A sensitivity study conducted to investigate the impacts of different fluid flow properties on NHF propagation shows that permeability is a predominate influence on the timescale of NHF development. In low-permeability rocks, fractures have more stable initiation and much longer propagation timing compared to those in high-permeability rocks. Another aspect of great interest is the influence of fluid flow on fracture spacing and pattern development for multiple NHFs propagation in a poroelastic environment. My new poroelastic geomechanial model combines the natural hydraulic fracturing mechanism with the mechanical interactions between fractures. The numerical results show that as host rock permeability decreases, more fractures can propagate and a much smaller spacing is reached for a given fracture set. The low permeability slows down the propagation of long fractures and prevents them from dominating the fracture pattern. As a result, more fractures are able to grow at a similar speed and a more closely spaced fracture pattern is achieved for either regularly spaced or randomly distributed multiple fractures in low-permeability rocks. Investigation is also conducted in analyzing the distributions of fracture attributes (length, aperture and spacing) in low- and high-permeability rocks. For shales with high subcritical index, low permeability helps the fractures propagate more closely spaced instead of clustering. Meanwhile, in low-permeability rocks, factures have relatively smaller apertures, which lead to a slower fracture opening rate. The competition between the slow fracture opening rate and quartz precipitation rate will affect the effective permeability and porosity of the naturally fractured reservoir. However, the competition is trivial in high-permeability rocks. Other factors, such as reservoir boundary condition, layer thickness, subcritical index and pattern development stage, all have considerable impact on fracture pattern development and attribute distribution in a poroelastic media.Item Geophysical investigations in the Nankai Trough and Sumatran subduction zones(2011-12) Martin, Kylara Margaret; Gulick, Sean P. S.The 2004 Sumatra-Andaman and the 2011 Tohoku-Oki earthquakes demonstrate the importance of understanding subduction zone earthquakes and the faults that produce them. Faults that produce earthquakes and/or tsunamis in these systems include plate boundary megathrusts, splay faults (out of sequence thrusts), and strike-slip faults from strain partitioning. Offshore Japan, IODP Exp. 314 collected logging while drilling (LWD) data across several seismically-imaged fault splays in the Nankai Trough accretionary prism. I combine LWD resistivity data with a model of fluid invasion to compare the permeabilities of sands. My results indicate that sands within faulted zones are 2-3 orders of magnitude more permeable than similar undisturbed sands. Therefore fault zones are likely to be fluid conduits within the accretionary wedge. Fluids can affect the physical and chemical properties of the faulted material, increasing pore pressures and effectively lubricating the faults. Fluids play an important role in fault slip, but hazard analysis also requires an understanding of fault geometry and slip direction. Both Japan and Sumatra exhibit strain partitioning, where oblique convergence between tectonic plates is partitioned between the megathrust and strike-slip faults proximal to the arc. Offshore Sumatra, I combine profiles from a 2D seismic survey (SUMUT) with previous bathymetry and active seismic surveys to characterize the West Andaman Fault adjacent to the Aceh forearc Basin. Along this fault I interpret transpressional flower structures that cut older thrust faults. These flower structures indicate that the modern West Andaman Fault is a right lateral strike-slip fault and thus helps to accommodate the translational component of strain in this highly oblique subduction zone. Offshore the Kii Peninsula, Japan, I analyze a trench-parallel depression that forms a notch in the seafloor just landward of the megasplay fault system, along the seaward edge of the forearc Kumano Basin. Using a 12 km wide, 3D seismic volume, I observe vertical faults and faults which dip toward the central axis of the depression, forming apparent flower structures. The along-strike geometry of the vertical faults makes predominantly normal or thrust motion unlikely. I conclude, therefore, that this linear depression is the bathymetric expression of a transtensional fault system. While the obliquity of convergence in the Nankai Trough is small (~15 degrees), this Kumano Basin Edge Fault Zone could be due to partitioning of the plate convergent strain. The location of the West Andaman Fault and KBEFZ within the forearc may be controlled by the rheology contrast between active accretionary wedges and the more stable crust beneath forearc basins.Item Head Loss Through Fibrous Debris Bed with Different Types of Perforated Strainers(2014-05-03) Abdulsattar, Suhaeb SSafety related issues in Nuclear Power Plants (NPPs) have always been of concern, especially those issues that are related to Light Water Reactors (LWRs) and their Design Basis Accidents (DBA). One of the ongoing issues that has been extensively studied is the Generic Safety Issue GSI-191, which is dedicated to study and resolve the issues that arise after a Loss-Of-Coolant-Accident (LOCA). Fibrous debris produced during the blow-down phase of Loss-of-Coolant Accidents is transported into the sump and becomes an important cause of head loss through the sump strainer, affecting the Emergency Core Cooling System (ECCS) performance. This study was dedicated to measure the pressure drop across randomly accumulated debris bed on the sump strainer along with measuring the debris bed thickness. Two different types of strainers were installed vertically, one at a time, in a horizontal flow loop and the debris bed thickness was measured during the bed build up process and after reaching steady state. Fifteen tests were conducted to determine the head loss difference between the two strainers and to study the characteristics of the debris bed accumulated on each strainer. The results from this experimental study were compared based on the approaching velocity, debris bed thickness, and strainer type. A realistic permeability model for the NUKON fiber glass insulation material was suggested, to be utilized in related applications, the suggested head loss model was compared to other head loss models developed in previous studies. The permeability model was developed from experimental data acquired from approaching velocities in the viscous region. There was no significant head loss difference between the two strainers for the minimum and intermediate range. Based on the experimental data, the head loss difference between the two strainers for the maximum range was about four times higher than the calculated head loss. The flow rate measurement uncertainty was main reason for the difference in the maximum range. There is a probability that the debris bypass could be different between the two strainers, thus, a debris bypass study is required to further investigate this difference.Item Hollow cylinder dynamic pressurization and radial flow through permeability tests for cementitous materials(2009-05-15) Jones, Christopher AndrewSaturated permeability is likely a good method for characterizing the susceptibility of portland cement concrete to various forms of degradation; although no widely accepted test exists to measure this property. The hollow cylinder dynamic pressurization test is a potential solution for measuring concrete permeability. The hollow cylinder dynamic pressurization (HDP) test is compared with the radial flow through (RFT) test and the solid cylinder dynamic pressurization (SDP) test to assess the accuracy and reliability of the HDP test. The three test methods, mentioned above, were used to measure the permeability of Vycor glass and portland cement paste and the results of the HDP test were compared with the results from the SDP and RFT tests. When the HDP and RFT test results were compared, the measured difference between the mean values of the two tests was 40% for Vycor glass and 47% for cement paste. When the HDP and SDP tests results were compared, the measured difference with Vycor glass was 53%. The cement paste permeability values could not be compared in the same manner since they were tested at various ages to show the time dependency of permeability in cement paste. The results suggest good correlation between the HDP test and both the SDP and RFT tests. Furthermore, good repeatability was shown with low coefficients of variation in all test permutations. Both of these factors suggest that the new HDP test is a valid tool for measuring the permeability of concrete materials.
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