Infiltration of highly concentrated solutions into unsaturated sand is suspected to be affected by the liquid-gas interfacial tension between the resident water and that of the infiltrating solution. The wetting of non-porous solid surfaces by liquids is commonly quantified by contact angle measurements. However, it is well known that wettability of porous solids cannot be accurately obtained by optical inspection because the liquid is penetrating into the pores of the solid in question. The main objective of this investigation was to find an effective method to measure contact angle in coarse porous media such as sandy soils. In this study, we compare both static and dynamic methods to estimate the contact angle formed by solutions of varying surface tension on silica sands. In addition, the contact angle of the imbibing solutions is estimated in both dry and water-wetted sand. Experiments in this study employed three clear acrylic columns of known volume to determine contact angles using two methods, one static method and one dynamic method. The three acrylic columns were packed with the same mass of each grade of Accusand�� (40/50, 30/40, 20/30, and 12/20 grades respectively) for triplicate measurements. The solutions used in this study included (1) pure water and (2) 5 molal NaNO��� and (3) n-hexane as a reference. The static method estimated contact angles in initially dry sand of 23�� for 40/50 sand, and 30�� to 33�� for 12/20, 20/30, and 30/40 sands, with the same values obtained for both solutions. Contact angles of these solutions observed in the dynamic test, were twice those found in the static test (averaging 45�� and 62�� respectively). In the case of pre-wetted sands, dynamic imbibition with water provided an estimated contact angle of 2��, while the NaNO��� solution yielded 21�� contact. Based on relative surface tensions of water and the 5 molal NaNO���, the Young's equation predicts a contact angle of 25��. These results strongly support recent claims of effective contact angles between these miscible, but contracting, fluids. The observed data suggest that the zero contact angle assumption is a poor one even for clean dry silica sand. In a dynamic system, gravitational forces cannot be ignored in course porous media. An analytical method, used to model imbibition of the solutions into the silica sands, was both accurate and useful for estimating contact angle. / Graduation date: 2002

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

A robust understanding and planning of production enhancement and flow assurance is required as petroleum E&P activities are targeting deepwaters and long distances. Different flow assurance issues and their solutions are put together in this work. The use of multiphase pumps as a flow assurance solution is emphasized. Multiphase pumping aids flow assurance in different ways. However, the problem causing most concern is sand erosion. This work involved a detection-based sand monitoring method. Our objectives are to investigate the reliability of an acoustic sand detector and analyze the feasibility of gel injection as a method to mitigate sand erosion. Use of a sand detector coupled with twin-screw pumps is studied under varying flow conditions. The feasibility of gel injection to reduce slip and transport produced solids through twin-screw pump is investigated. A unique full-scale laboratory with multiphase pumps was utilized to carry out the experimental tests. The test results indicate that acoustic sand detection works in a narrow window around the calibration signature. An empirical correlation for predicting the twin-screw pump performance with viscous fluids was developed. It shows good agreement in the practical operational limits – 50% to 100% speed. The results indicate that viscous gel injection should be an effective erosion mitigation approach as it reduces slip, the principle cause of erosive wear. To correlate the performance of viscous fluid injection to hydroabrasive wear, further experimental investigation is needed.

Particle shape is evaluated on three scales corresponding to form, roundness and roughness. Shape at each of these scales uniquely influences material behavior. The shape of sand grains is largely formed as magma cools. Subsequent cleavage and abrasion change the roundness and roughness of particles. Published results indicate that particle shape influences several aspects of granular systems behavior including stiffness, strength, the evolution of strength anisotropy, dilation, and the development of strain localization. The crushing of granite creates a particulate material with a unique angular shape. A wide range of experimental studies implemented as part of this research permit assembling a unique database of material parameters and comparing the behavior of several crushed and natural sands. In general, the low roundness of crushed sands leads to higher maximum void ratios, lower small strain stiffnesses, and higher critical state friction angles than more rounded natural sands. It also impacts mortar strength and workability. Previous studies have emphasized size-controlled segregation. New experimental results show that differences in particle shape can also lead to segregation in a binary granular material. Round or spherical particles are more mobile than angular or flat particles. Then, the greater motion of round or spherical particles in a binary mixture subjected to horizontal or vertical vibration results in their segregation from their angular or flat neighbors. Particle shape may change significantly with stress in the case of soft particles. Therefore, the presence of shape-deformable particles decreases the stiffness of binary rigid-soft particle mixtures. However, macro-scale measurements with rigid-soft mixtures show higher stiffness than would be expected by volume averaging techniques. A subsequent microscale study shows the formation of backbone chains made of the rigid particles, partially supported by the soft particles which prevent the buckling of the load-carrying chains.

A robust understanding and planning of production enhancement and flow assurance is required as petroleum E&P activities are targeting deepwaters and long distances. Different flow assurance issues and their solutions are put together in this work. The use of multiphase pumps as a flow assurance solution is emphasized. Multiphase pumping aids flow assurance in different ways. However, the problem causing most concern is sand erosion. This work involved a detection-based sand monitoring method. Our objectives are to investigate the reliability of an acoustic sand detector and analyze the feasibility of gel injection as a method to mitigate sand erosion. Use of a sand detector coupled with twin-screw pumps is studied under varying flow conditions. The feasibility of gel injection to reduce slip and transport produced solids through twin-screw pump is investigated. A unique full-scale laboratory with multiphase pumps was utilized to carry out the experimental tests. The test results indicate that acoustic sand detection works in a narrow window around the calibration signature. An empirical correlation for predicting the twin-screw pump performance with viscous fluids was developed. It shows good agreement in the practical operational limits – 50% to 100% speed. The results indicate that viscous gel injection should be an effective erosion mitigation approach as it reduces slip, the principle cause of erosive wear. To correlate the performance of viscous fluid injection to hydroabrasive wear, further experimental investigation is needed.

Asphalt bound mixtures have been put to diverse uses. The complicated nature of the material and the demanding conditions under which it is used preclude complete solutions to questions on load bearing capability under field conditions. In proportion to the quantity of its usage and in acknowledgment of modeling complexity, the material has been interrogated by many researchers using a variety of mechanical tests, and a plethora of linear viscoelastic models have been developed. Most models are intended to account for specific classes of problems. This work addresses the conspicuous absence of systematic documentation of normal forces generated as a result of shear. The normal force generated during simple shear is a clear indication of the nonlinear nature of the material. The effect of fillers (hydrated lime and limestone), air voids, aggregate gradation, asphalt source and step loading on normal force generation during torsion is experimentally investigated. Based on experimental evidence, a non-linear thermomechanical model for sandasphalt mixtures based on the idea of multiple natural configurations is developed. The model accounts for the fact that the mixture has a natural configuration (stressfree configuration) which evolves as it is subjected to loads. Assumptions are made regarding the manner in which the material stores and dissipates energy. A key assumption is that among the various constitutive relations possible, the one that is chosen is the one that maximizes the rate of entropy production. The model that is developed accounts for the anisotropic nature of the response. The experimental results show that asphalt bound mixtures generate significant normal forces even at low rotation rates. The source of asphalt, aggregate gradation, fillers and air voids have a pronounced effect on normal stress generation. The model is corroborated against data from torsion experiments.

Among many useful properties of elastomers, one is their ability to absorb energy by deforming to large strains without fracturing. This property combined with their good adhesion to substrates makes them suited as adhesive films and coatings for protection against impact damage. An example of practical significance is the erosion of helicopter rotor blades where the protection of leading edge is often achieved by mounting a film or applying a coat of polyurethane. Although this is a workable solution, there is currently little knowledge as to the durability of this elastomeric film/coat under impact of hard and angular particles such as sand. A deformation and failure analysis that deals with the angularity of the erodents and captures the local mechanisms responsible for erosion damage in elastomers is the sine qua non. The present endeavor tries to address these issues by considering a polyurethane layer on a quasi-rigid substrate, impacted by hard particles at velocities and angles of attack given by pre-specified distributions. A novel method is devised to address the angularity issue. A series of finite-element calculations are performed on the coating layer-substrate systems subjected to different velocities, incidence and angularity of the impacting erodents. An elasto-plastic material constitution with isotropic hardening is employed in the simulations and material parameters representative of polyurethane are used for the coat. Initial parametric deformation analyses provided an adequate qualitative estimate of erosion parameters. Incorporation of a stress based fracture criterion enabled a quantitative measure of material removal due to erosion to be achieved. The simulation results show good match with experimental trends of target mass loss as obtained under normal and inclined loadings with angular erodents. The current simulation framework has sufficient capability and versatility to incorporate more enriched polymer-models and advanced fracture criteria in the future, thereby allowing parametric studies toward selection of materials and coat-layer thicknesses thus predicting the erosion mass loss as accurately as measured by experiments.

The production of sand can be a major issue in many young, unconsolidated sandstone formations where there is little to no cement holding the individual sand grains together. When such reservoirs are produced, quite often operators face problems with reduced well productivity and equipment failure. Because of these issues, the industry has developed numerous techniques in its effort to control formation sand production. Sand consolidation is one technology that has been studied and used since the 1940s. The theory behind sand consolidation technology is to place a liquid material which will create a grain to grain contact that will bind individual sand grains together. Most consolidation treatments contain a preflush to clean and wet the surface, the consolidating system to bind the sand grains and give residual strength, and, finally, an overflush to ensure the formation is still able to produce fluids. With the successful placement of this fluid, the sand grains will be locked in placed so that they will not be produced. The technology has gone through many phases of conception since the 1940s; however, most consolidation material that is pumped in the past has been based upon an epoxy or furan backbone. While there are many technologies available, for the purpose of my research, the epoxy technology was experimentally investigated. The testing of the fluid involved investigating numerous additives to obtain the correct residual strength of the sample, as well as the necessary retained permeability. For the epoxy fluid, the optimal preflush, epoxy system and overflush formulations were determined after 250 checkout tests. Based upon these tests, the fluid was optimized to its working time and UCS results. The optimal system included the addition of PA2 to the preflush, along with PA1 and an aromatic amine curing agent to the epoxy system. PA1 and PA2 are adhesion promoter additives which were deemed necessary as a result of the testing. This system was then tested further in a HP/HT cell. While there is still room for improvement with respect to retained permeability, the system still performs very well in terms of UCS.

An experimental study was conducted to verify experimentally whether sand consolidation by high-temperature alkaline treatment was possible in the heavy oil Bachaquero-01 reservoir. The experiments were conducted using sand samples from a core taken from well LL-231 from Bachaquero-01 reservoir. The sample was placed in a vertical 18 in. long aluminum cylindrical cell with an ID of 1.5 in. The top half of the cell was thermally insulated and the bottom half was cooled. The alkaline treatment (pH 11 -12) at 230ºC - 250ºC and 900 – 1000 psig was injected at 20 ml/min for 3 to 6 hours at the top of the cell and liquid produced at the bottom of the cell. After each experiment, the cell contents were removed and analyzed to determine if consolidation occurred. An electron microprobe was used to analyze both loose and polished epoxy-mounted sand grains to determine any change in texture and composition of the sand pack and precipitation and growth of secondary phases. Results showed that under the experimental conditions reached in the laboratory; the consolidation of Bachaquero-01 sand did not occur. However some secondary materials were produced in the runs where sand samples were cleaned of oil. It was noticed that the amount of these secondary phases was not sufficient to bridge the sand grains. These results indicate that further research is needed to better understand and optimize the parameters affecting the consolidation of Bachaquero-01 sands.

The static cone penetration tests are quite extensively used for carrying out in-situ geotechnical investigations both for onshore and offshore sites especially where the soil mass is expected to comprise of either soft to medium stiff clays or loose to medium dense sands. The wide use of the cone penetration tests (CPT) in geotechnical engineering has resulted in a great demand for developing necessary correlations between the cone penetration resistance and different engineering properties of soils. The successful interpretation of the cone penetration test data depends mainly on the various empirical correlations which are often derived with the help of a controlled testing in calibration chambers. The calibration chambers have been deployed in various sizes (diameter varying from 0.55 m to 2.10 m) by a number of researchers. It is quite an expensive and time consuming exercise to carry out controlled tests in a large size calibration chamber. The task becomes even much more difficult when a sample comprising of either silt or clay has to be prepared. As a result, most of the reported cone penetration tests in calibration chambers are mainly performed in a sandy material. Taking into account the various difficulties associated with performing tests in large calibration chambers, in the present study, it is attempted to make use of a miniature static cone penetrometer having a diameter of 19.5 mm. This cone was gradually penetrated at a uniform rate in a triaxial cell in which a soil sample of a given material was prepared; the diameter of the cone was intentionally chosen smaller so that the ratio of the diameter of the cell to that of the cone becomes a little larger. Two different diameters of the cells, namely, 91 mm and 140 mm, were used to explore the effect of the ratio of chamber (cell) size to that of the cone size. In addition, the rate of penetration rate was also varied from 0.6 mm/minute to 6.0 mm/minute (the maximum possible rate for the chosen triaxial machine with the larger cell) to examine the effect of the rate of the penetration of the miniature cone on the tip resistance. By using the chosen experimental setup, a large number of static miniature cone penetrometer tests were carried out on four different materials, namely, (i) clean sand, (ii) sand with 15% silt, (iii) sand with 25% silt, and (iv) sand with 15% fly ash. The cone tip resistance for each material was obtained for a wide range of three different relative densities. The effective vertical pressure (σv) for the tests on different samples was varied in between 100 kPa and 300 kPa. The variations of the tip resistance with axial deformation in all the cases were monitored so as to find the magnitude of the ultimate tip resistance. In contrast to the standard cone, the diameter of the piston shaft was intentionally kept a little smaller than that of the cone itself so as to restrict the development of the piston resistance. For each cell (chamber) size, two different sizes of the pistons were used to assess the resistance offered by the penetration of the piston shaft itself. It was noted that the resistance offered by the chosen piston shaft is not very substantial as compared to that of the cone tip itself. Most of the experimental observations noted from the present experiments were similar to those made by the penetration of the standard size cone in a large calibration chamber. The ultimate tip resistance of the cone was found to increase invariably with an increase in the magnitude of σv. An increase in the relative density of the soil mass leads to an increase in the value of qcu. For the same range of relative densities, an addition of fly ash in the sample of sand, leads to a considerable reduction in the magnitude of qcu. Even with the addition of 25% silt, the values of qcu were found to become generally lower as compared to clean sand and sand added with 15% silt. An employment of a larger ratio of the diameter of the cell to that of the miniature cone leads to an increased magnitude of qcu. An increase in the penetration rate from 0.6 mm/min to 6.0 mm/min, was found to cause a little increase in the magnitude of qcu especially for sand added with fly ash and silt. The effect of the penetration rate on the results was found to increase continuously with a reduction in the rate of penetration. At higher penetration rates, in a range closer to those normally employed in the field (20 mm/sec), it is expected that the rate of penetration of the cone will not have any substantial effects on the magnitude of qcu for clean sands. The magnitude of qcu obtained in this thesis at different values of σv for all the cases with the use of the miniature cone were compared with the two widely used correlations in literature. It is found that except for dense sands, in most of the cases, the present experimental data lie generally in between the two correlation curves from literature; for dense sands the measured values of qcu were found to be significantly lower than the chosen correlation curves. It was noted that with the use of the miniature cone penetrated in a given sample prepared in a triaxial cell, it is possible to obtain reasonably an accurate estimate of the tip resistance of the standard cone especially for loose to medium dense states of all the materials. Further, from the analysis of all the tests results, it was noted that approximately a linear correlation between qcu/σv and soil friction angle (φ) for different chosen materials exists provided the dependency of the φ on the stress level is taken into account. As compared to the standard cone penetrometer which is usually employed in the field, the miniature cone used in this study is expected to provide a little conservative estimate, of the tip resistance of the standard static cone penetrometer with reference to the different materials used in this study on account of the facts that (i) there is a reduced area behind the cone, (ii) the ratio of the diameter of the calibration chamber (cell) to that of cone is not very high, (iii) the chosen size of the cone is smaller than the standard cone, and (iv) the chosen penetration rate is much smaller than the standard rate of penetration. Further, in the case of clean sand, an attempt has also been made in this thesis, with the help of a number of direct shear tests at different stress levels, to generate an expression correlating peak friction angle, critical state friction angle, relative density of sand and vertical effective stress. A correlation has been generated with the help of which, the value of peak dilatancy angle can be obtained from the known values of peak friction angle and critical state friction angle. In confirmation with the available information in literature, this exercise on clean sand has clearly indicated that a decrease in the magnitude of vertical effective stress leads to an increase in the values of both peak friction angles and peak dilatancy angles.