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Collaborating Authors
Drilling Fluids and Materials
Abstract This paper is aimed to confirm the possibility to excavate fractured rock masses by using EPB shields, even in presence of relevant water tables. This verification is based on laboratory test experiences carried out at TUSC laboratory of Politecnico di Torino, where the natural material is tested in order to verify the suitability of a certain conditioning technique in particular conditions. This is due to the fact that every case should be studied apart from existing studies on a certain rock type, as other factors such as fragmentation of the rock mass, natural water content and porosity of the rock can considerably influence the final result of the conditioning process. The most important aspects that allow to consider the conditioning of fractured rock masses as suitable are: possibility to create a plastic paste that can transmit the pressure at the front in a effective way; reduce the permeability of the spoil material in order to reduce the possibility of water leakage inside the chamber and eventually in the tunnel; verify the consistency of the conditioned material for the extraction through the screw conveyors and the belt conveyors. For this research an argillitic schistose rock mass, with some quartzitic and calcareous inclusions, has been studied by using different level of conditioning in order to verify the suitability of an eventual EPB excavation through this formation. Introduction EPB shield technology is widely used in soil excavation, especially in urban areas, because of its effectiveness to control surface settlements and to carry out the work in safe conditions. The safety is increased if we consider the fact that the front can be stabilized by using the earth pressure generated in the excavation chamber. Moreover with this method also the presence of water, both in saturated media and as seepage force, can be easily handled reducing risks for the manpower. For these reasons, several underground projects are realized by using this technology. The improvement of the machines and conditioned processes allowed to extend the scope of application of EPB machines from soils to rock masses. This possibility is given thanks to the use of tools able to disaggregate the rock into small chips (few centimeters wide) that, together with finer material coming from the excavation process, can create suitable mix for the conditioning with foaming agents. More fractured is the initial excavation face, better is usually the result, as the finer material represents the biggest part in the size distribution of the spoil material which enter in the chamber and also the foam can penetrate deeper in the excavation face.
- Well Drilling > Drilling Fluids and Materials > Drilling fluid management & disposal (0.57)
- Reservoir Description and Dynamics > Reservoir Characterization (0.37)
Abstract In this work, we found that contact between shale and water results in development of micro fractures. Based on results of experiments on Pierre shale, we conclude that appearance of micro fractures begin with saturation of capillaries, ionic and diffusive transport of water into the shale clays and once capillaries are saturated, the cause of micro fracture propagation is the conversion of ionic activity/exchange to excess pressure that did not exist before fracking. Based on these findings, the spread of micro fractures appear to be a time-dependent phenomenon which has not been addressed in the existing macro/micro fracture models. Introduction Shale has often been involved as a hazard in drilling operations. This hazard can be defined as "destabilization" of shale. When contacted with water-based drilling fluids, some shales readily swell and sometimes, cause the wellbore to cave-in, slough, wash-out, close, and pack-off, impeding the drilling by sticking the drill-pipe. However, once drilling reaches the desired depth or length, the casing is set, cemented, and perforated, and then actually we wish to initiate fractures and destabilize the shale formation, using hydraulic fracturing. Clays constitute a major portion of minerals in shale. These clays contain a large amount of free energy which is the main factor for "slick" water adsorption/absorption. In fact, the reason for using "surfactants" in hydraulic fracturing fluids is to make the penetration of the fluid into the capillaries much easier, thus water meets with less resistance to enter the small capillaries. Also, the result of high capillary suction pressure is due to small Angstrom size capillaries, smaller pores and presence of ions and hydrateable metal atoms. The free energy is thus, related to all the above mentioned and other affects. Capillary pressure, osmotic pressure and other pressures are responsible for creating the micro-fractures in shale, thus, increasing the network of micro-fractures which leads to more gas production. The objective of this study is to evaluate the pressures of the individual ions which are released by the diffusing "slick" water into shale. These pressures would be added to the above mentioned capillary pressure, osmotic pressure, bacterially-induced pressures, chemically-induced reaction pressure, pressure due to exchangeable ion-transport, pressure due to release of free energy of solvation and eventually to the pore pressure as suggested by Terzaghi's equation.
- North America > United States > Louisiana (0.30)
- North America > Canada (0.19)
- Well Completion > Hydraulic Fracturing (1.00)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid management & disposal (0.54)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.51)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.48)
An Investigation into the Effect of Mixing Time and Pulp Density on the Mechanical Propreties of Sodium Silicate Fortified Cementd Hydrulic Back Fill, Gelfill
Kermani, M. (McGill University) | Hassani, F. (McGill University) | Aflaki, E. (Amirkabir University of Technology) | Benzaazoua, M. (Université du Québec en Abitibi Témiscamingue) | Nokken, M. (Concordia University)
Abstract This paper presents and compares the physical properties of Gelfill and cemented hydraulic fill (CHF) obtained by lab experiments. Gelfill consists of tailings, different binders such as Portland cement, fly ash and blast furnace slag and an alkali activator such as sodium silicate. The CHF and Gelfill samples with various mixture designs were cast and cured for 28 days. The influence of sodium silicate concentration, pulp density and mixing time on the mechanical properties of samples were evaluated using the uniaxial strength test. Mercury intrusion porosimetery (MIP) was used to analyse the microstructure of CHF and Gelfill samples. This study concludes that:The mechanical properties of CHF can be improved by the addition of appropriate amount of sodium silicate. The rate of strength acquisition in Gelfill samples is faster than CHF samples over 28 days of curing period. Mixing time strongly influences the mechanical properties of Gelfill samples but did not have any effect on CHF samples. The MIP analyses indicate that the pore size distribution and total porosity of Gelfill and CHF were different, and this did contribute to higher strength development of the Gelfill samples. Introduction The increased depths of mines in the Canadian Shield and the high stress associated with these depths favour a new method of mine backfill that can both meet strength requirements and help mine productivity. The mine backfill mainly consists of tailings, water and binder materials, the latter being most expensive. Gelfill is a new mine backfill material whose binder usually consists of alkali activators such as sodium silicate and other cementitious materials such as blast furnace slag and normal Portland cement. Although sodium silicate has been used in concrete manufacture, the use of this material in mine backfill is relatively new (Doucet, 2007, Razavi, 2007). Until very recently there have been only a few isolated publications, mostly out of McGill University, regarding mine Gelfill (Razavi, 2007 and Kermani et al., 2009 and 2010). These papers have investigated some of the basic mechanical properties and mechanical behaviour of Gelfill. However, the physical performance of Gelfill in various conditions has yet to be understood. Therefore, the main objective of this study was to investigate the influence of mixing time and sodium silicate concentration on the mechanical performance of Gelfill and CHF through a series of experiments. Moreover, the microstructure of the Gelfill and CHF samples was studied.
- Research Report > New Finding (0.68)
- Research Report > Experimental Study (0.54)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
Evaluation of 3-D Strain Distribution in Lignite Based on Image Analysis
Fukuda, D. (Hokkaido University) | Maruyama, M. (Hokkaido University) | Aramaki, N. (Horonobe RISE) | Kaneko, K. (Horonobe RISE) | Nara, Y. (Tottori University) | Kodama, J. (Hokkaido University) | Fujii, Y. (Hokkaido University)
Abstract Evaluation of three dimensionally non-uniform strain distribution in rocks under various conditions such as in water or under freeze-thaw cycles is of significant importance to understand their complex deformations and fracturing mechanisms. For this purpose, we developed an image analysis method which can evaluate or "measure" the three dimensional (3-D) strain distribution in rocks. The proposed method utilizes the 3-D images of rock under initial and deformed configurations, which are obtained by some imaging techniques such as X-ray computed tomography (X-ray CT). In the proposed method, the obtained 3-D images are divided into multiple sub-regions of interest. For each sub-region, the strain is evaluated utilizing 3-D affine transform with unknown coefficients to be determined. In the first step, 3-D voxel level displacements at multiple representative points in each sub-region are computed by 3-D digital volume correlation technique between the comparison images and the initial-guess of the transform coefficients are obtained. In the second step, referring to the initial-guess of unknown transform coefficient, they were optimized in sub-voxel level by finding optimum digital volume correlation between the comparison images, which can evaluate the transform coefficients with higher precision. From the calculated transform coefficients, the strain was directly obtained through the spatial derivative of displacement based on affine transform. In this paper, along with the description of the proposed method, the evaluation of deformation in a lignite specimen due to immersion in water was presented as an application example. As the 3-D imaging technique, micro-focus X-ray CT was applied. The result showed that the induced dilatational strain field due to the initiation and extension of cracks in the specimen was clearly captured. Therefore, authors believe that the proposed method can be applicable to various problems in rock mechanics. Introduction It is of significant importance to understand fracture mechanisms in various rocks for geological and engineering problems which require such as the assessment of long-term integrity of subsurface rock structures excavated in a rock mass. It is now widely accepted that rock fracturing involves with nucleation and propagation of micro cracks from pre-existing heterogeneities, which can be in the form of pores, cracks, inclusions or other defects (e.g., Wong et al., 2001). To date, systematic, theoretical and experimental investigations of initiation, propagation and coalescence of cracks in brittle solids including rocks have been conducted and it has been shown that the fracturing is a process from the proliferation and coalescences of micro cracks to the formation of the main fracture due to locally induced stress concentration or strain localization (e.g., Ortiz, 1988). However, the application of ordinary mechanical testing apparatus for such as uni- (or multi-)axial tests with displacement meters or strain gages mounted on the specimen surface cannot clarify the phenomena occurring inside of the rock specimen during the test. Thus, although it is still possible to obtain many insights from the aforementioned tests, the discussion tends to be largely conjectural and it is often the cases that the surface imaging techniques are applied to the post-fractured specimen and the "fracturing process" cannot be discussed. To solve the above difficulty, non-destructive imaging techniques such as X-ray computed tomography (X-ray CT) and magnetic resonance imaging (MRI) have been found to be one of the most attractive tools and have been applied to the investigation of deformation and fracturing in rocks under various types of loading and environmental conditions (e.g., Lenoir et al., 2007; Kodama et al., 2011; Marica et al. 2006).
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics (1.00)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (0.65)
- Data Science & Engineering Analytics > Information Management and Systems > Artificial intelligence (0.65)
Abstract Cohesive fracture is a mechanical model widely used for modeling quasi-brittle fracture in rocklike materials. This work discusses use of this model to simulate quasi-brittle fractures generated by injection stimulation during the process of cuttings reinjection in West Africa. Cuttings reinjection is an engineering practice used for disposal of drilling waste. During this process, hydraulic fractures are created at the target formation and milled cuttings are injected with fluid. In practice, this process must remain in compliance with environmental regulations and zero-discharge policies. The purpose of this study is to determine the following factors of injection design for a field in West Africa:pumping pressure capacity required to successfully perform the injection and the injection rate for injection performance and the value of fracture width under injection. A simplified three-dimensional (3D) finite element model (FEM) was built. A poroelastic plastic damage model was used for simulation of the cohesive crack prorogation within the target formation. For simplicity, fracture development in both horizontal and vertical directions was simulated separately. In this way, the computational burden for one calculation was reduced to a reasonably low level, without losing accuracy of the model. Loads of the model include fluid injection and gravity, which balances the initial geostress field. Various values of injection rate were used in these calculations to determine the most reasonable value of injection pressure. The capacity of pressure of a pumping device was determined using this optimized value of injection pressure. Results in values of width and length of fractures created by the injection are presented. Injection pressures at bottom-hole (BHP) corresponding to each value of injection rate are also given. Numerical results for fracture generation and propagation in a horizontal direction were visualized. The pumping pressure capacity required to fulfill the cuttings reinjection work was determined based on the numerical results of optimized injection rates and pressure. The fracture width was determined using the given pumping pressure. The length and height of the fractures was determined using pumping pressure along with the required volume of cuttings waste to be disposed of into the formation. This work presents a case study of 3D finite element modeling of hydraulic fracturing generated by cuttings reinjection. The results of the optimized injection rate and pressure provide a best practice and a useful reference for cuttings reinjection analyses in this region.
- Africa > West Africa (0.85)
- North America > United States > Texas (0.28)