CO2 Sequestration effect on outburst in coal mining

Coal mass has the potential to store substantial amounts of CO2 in the coal matrix and that CO2 has the ability to move through the coal seam pore and fracture systems, which influences the release of gases during coal mining and the CO2 sequestration process. In addition, the reduction of coal mass strength due to CO2 adsorption greatly affects the outburst process. The sudden and violent failure of coal seam with releasing large amount of gas is called outburst in coal mining. Up to date only few have been conducted to investigate the effect of CO2 adsorption induces strength reduction on the outburst process. The main objective of this study is to investigate the effect of CO2 injection on outburst in coal mining. Uniaxial Compressive Strength (UCS) experiments were therefore conducted on black coal samples, which have been saturated with CO2 and N2 at various pressures at 33 ºC. According to the results CO2 adsorption causes the UCS strength of coal to be reduced by up to 53 % and this higher strength reduction is due to the CO2 adsorption induce coal matrix swelling. However, N2 saturation causes the coal strength to be slightly increased. According to these observations, there is a high risk associated with CO2 sequestration process in coal seam as it significantly reduces the coal seam strength, which has direct influence on outburst process in coal

Geopolymer as well cement and variation of its mechanical properties under different curing temperature and curing mediums

Geo sequestration of carbon dioxide (CO2) has been found to be one of the best solutions to reduce anthropogenic amount of greenhouse gases to the environment. Well integrity of sequestration wells should be maintained for the success of any sequestration projects. Well cement plays a vital role in well integrity for any sequestration projects, and ordinary Portland cement (OPC) based well cement has been used in underground wells. There are many problems, such as cement degradation, chemical attacks, durability issues, leakage, etc., associated with OPC based well cement. One of the best replacements for OPC based well cement would be the use of geopolymer cement, as it is economical in production, sustainable in reducing waste products, consumes less energy, doesn‟t undergo chemical attacks, durable, resistive in acidic environments and possess higher strength compared to OPC. This paper will review suitability of geopolymer as well cement under downhole conditions, and analyse the advantages of using geopolymer over OPC-based well cement. Moreover, well cement will be exposed to range of temperatures, pressures and fluid medium from the ground surface to sequestration depths of more than 1 km. Therefore, this paper aims to study the mechanical behaviour of geopolymer under different curing temperatures (from 23 ºC to 80 ºC) and curing mediums (brine, water and CO2 saturated brine). It has been found that optimum curing temperature for higher strength is 60 ºC and geopolymer exhibits high strength compared to class G cement above ambient temperature. In addition, water saturated samples showed higher strength reduction compared to brine saturated geopolymer samples

Development of a 3d model to study the co2 sequestration Process in deep unmineable coal seams.

This paper presents a numerical model to study the carbon dioxide (CO2) sequestration process in deep coal seams and to investigate the factors that affect this process. A coal seam lying 1000 m below the ground surface was considered for the simulation. One injecting well was first inserted at the middle of the area under consideration and CO2 was injected for a 10 year period. With one injection well, the storage capacity was calculated as 13´107 m3. The number of injecting wells was then increased to 4. It was found that the maximum storage capacity was observed at two well conditions (an increment of 130% of the single well condition). However, further increasing the number of wells (up to 4) reduced the storage capacity to 12.5´107 m3. According to the model results, it is clear that CO2 storage capacity in deep unmineable coal seams is dependent on the number of injecting wells and their location and porosity, the permeability of the coal seams, coal bed moisture content and temperature

The mechanical behaviour of coal with respect to CO2 sequestration in deep coal seams

Carbon dioxide displays a strong affinity for coal due to its propensity to adsorb to the coal surface. The process of CO2 adsorption on coal causes lowering of surface energy and, it is hypothesised that an associated decrease in surface film confinement results in a decrease in material tensile resistance. Following the results of work carried out on the mechanical influence of CO2 on brown coal under in situ conditions [Viete DR, Ranjith PG. The effect of CO2 on the geomechanical and permeability behaviour of brown coal: implications for coal seam CO2 sequestration. Int J Coal Geol 2006;66(3):204-16], a theoretical explanation is proposed for the perceived lack of a weakening effect with the adsorption of CO2 to coal at significant confining pressures. We propose that at significant hydrostatic stresses, resistance to failure is otherwise provided (by external confinement) and the effects of adsorptive weakening are concealed. Our model predicts that adsorptive weakening, fracturing under in situ stresses, and associated permeability increases are not an issue for coal seam CO2 sequestration for sufficiently deep target seams. Lowering of the elastic modulus of coal upon introduction of CO2 may proceed by means other than surface energy lowering and could well occur irrespective of the depth of sequestration. The effect of elastic modulus lowering under in situ conditions would be beneficial for the long-term retention of sequestered gases

A study of rock abrasivity and tool wear in Coal Measures Rocks

This paper examines the relations between Cerchar abrasivity index (CAI) and petrographic properties of Coal Measures Rocks in the Zonguldak Coal Basin, Turkey. In this study, petrographic properties and abrasivity indices of 29 sedimentary rock samples were determined and the values of CAI and petrographic analysis results were compared. A good linear relationship between CAI and average quartz grain size parameters was found. The test results also showed that abrasivity was affected by the mineralogical composition, cement type, degree of cementation, quartz content, and average quartz grain size. It was found that abrasivity of rock was decreased by the low grade of cementation between abrasive minerals. CAI values and petrographic properties were used to estimate tool consumption in underground works in the Zonguldak Coal Basin. It was observed that when CAI values increased, tool consumption increased. © 2007 Elsevier B.V. All rights reserved.Fundamental Research Fund of Shandong University: 2002-45-03-19The authors thank Zonguldak Karaelmas University Research Fund (Project No: 2002-45-03-19) and the Department of Mining Engineering of Zonguldak Karaelmas and Çukurova Universities for their contributions in producing this study

Use of Digital Terrestrial Photogrammetry in rocky slope stability analysis by Distinct Elements Numerical Methods

Current approaches to rocky slope stability analysis require knowledge of the geometrical-structural setting, as well as the physical-mechanical properties of the intact material and its discontinuities. The physical-mechanical properties are derived from in situ and laboratory tests, while the geometrical characteristics come from field attitude measurements. Frequently, the inaccessibility of walls does not allow direct measurement of discontinuity surfaces by traditional geological methods. In such cases, data can only be obtained by statistical methods. Although this approach is significant and provides spatial meaning, it is ineffective for deterministic analysis. This paper provides a solution to this problem by applying digital terrestrial photogrammetric techniques employing a reamed bar, an aerostatic balloon and a helicopter. Results demonstrate that the accuracy and the quantity of geometrical and engineering-geological data coming from the photogrammetric survey, allow for numerical simulation of the relationship between rock elements as a function of their physical-mechanical properties and load conditions. The 3DEC code was chosen among the different methods available to model the discontinuous media through distinct elements. The proposed methodology was applied to a quarry located in the Carrara Marble District (the Apuan Alps, Italy), the largest and most exploited mining region in Europe. The economic value of the area required a detailed study of the presence of instability phenomena so that marble extraction could continue in safe conditions

Influence of rock mass properties on blasting efficiency

The purpose of this paper is to determine the influence of rock mass properties on the blasting efficiency which is ratio of the block size distribution of the rock mass to the block size distribution of the muck-pile. The proposed methodology of blasting efficiency in this study is to compare physical and mechanical properties of the rock mass and block fragmentation under the same blasting conditions in Ki{dotless}rka borax mine. Intact rock properties, block size of rock mass before blasting and muck pile after blasting were found to measure blasting efficiency. Firstly, intact rock properties, which are unit volume weight, water absorption, uniaxial compressive strength, tensile (Brazilian) strength, cohesion and internal friction angle, were tested for each mining bench. Secondly, block sizes of rock masses in respect to discontinuity boundaries were measured and muck pile photos were taken in order to determine Block Fragmentation (BF) which is to separate the rock mass block size by blasting and that of the corresponding muck pile. Thirdly, statistical analysis between rock mass properties and block fragmentation were developed and these analysis test results have shown that a good relation between block fragmentation and Brazilian tensile strength and internal friction angle were found. As a result, block fragmentation in the same blasting conditions and other rock properties can be estimated from the best empirical correlations with the rock properties. © 2009 Academic Journals

Stress versus strain behaviour of geopolymer cement under triaxial stress conditions cured in saline and normal water

Geopolymer cement was evaluated as wellbore sealing material for carbon dioxide geosequestration application. Curing of cement system in saline water and strength testing in triaxial stress state condition under lateral confinement is relevant to primary cementing in CO2 geosequestration wellbore in saline aquifer. Geopolymer cement was cured in saline water (both at ambient conditions for 28 days and heated (60°C) conditions for 12 hours) and tested for triaxial strength at different levels of lateral confinement. Normal water and few other curing techniques were also studied both for geopolymer and API ‘G’ cement. Results reported were compared to evaluate the suitability of saline water for curing of geopolymer cement. Unconfined compression test results showed higher strength for curing in saline water than normal water. Besides, testing strength under lateral confinement demonstrated the material failure behavior from brittle to plastic

Simulation of mixed-mode fracture using SPH particles with an embedded fracture process zone

This paper focuses on the modelling of mixed‐mode fracture using the conventional smoothed particle hydrodynamics (SPH) method and a mixed‐mode cohesive fracture law embedded in the particles. The combination of conventional SPH and a mixed‐mode cohesive model allows capturing fracture and separation under various loading conditions efficiently. The key advantage of this framework is its capability to represent complex fracture geometries by a set of cracked SPH particles, each of which can possess its own mixed‐mode cohesive fracture with arbitrary orientations. Therefore, this can naturally capture complex fracture patterns without any predefined fracture topologies. Because a characteristic length scale related to the size of the fracture process zone is incorporated in the constitutive formulation, the proposed approach is independent from the spatial discretisation of the computational domain (or mesh independent). Furthermore, the anisotropic fracture responses of materials can be naturally captured thanks to the orientation of the fracture process zone embedded at the particle level. The performance of the proposed approach demonstrates its potentials in modelling mixed‐mode fracture of rocks and similar quasi‐brittle materials.Yingnan Wang, Hieu T. Tran, Giang D. Nguyen, Pathegama G. Ranjith, Ha H. Bu