Soundless Cracking Demolition Agents (SCDAs) are an alternative to the current practices of environmentally detrimental conventional demolition and rock fragmentation methods Although having the potential to produce a dense network of fractures when injected into a borehole, the applicability of SCDA is limited by its susceptibility to dilution in water-saturated conditions and delayed onset of expansive pressure. Such limitations can be eliminated by introducing a Viscousity Enhancing Agent (VEA) to modify the SCDA system. Even though adding a VEA enhances the wash out resistance in the SCDA system, the associated delay in the onset of expansive pressure limits the application of this new technology in the industry. Therefore, this study aims to recover the delayed onset of expansive pressure in modified SCDA by utilising a chemical accelerator (CaCl2) through a comprehensive experimental study. The developed new material was fully characterised by performing mechanical tests (uniaxial compressive strength tests, flowability tests, washout resistance tests), microstructural analysis (scanning electron microscopy) and mineralogical analysis (X-ray diffraction). According to the results, simply increasing the dose of CaCl2 in unmodified SCDA was found to be ineffective to attain an increased rate of expansive pressure generation and the peak expansive pressure development. The increased dose of CaCl2 resulted in an accelerated expansive pressure generation, but also a lower peak expansive pressure. The approach of combining the accelerator and VEA was found to be an effective means to increase the washout resistance and the rate of expansive pressure development of modified SCDA while retaining a reasonable flowability of SCDA. Finally, the study proposes an optimum combination of VEA (welan gum, 0.1%) and the accelerator (CaCl2, 2%) by weight of SCDA to produce an SCDA with enhanced expansive pressure generation in submerged conditions, which can be effectively and safely applied for demolition and rock fragmentation. Crown Copyright (C) 2018 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers. All rights reserved.

Because over 60% of the total energy consumed in conventional mining consists of excavating, hauling, and liberating processes, the energy consumption in conventional methods of mining has increased exponentially with the decline in global ore-grades. In-situ leaching (ISL) is an alternative mining technology, which eliminates these processes. However, ISL is currently limited to porous rock. Expansion of ISL to impervious mineral bearing rocks requires controlled, artificial fracture stimulation and the current practice of hydraulic fracturing is not compatible due to the associated environmental impacts and uncontrolled fracture propagation. Therefore, to extend the application of ISL to impervious rocks, an alternative fracturing method using Soundless Cracking Demolition Agents (SCDAs), which is capable of producing controlled fractures in a rock mass, is proposed in this study. With the aim of understanding the fracturing performance of SCDA under in-situ stress conditions prevalent in ISL environments, a 3D numerical model for SCDA charging was produced using Particle Flow Code (PFC3D 5.0) and validated with experimentally obtained data. The model was then extended to investigate the fracture mechanism of SCDA charging at various confining pressures of 5, 10, 15, and 20 MPa. Simulation results suggest that during SCDA charging, the number of radial fracture propagations and the total fracture damage in the rock mass increase with the confinement and the fracture pattern is dependent on the confining stress of the surrounding rock. In comparison to a hydraulically fractured specimen with identical dimensions, the fracture density of SCDA charged specimen showed a ten-fold increase at high confining pressures (20 MPa). Furthermore, as opposed to an uncontrolled, unidirectional diametrical fracture generated by hydraulic fracturing, SCDA charging produces multiple radial fractures around the injection well facilitating better spatial distribution of fluid flow for ISL. The results of this study imply that SCDA charging produces a denser and a controllable fracture network compared to hydraulic fracturing, which could potentially expand ISL applications to impervious rocks. Crown Copyright (C) 2018 Published by Elsevier Ltd. All rights reserved.

Alternative fragmentation technologies such as soundless cracking demolition agents (SCDAs) can minimize adverse environmental impacts associated with conventional rock fracturing methods used in mining and energy industries. However, application of SCDA in deep underground environments is limited due to (1) inability of SCDA to react in saturated rock masses as a result of dilution and mass washout effects, and (2) slow expansive pressure generation in SCDA, which delays post-fracturing operations. This study addresses the first issue by modifying a generic SCDA using a viscosity-enhancing admixture (VEA), namely welan gum, to produce a hydrophobic SCDA for direct application in submerged conditions. The effect of the VEA, on the mechanical, microstructural and mineralogical morphology of hydrating SCDA was also investigated. According to the findings, adding just 0.1% of VEA by weight to the SCDA in combination with a water-reducing admixture significantly improves the washout resistance without compromising the fluidity of SCDA, however, at the expense of rapid expansive pressure generation rates. The reduction in expansive pressure, which is unfavourable for mining and energy engineering applications is caused by the interaction of VEA with the hydrating SCDA. This is evident in the SEM and XRD results observed. This urges the consideration of both positive and negative effects of welan gum in SCDA: enhancement of washout resistance and reduction of expansive pressure development prior to any field application.

Fracture stimulation using soundless cracking demolition agents (SCDAs) is a potential alternative technique to induce high-density fractures in sedimentary reservoir-rock as an auxiliary technique to improve the efficiency of enhanced oil and gas recovery efficiencies. However, to date, its application has been limited to fracture stimulation in dry rock masses. Therefore, using modified SCDAs, which can be used for underwater rock fracturing, a series of experiments was conducted to investigate the fracturing performance of SCDAs in saturated rock masses. 18 coarse-grained sandstone specimens were saturated in water, oil, and NaCl brine and fractured using three different SCDA types: a standard SCDA (S1), and two modified for underwater application (S2) and accelerated reaction rate (S3). Then, the fractured samples were scanned in the Australian Synchrotron, and the fractures were quantified using Avizo 9.0.1. The fracture initiation time and the total fracture network length and volume were found to be dependent on the saturated pore fluid of rock. Water saturation of samples increased the fracture initiation time by 16.5%, 24.1% and 13.68% for S1, S2, and S3 type SCDAs respectively and reduced the fracturing potential of SCDA by 59.5%, 32.49% and 66.67% compared to dry samples. This reduction was less apparent in oil-saturated samples as the high pore fluid viscosity of oil-saturated samples aid fracturing, which is explained by the Poiseuille equation. Increasing salinity in the saturation fluid from 0% to 12.5% was favourable for the fracturing efficiency of SCDAs because of the formation of CaCl2 in the pore fluid, which accelerates the reaction of SCDA. Fracture orientation also changed depending on the saturation fluid, which was again governed by the variation in reaction rate in SCDAs under different saturation conditions.

The low permeability of gas hydrate deposits leads to poor extraction rates. Artificial fracture stimulation could significantly improve the recovery rate of an estimated 300 trillion m3 of this untapped future energy source, which form in seabed sedimentary deposits. Because conventional methods of rock fragmentation are inapplicable in such deposits due to sudden release of energy that may impose the risk of methane release to the atmosphere, alternative rock fragmentation technologies are necessary for artificial fracture stimulation of gas hydrate deposits. We checked the effectiveness of a new hydrophobic non-explosive demolition agent as a rock fracturing technique, which could potentially be used as a third-generation disruptive technology for mining (3G-DTM). Laboratory experiments performed by mimicking deep-sea environments suggest that the density of the gradually generated rock mass fractures increases with confining pressure and pore fluid salinity. Importantly, due to the fracturing nature of 3G-DTM, the fracture density can be significantly improved (by 116%) with increasing the confining pressure (from 70 kPa to 20 MPa). Increased salinity of the rock pore fluid also improved the fracture density by 38% at 20 MPa confining pressure when the salinity increased from 0% to 20%. Furthermore, the rock is subjected to a gradual fracturing process in the 3G-DTM fracturing (10–15 h in the laboratory experiments) allowing for a safer, more controlled fracture propagation, making 3G-DTM a substitute for conventional rock fragmentation in marine environments.

CO2 sequestration and enhanced coal bed methane (ECBM) extraction necessitate CO2 injection into coal reservoirs that affect the coal strength properties and long-term integrity of the seam. Evaluation of CO2-induced coal strength alterations is essential to minimize the reservoir damage. Advanced soft computing models have become prevalent in rock mechanics field, as they are capable of learning trends from complex data sets, preserving the experience and using it for predictions. We present two models viz. artificial neural network (ANN) and adoptive neuro-fuzzy inference system (ANFIS) to predict the strength alterations of coal, under various CO2 saturation conditions. Model performances are compared with linear and non-linear multivariate regression analyses (L-MRA and NL-MRA). We consider three effective input parameters (i.e. coal type, CO2 saturation pressure and CO2 interaction time) and one output parameter (i.e. unconfined compressive strength (UCS)) in the models. ANN consists of a three-layer feed-forward back-propagation network with a 3-5-1 architecture and ANFIS consists of [4 4 4] Gaussian type membership functions. Model results confirm that ANFIS has the highest prediction capacity followed by ANN, with R-2 equal to 0.9954 and 0.9933, respectively. Both L-MRA and NL-MRA prediction performances are not satisfactory, as R-2 values are only 0.7854 and 0.7821 for two models, respectively. Thus, general statistical models like MRA fail to precisely predict the complex strength alterations. From the verified models, we show that well-trained ANN and ANFIS models can successfully fit and forecast the experimental data, and are able to predict the long-term CO2 saturation effect on coal strength. Crown Copyright (C) 2018 Published by Elsevier Ltd. All rights reserved.

The carbon dioxide (CO2) adsorbed in coal seams during CO2-enhanced coal bed methane recovery (CO2-ECBM) causes substantial coal matrix alterations, resulting in significantly reduced flow performance. Many studies have been conducted to date on the effect of CO2 phase on coal mass permeability. However, the effect of coal rank on these permeability changes with CO2 phase has not yet been studied. Therefore, the main aim of this study is to investigate how the influence of CO2 phase condition on coal flow performance varies with rank. A series of tri–axial permeability tests was conducted using Australian brown coal samples for both CO2 and N2 under various confinements and injections at 35°C. The results were then compared with those for high-rank coal reported in the literature. According to the test results, greater coal macro-pore-structure rearrangement occurs with super-critical CO2 adsorption, resulting in lower permeability in coal, regardless of rank. However, this CO2 phase influence is much greater for high-rank coal. Although coal permeability reduces with depth for any rank of coal, this depth effect reduces with increasing rank. Furthermore, although N2 has the ability to recover CO2 adsorption-induced swelled areas in coal regardless of rank, that capability is much greater for high-rank coal.

Sand production during hydrocarbon production is a crucial problem in the petroleum industry. Although extensive research has been conducted in the past, there is a need to gain a better understanding of the sand production mechanisms from unconsolidated and weakly consolidated sand reservoirs, in order to develop a predictive model to quantify sand production. The main objective of this study is to examine factors influencing sand production from a screen. Such knowledge can be effectively used to minimise sand production in the field. First, a new sand production cell was designed and developed to study the sand production process. The cell constructed with a Perspex screen enables observation of the sand production process in real time through a slot simulating a wire wrapped screen or a slotted liner.The cell was then used to investigate the factors that affect sand production in unconsolidated sand formations, including the slot size, injecting gas pressure, sand particle size and moisture content. Experimental results show that sand production is highly dependent on slot size, sand particle size, moisture content and injection pressure. The rate of sand production increases with increasing injection pressure due to the increase in drag forces acting on sand formation, and excessive injection pressures may cause total collapse in sand formation. Moisture content shows a negative influence on sand production because the inter-molecular attraction between sand particles increases with increasing moisture content. These preliminary experimental results appear consistent with the findings of past research, which demonstrates that the developed cell can be effectively used to study the sand production process in geological formations. A sand production model was then developed as a function of gas injection pressure and moisture content, which can predict cumulative sand production quite accurately when the outlet is 3 mm in diameter and the mean sand particle size is between 600 mu m and 850 mu m. (C) 2013 Elsevier B.V. All rights reserved.

The characteristics of rock instability precursors and the principal stress direction are very crucial for the prevention of geological disasters. This study investigated the qualitative relationship between rock instability precursors and principal stress direction through wave velocity in rock acoustic emission (AE) experiments. Results show that the wave velocity variation exhibits obvious anisotropic characteristics in 0%–20% and 60%–90% of peak strength due to the differences of stress-induced microcrack types. The amplitude of wave velocity variation is related to the azimuth and position of wave propagation path, which indicates that the principal stress direction can be identified by the anisotropic characteristics of wave velocity variations. Furthermore, the experiments also demonstrate that the AE event rate and wave velocity show quiet and stable variations in the elastic stage of rock samples, while they present a trend of active and unstable variations in the plastic stage. It implies that both the AE event rate and wave velocity are effective monitoring parameters for rock instability. The anisotropic characteristics of the wave velocity variation and AE event rate are beneficial complements for identifying the rock instability precursors and determining the principal stress direction, which provides a new analysis method for stability monitoring in practical rock engineering.