Distribution Measurement and Mechanism Research on Deformation due to Losing Water of Overburden Layer

Abstract Based on FBG fiber Bragg grating technology and BOTDA distributed optical fiber sensing technology, this study used fine sand to simulate overburden layer in vertical shaft model equipment. The placing technique and test method for optical fiber sensors in the overburden layer were studied, combined with MODFLOW software to simulate the change of the water head value when the overburden layer was losing water, and obtained the deformation features of overburden layer. The results showed that at the beginning of water loss, the vertical deformation increased due to larger hydraulic pressure drop, while the deformation decreased gradually and tended to be stable with the hydraulic pressure drop reducing. The circumferential deformation was closely related to the distance between the drainage holes, variations of water head value and the method of drainage. The monitoring result based on optical fiber sensing technology was consistent to the characteristics of water loss in overburden layer simulated by MODFLOW software, which showed that the optical fiber sensing technology applied to monitor shaft overburden layer was feasible

Distributed fibre optic strain sensing of an axially deformed well model in the laboratory

Well integrity is crucial in enabling sustainable gas production from methane hydrate reservoirs and real-time distributed monitoring techniques can potentially facilitate proper and timely inspection of well integrity during gas production. In this research, the feasibility of distributed fibre optic strain monitoring with Brillouin optical time domain reflectometry/analysis (BOTDR/A) for well monitoring was examined by conducting a laboratory test on a well model subjected to axial tensile deformation, which occurs due to reservoir compaction during gas production. First, the validity of the proposed experimental methodology is assessed by a finite element analysis and theoretical modelling of a well subjected to reservoir compaction. A 3 m long well model is developed from the modelling and is instrumented with different types of fibre optic cables to measure the distributed strain development during tensile loading. Results show that the proposed well model and loading scheme can satisfactorily simulate the axial tensile deformation of the well in the laboratory condition. BOTDR is capable of capturing the tensile strain development of the well model accurately within the limitation of the spatial resolution of the BOTDR measurement. To enable accurate distributed strain monitoring of well deformation with BOTDR/A, the following issues are discussed: tightly buffered coating layers around optical fibre cores through mechanical compression and/or chemical adhesion, and a small number of coating layers

Fibre optic monitoring and finite element analysis of well integrity in methane hydrate reservoirs

Well integrity is crucial for sustainable hydrocarbon production from oil and gas reservoirs. The number of new wells can be minimized by maintaining the integrity of existing wells. Also, oil and gas leakage due to compromised well integrity can be curtailed through proactive well integrity management. The present research focuses on well integrity analysis and monitoring for methane hydrate reservoirs. Methane hydrate reservoirs are susceptible to large deformation due to their unconsolidated nature, which could substantially compromise well integrity during well construction as well as gas production periods. Therefore, in the present research, finite element analyses (FEA) and laboratory experiments of well integrity are carried out for the case of the Nankai Trough methane hydrate reservoir in Japan, in order to contribute to a better well integrity management. FEA on well construction and reservoir compaction processes as well as cement shrinkage process is conducted. Laboratory experiments are carried out with a distributed fibre optic monitoring technique called Brillouin optical time domain reflectometry/analysis (BOTDR/A) on the strain development of laboratory-scale well specimens subjected to tensile and bending loading. The primary contributions of the present research are as follows. First, cement shrinkage volumes for the Nankai Trough formation case are estimated to be up to 0.7%. Second, cement shrinkage of 0.7% during well construction induces stress concentrations in the high hydrate saturation layers of the Nankai Trough formation. Third, the well is found to become most vulnerable to damage in the initial stages of hydrate dissociation under large depressurisation. Forth, fibre optic cables with minimal number of coating layers and tight interlayer buffering will be effective for accurate in-well integrity monitoring with BOTDR/A. Fifth, fibre optic cables should be attached on the casing rather than in the cement in the well to facilitate accurate bending curvature monitoring with BOTDR/A

The Mechanical Behavior of Salt X

Rock salt formations have long been recognized as a valuable resource - not only for salt mining but for construction of oil and gas storage caverns and for isolation of radioactive and other hazardous wastes. Current interest is fast expanding towards construction and re-use of solution-mined caverns for storage of renewable energy in the form of hydrogen, compressed air and other gases. Evaluating the long term performance and safety of such systems demands an understanding of the coupled mechanical behavior and transport properties of salt. This volume presents a collection of 60 research papers defining the state-of-the-art in the field. Topics range from fundamental work on deformation mechanisms and damage of rock salt to compaction of engineered salt backfill. The latest constitutive models are applied in computational studies addressing the evolution and integrity of storage caverns, repositories, salt mines and entire salt formations, while field studies document ground truth at multiple scales. The volume is structured into seven themes: Microphysical processes and creep models Laboratory testing Geological isolation systems and geotechnical barriers Analytical and numerical modelling Monitoring and site-specific studies Cavern and borehole abandonment and integrity Energy storage in salt caverns The Mechanical Behavior of Salt X will appeal to graduate students, academics, engineers and professionals working in the fields of salt mechanics, salt mining and geological storage of energy and wastes, but also to researchers in rock physics in general

Development and Lab Calibration of the Pnuematic In-situ Soil Caving Index Sampler (PISCIS)

The caving/sloughing of sandy layers into drilled shafts is a common and costly phenomenon in the drilling industry. A prototype soil-testing device known as the Pneumatic In-situ Soil Caving Index Sampler (PISCIS) has been developed to test sandy layers above the water table for their propensity to cave/slough into a drilled shaft during the drilling process. The PISCIS fits down a Cone Penetration Test (CPT) hole and uses air pressure to agitate a sample off of the hole wall that is then collected and weighed. Large-scale lab testing was conducted using sand under a variety of simulated overburden pressures and fines contents. The tests were conducted with a dual purpose in mind. First, the tests confirmed the functionality of the PISCIS prototype and its ability to collect samples in a consistent and repeatable manner. Second, the tests resulted in a calibration curve that shows a very strong (nearly exponential) relationship between collected sample weight and the fines content of the test sand; higher fines contents resulted in lower collection weights. The PISCIS was designed to supplement information found in a geotechnical report with information that would specifically inform drilling contractors about potential caving/sloughing hazards found in the stratigraphy

Patterns of stress and strain distribution during deep mining at Boulby, N. Yorkshire

The understanding of stress-deformation state transmission within the rock mass above deep mine workings is a key factor to the comprehension of the response of rock masses to changes of stress regime brought about by the mining activity for the safety of surface and subsurface structures. Based on monitoring data from active actual mine workings, this study numerically analyzes factors controlling stress and deformation using the 2D Fast Lagrangian Analysis of Continua (FLAC 2D) code and a strain-softening model to approximate creep behaviour of rock masses. The results show that distribution of stress and deformation at Boulby mine is primarily governed by the lithological heterogeneity of the overlying strata and the geological structure, including its nature within the undermined area. Data from a bespoke roof-to-floor monitoring closuremeter indicate that convergence of openings is a function of local variables, including the site location, geometry and age of the site. Patterns of ground subsidence are compared to the pattern of levelling-based measured ground subsidence. Furthermore, the analysis shows that the strain-softening model reasonably approximates the creep behaviour of the excavations. The results have implications for how we monitor and model subsidence due to mining deep excavations

JUNO Conceptual Design Report

The Jiangmen Underground Neutrino Observatory (JUNO) is proposed to determine the neutrino mass hierarchy using an underground liquid scintillator detector. It is located 53 km away from both Yangjiang and Taishan Nuclear Power Plants in Guangdong, China. The experimental hall, spanning more than 50 meters, is under a granite mountain of over 700 m overburden. Within six years of running, the detection of reactor antineutrinos can resolve the neutrino mass hierarchy at a confidence level of 3-4$\sigma$, and determine neutrino oscillation parameters $\sin^2\theta_{12}$, $\Delta m^2_{21}$, and $|\Delta m^2_{ee}|$ to an accuracy of better than 1%. The JUNO detector can be also used to study terrestrial and extra-terrestrial neutrinos and new physics beyond the Standard Model. The central detector contains 20,000 tons liquid scintillator with an acrylic sphere of 35 m in diameter. $\sim$17,000 508-mm diameter PMTs with high quantum efficiency provide $\sim$75% optical coverage. The current choice of the liquid scintillator is: linear alkyl benzene (LAB) as the solvent, plus PPO as the scintillation fluor and a wavelength-shifter (Bis-MSB). The number of detected photoelectrons per MeV is larger than 1,100 and the energy resolution is expected to be 3% at 1 MeV. The calibration system is designed to deploy multiple sources to cover the entire energy range of reactor antineutrinos, and to achieve a full-volume position coverage inside the detector. The veto system is used for muon detection, muon induced background study and reduction. It consists of a Water Cherenkov detector and a Top Tracker system. The readout system, the detector control system and the offline system insure efficient and stable data acquisition and processing.Comment: 328 pages, 211 figure

Strata Movement Study Using a 250 m Deep Inclinometer Borehole, Huntly East Coalmine, New Zealand

Strata movement has adverse impacts on structures located on the surface and in the subsurface within a subsidence basin or affected area. Damages to a mine shaft may result from lateral movement and/ or vertical subsidence of the strata at a depth when the resultant stress is larger than the strength of the lining. My study was developed in collaboration with Solid Energy NZ Limited. My research concentrated on monitoring a 250 m deep borehole to assess changes of strata movement that occurred as underground mining approached the inclinometer borehole. The borehole was a simulation of a proposed shaft. The objectives of my research were to study strata movement characteristics above and adjacent to the North 5 coal mining area by monitoring the inclinometer and interpreting the reading data collected from the inclinometer borehole as the underground mining advanced; develop a model of subsidence using Phase2 software; then compare the modelling subsidence with what we have measured to identify any correlation or difference. The inclinometer borehole was located west of Te Ohaki Road, 300 m from the location of a proposed shaft in the adjacent panel in the Huntly East Mine. A total of 13 sets of inclinometer measurements were undertaken over two years from March 2009. Measurement stopped on 11 March 2011 because the probe could not be lowered through a depth of approximately 38 m in the borehole. My study uses ‘extraction vector’, and ‘movement trajectory of the borehole’ for analysing and interpreting the deep borehole movement in underground mining, and addresses the far field subsidence movement as to its potential impact on structures on the surface or in the subsurface. This thesis also introduces the concept of negative vertical additional friction, developed in China, which is a potentially helpful concept for this study, and the proposed shaft project. Three major movement zones were identified, two ‘shear zones’ from 135.0 to 135.5 m and from 166 to 170 m, and one ‘creeping zone’ from the surface to 115 m. The borehole movement was presented by the trajectory of the intersection of the borehole at depths of surface (1 m), 135 m, and 166 m. The two shear zones occurred on the bedding planes in Te Kuiti Group, the creeping zone occurred in the weak strata of the Tauranga Group and upper Te Kuiti Group. The borehole movements were non-linear, and the borehole lateral movement trajectories varied with depth. Three polynomial equations were developed from regression and modelling for indicating the relationship and predication between the nearest extraction distance and the induced lateral movement. The installation of an inclinometer borehole deeper than 120 m was not found in around 100 literature articles reviewed. No reports of use of inclinometer monitoring of ground movement induced by underground extraction were found in the literature reviewed. According to ASTM (2005), no standards are available yet for evaluation against precision and bias issues arising from use of borehole inclinometer. Therefore, the inclinometer borehole in this study may be one of the most complicated cases for monitoring and measurement of strata movement induced by the underground extraction in New Zealand

Proceedings Of The International Workshop On Numerical Modeling For Underground Mine Excavation Design

Numerical models play a significant role in the design of safe underground mining excavations and support systems. Advances in the capabilities of numerical modeling software, together with ever increasing computational speeds, have made it possible to investigate the very nature of the large-scale rock mass and its response to mining excavations. The improved understanding of the rock response obtained from modeling enhances our designs, resulting in greater stability and safety of the mining excavations. To help advance the state of the art in this field, the National Institute for Occupational Safety and Health organized the International Workshop on Numerical Modeling for Underground Mine Excavation Design. The workshop was held in Asheville, NC, on June 28, 2009, in association with the 43rd U.S. Rock Mechanics Symposium. The proceedings include 10 papers from leading rock mechanics and numerical modeling experts in the United States, Canada, Australia, and Germany. The papers address a wide range of issues, including various numerical modeling approaches, rock mass modeling, and applications in coal and metal mines