Geology for Underground Rocks (original) (raw)
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Rock mechanics or rock engineering was developed since the 1960s, but the underground excavation in rocks is still at its infant stages. The construction and maintenance of underground rock tunnel or caverns require prudent and detailed designs in the excavation process. To be able to predict the effects of the excavation process and estimate the effectiveness of the support designs, one has to understand the properties of the rock materials and their likely behaviour with the physical elements. This places great importance on the study of the deformation of the rock tunnel during excavation, particularly because deformations such as inward displacement can influence its stability. In this project, using stress analysis, investigations on the extent of deformation of rock tunnels during excavation will be conducted. Also uncover out the factors that contribute to the instability and displacement of underground excavations.
Geomechanical Modeling of In-Situ Stresses Around a Borehole
Borehole A coustics and Logging …
In this paper, we present a modelling of the in-situ stress state associated with the severe hole enlargement of a wellbore. Geomechanical information is relevant to assure wellbore stability, i.e., to prevent damages in the formation and later on, the casing. Many of the drilling parameters, as mud weight or the optimal orientation of the borehole, require some knowledge of the mechanical behaviour of the rock. The lack of these kind of data in exploratory areas, where there are usually insufficient constraints for the geological model, increases even more the risk, hence the costs. The present model uses the concepts of poroelasticity theory to compute the stationary 2D, brittle response of the formation around a borehole that is submitted to effective compressive horizontal stresses. The numerical solution is obtained using a finite element approximation. The initial stress state at the far field was estimated combining a frictional-failure theory with the observations of dipmeter caliper in a particular borehole that presents elongations in a preferential direction. The direction and relative extension of the observed breakouts at a particular depth are modelled successfully using formation realistic parameters and dimensions, although the exact shape of the borehole (at all angles) was unknown. For the particular case study, the orientation of the breakout is NE-SW, at about 82 degrees azimuth. Therefore, the maximum horizontal stress lies at approximately 350 degrees azimuth. The ratios of horizontal principal stresses to vertical stress that best honor the observations are SHmax = 2.3Sv and Shmin = 1.7Sv. The compressive strength necessary for the rock to fail, as indicated by the caliper data under this stress field, is about 140 MPa.
Rock mechanics issues in petroleum engineering
Historically, petroleum engineers have neglected the role of the physical porous medium except for its storage properties (porosity, thickness, areal extent) and its delivery capabilities (permeability, natural fractures, susceptibility to damage). Engineers charged with maximizing hydrocarbon recovery address rock mechanics issues only of dire necessity and then with little enthusiasm. Rock stresses and failure criteria are the most critical aspects of rock engineering for petroleum engineers. Horizontal drilling has presented a host of new issues that are more pervasive than are vertical well issues. This paper addresses several areas, including: • an overview of rock mechanics issues of importance to petroleum engineers, • a discussion of typical stress magnitude measurements routinely used, • a brief review of stress orientation and • a discussion of the rock mechanics issues critical to horizontal wells.
Mining of Mineral Deposits, 2024
This study aims to investigate fluid flow and heat transfer within rocks containing boreholes, focusing on the complex mechanisms within hot reservoirs. Non-commercial finite element (FE) software is used to visualize and present the results. Methods. The study involved the use of FE method with Visual Finite Element Analysis (VisualFEA) software to analyze the coupled phenomena of fluid flow and heat transfer in a rock sample. Special attention was given to incorporating material structure and geotechnical analysis in the software, as well as the treatment of cracked elements. In addition, the validation was done by comparing the current numerical solution using VisualFEA with the numerical solution using ANSYS Software. Findings. The study findings highlight the capabilities of VisualFEA software to accurately represent fluid flow, stress, and heat transfer in borehole-containing rocks. The results include insights into flow direction within the borehole, temperature distribution, and the validation of the software performance against expected system behavior. The study demonstrates the effectiveness of VisualFEA in handling complex loading and its ability to visualize multiple flow directions within a 2D model. The results are presented in the form of contours and curves. Originality. This study contributes to the field demonstrating the application of VisualFEA software in analyzing fluid flow and heat transfer in rocks with boreholes. The focus on incorporating material structure, geotechnical analysis, and treatment of cracked elements adds originality to the study, providing a comprehensive understanding of the coupled phenomena in hot reservoirs. Practical implications. The practical significance of this study is in the validation and benchmarking of VisualFEA software for studying fluid flow and heat transfer in geotechnical application. The findings can be utilized by geotechnical engineers and researchers to better understand the behavior of borehole-containing rocks under specific pressure and thermal loading conditions. The insights gained from this study can be used in decision-making processes related to resource mining, reservoir engineering, and geothermal energy use.
Analysis Of Geomechanical Properties In Well Design And Well Optimization .
International Journal of Engineering Sciences & Research Technology, 2012
Main aspect in wellbore instability is the selection of an appropriate rock failure criterion. This criterion i only the maximum and minimum principal stresses 2 σ has no influence on the rock strength. When Mohr experimental evidence from conventional triaxial test ( Coulomb criterion has been extensively used to represent rock failure under the polyaxial stress state ( 3 2 σ σ = ). In contrast to the prediction of redistribution Mohr suggest that 2 σ thus indeed have a strengthening effect. This research shown that Mohr only represent, that triaxial stress state ( linear failure criterion has been justified by experimental evidence from triaxial tests as well as polyaxial test. It is natural extension of the classical Mohr only represents rock failure under triaxial stress state, it is expected to be conservative in predicting well bore instability. The 3D analytical model employed by Mogi to calculate the stresses. A model was developed of the formation was found to be 0.9180psi/ft and decreases to 0.420psi/ft at depth 7300ft. The membrane efficiency of the formation increases from 0.698 to 0.719 at the depth considered Keywords: Wellbore instability, Rock failure criterion, Polyaxial test, pore pressure, membrane efficiency. out the entire life of a field. Borehole instability during drilling can take many familiar forms, such as stuck pipe, hole squeezing, lost circulation, severely enlarged hole or difficult direction control. Many related problems could arise when such wells are drilled to target, including uncertain formation evaluation, poor cementing, causing deformation and ineffective perforation. Problems of wellbore instability cost the industry several billions of dollars a year estimated to about 0.5 USD/ Year around the globe in downturn, well construction costs and lost production. Most of the instability problems encountered in the industry are mainly shale related, though it could also occur in unconsolidated sandstones as formation wash evaluation, shale's are low permeability media that does not experiences normal fluid loss and far dissipation when exposed to mud at over balance during drilling. As oil reservo need to drill extended reach holes with open holes internal also will increase. This requirement will be interfaced with the need to protect the environment against possible pollution in the past oil based mud (OBM) hav typically justified on the basis of borehole stability, fluid loss filter cake quality, lubricity and temperature stability.
Geomechanics applied to reservoir development in the coso geothermal field
2005
The Coso geothermal field is located approximately 220 kilometers north of Los Angeles, CA. In 2002, a project began to develop the east flank of the Coso geothermal field into an enhanced geothermal system (EGS); in such a system water is injected via injection well(s) into hot dry basement rock through naturally occurring or stimulated fractures. The injected water gathers heat from the reservoir rock before being extracted for direct use or energy production. To develop such a reservoir, adequate understanding of the reservoir geomechanics is necessary. This thesis investigates the state of stress and rock fractures, the existing permeable fractures in the reservoir, and the effects of water injection into fractures at the Coso EGS. A lower bound estimate of the magnitude of the maximum horizontal in-situ stress (S Hmax) was obtained using a fracture mechanics approach incorporating thermal effects on drilling induced fractures in well 38C-9. The maximum principal stress was found to transition from horizontal (σ 1 = S Hmax) to vertical (σ 1 = S v). A fracture propagation study was applied to compare the estimate presented herein with other published estimates that utilized frictional faulting and rock strength theory. The results showed the lower bound estimate resulted in little or no fracture propagation away from the wellbore; published estimates predicted extensive fracture propagation away from the wellbore. xvii The state of the jointed rock mass was characterized based on formation microscanner (FMS) data as they applied to the joint network fractures with significant aperture (Rose et al, 2004). The joint network supported the stress regime concluded from the state of stress estimation. A linear and non-linear failure criterion was applied to investigate critically and non-critically stressed joints, also the pore pressure increase required to critically stress non-critically stressed joints was found. At the proposed injection depth, critically oriented joints with friction angles [ 25º were critically stressed. A plane strain mathematical model was developed to investigate induced effects of water injection into a permeable deformable fracture. Three fracture geometries were considered: (i) injection/extraction from a line fracture, (ii) injection into an infinite radial fracture, and (iii) injection into a joint. Expressions for the induced pressure and temperature in the fracture and reservoir rock were developed and used to develop expressions for the induced thermoelastic, poroelastic, and combined thermo-and poroelastic fracture width changes, and the resulting induced fracture pressure. Analytic solutions were derived utilizing constant injection and leak-off assumptions. It was found the poroelastic effects tend to close the fracture as a result of leakoff, while the thermoelastic effects tend to open the fracture as a result of the cold water injection into hot rock. For conditions in the Coso EGS, the thermoelastic effects are dominant. At early times and high injection rates, the poroelastic effects cannot be ignored when considering the induced pressure even though the effects on the fracture width are relatively small. The fluid/solid coupling incorporated into model (iii) can alter the fracture width and pressure.
Methodology for predicting and handling challenging rock mass conditions in hard rock subsea tunnels
The most challenging rock mass conditions in hard rock subsea tunnels are represented by major faults/weakness zones. Poor stability weakness zones with large water inflow can be particularly problematic. At the pre-construction investigation stage, geological and engineering geological mapping, refraction seismic investigation and core drilling are the most important methods for identifying potentially adverse rock mass conditions. During excavation, continuous engineering geological mapping and probe drilling ahead of the face are carried out, and for the most recent Norwegian subsea tunnel projects, MWD (Measurement While Drilling) has also been used. During excavation, grouting ahead of the tunnel face is carried out whenever required according to the results from probe drilling. Sealing of water inflow by pre-grouting is particularly important before tunnelling into a section of poor rock mass quality. When excavating through weakness zones, a special methodology is normally ap...
Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2007
A novel approach is developed to represent coupled thermal-hydraulicmechanical (THM) behavior of porous systems that incorporates the non-isothermal free and forced convection of a single component fluid in a non-boiling thermoelastic medium. The three-way simultaneous coupling between the THM triplet is currently linear, but no restriction is placed on incorporating material nonlinearities. The coupled PDEs are solved in space by grid-adaptive finite elements. The model is validated against solutions for linear non-isothermal consolidation of a column. We demonstrate the utility of the model by analyzing the behavior of a deep wellbore in a themoelastic medium circulated by a pressurized, but chilled fluid. Model results illustrate the significant importance of the cross-couplings between individual THM processes for the evaluation of wellbore stability.