Dae-Sung Cheon

Theoretical Background and Design of Hydraulic Fracturing in Oil and Gas Production

This paper deals with a hydraulic fracturing technique, which is one of the methods to maximize the recovery rate and productivity of oil and gas in the petroleum industry. In the hydraulic fracturing, typically water mixed with sand and chemicals is injected into a wellbore in order to create artificial fractures along which formation fluids migrate to the well. In recent years, it is widely used in non-conventional oil and gas such as oil shale and shale gas. Three main stages of the hydraulic fracturing process, the proposed design models for the effective hydraulic fracturing and diagnostics after fracturing treatment are introduced. In addition, this paper introduces reservoir geomechanics to solve various problems in the process of hydraulic fracturing.

Management and concept of the monitoring system considering the characteristics of subsea tunnels

In order to ensure the safety of the subsea tunnel during its construction and operation, unlike the underground structures on land, the special monitoring system is essential which considers the characteristics of subsea tunnels in addition to conventional stress and displacement measurements applied to existing land tunnels. Therefore, the concept applied to NATM is reorganized to evaluate the stability of subsea tunnels. And the observation system for making a monitoring plan, the critical strain theory for tunnel safety management and MS monitoring methods for detecting the local failure and crack initiation of rock and supports, are introduced. Finally, the scheme of monitoring and management for subsea tunnels by using these methods is suggested.

Case Study on Stability Assessment of Pre-existing Fault at CO 2 Geologic Storage

Abstract Increase of pore fluid pressure resulting from injection of CO 2 may reactivate pre-existing faults, and the induced seismic activities can raise the safety issues such as seal integrity, restoration of storage capacity, and, in the worst case, removal of previously injected CO 2 . Thus, fault stability and potential for CO 2 leakage need to be assessed at the stage of site selection and planning of injection pressure, based on the results of large-scale site investigations and numerical modeling for various scenarios. In this report, studies on the assessment of fault stability during injection of CO 2 were reviewed. The seismic activities associated with an artificial injection of fluids or a release of naturally trapped high-pressure fluids were first examined, and then site investigation methods for the magnitude and orientation of in situ stresses, the distribution and change of pore fluid pressure, and the location of faults were generally summarized. Recent research cases on possibility estimation of fault reactivation, prediction of seismic magnitude, and modeling of CO

Permeability change and geometrical information of void spaces in Berea sandstone and Otway sandstone

Abstract To clarify the differences in permeability and three-dimensional void geometry in two sandstones, permeability change by increasing confining pressure were measured and three-dimensional geometrical information with microfocus X-ray CT were analyzed. In this research, Berea sandstone and Otway sandstone were used as a specimen, and its total porosity measured by mercury intrusion porosimetry were 17.4 and 25.0%, respectively. Pore size distribution in both sandstones was almost same as one modal manner, but Otway sandstone specimen showed slightly narrow peak of 5 μ–7 μm. Permeability change in both sandstones was decreased with increasing effective confining pressure, but the absolute value in Otway sandstone was lower by one order of magnitude than those in Berea sandstone. Three-dimensional medial axis (3MDA) method was adopted to compare pore geometry in two sandstones and tortuosity, number of connecting paths were decided. Based on this information, we evaluated the relationship between permeability and pore structures.

Mechanical Properties of a Lining System under Cyclic Loading Conditions in Underground Lined Rock Cavern for Compressed Air Energy Storage

In a material, micro-cracks can be progressively occurred, propagated and finally lead to failure when it is subjected to cyclic or periodic loading less than its ultimate strength. This phenomenon, fatigue, is usually considered in a metal, alloy and structures under repeated loading conditions. In underground structures, a static creep behavior rather than a dynamic fatigue behavior is mostly considered. However, when compressed air is stored in a rock cavern, an inner pressure is periodically changed due to repeated in- and-out process of compressed air. Therefore mechanical properties of surrounding rock mass and an inner lining system under cyclic loading/unloading conditions should be investigated. In this study, considering an underground lined rock cavern for compressed air energy storage (CAES), the mechanical properties of a lining system, that is, concrete lining and plug under periodic loading/unloading conditions were characterized through cyclic bending tests and shear tests. From these tests, the stability of the plug was evaluated and the S-N line of the concrete lining was obtained.

A review of the effects of rock properties on waterjet rock cutting performance

ABSTRACT: The rock fracturing during waterjet cutting is very complicated because rock is inhomogeneous and anisotropic, compared with artificial materials (e.g., metal or glass). Thus, it is very important to verify the effects of roc k properties on waterjet rock cutting performance. Properties affecting the rock cutting efficiency have been variously described in the literature, depending on the experimental conditions (e.g., water pressure, abrasive feed rate, or standoff distance) and rock-types studied. In this study, a rock-property-related literature review was performed to determine the key properties important for waterjet rock cutting. Porosity, uniaxial compressive strength, and hardness of the rock were determined to be the key properties affecting waterjet rock cutting. The results of this analysis can provide the basic knowledge to determine the cutting efficiency of waterjet rock cutting technology fo r rock excavation-related construction.Keywords: High pressure waterjet, Abrasive waterjet, Rock property, Rock cutting

Estimation of the Characteristics of Delayed Failure and Long-term Strength of Granite by Brazilian Disc Test

Long-term stability and delayed failure of granite were evaluated through the laboratory test based on Wilkins method and Brazilian disc test (BDT) which yields tensile strength, mode I fracture toughness and subcritical crack growth parameters. Then, the long-term strength of granite was estimated by using analytical models and long-term stability of compressed air-energy storage (CAES) pilot cavern pressurized up to 5 ~ 6 MPa was evaluated using numerical code, FRACOD with the determined subcritical crack growth parameters. The results of test and analyses showed that the subcritical crack growth index, n was determined as 29.39 and the inner pressure of 5 ~ 6 MPa had an insignificant effect on the long-term stability of pilot cavern. It was also found that the measurement and analysis of acoustic emission events can describe the accumulation of damage due to subcritical crack growth quantitatively. That is, AE monitoring can provide the current status of rock under loading if we make an identical installation condition in the field with that of the laboratory test.

손상대를 고려한 암반사면 안정성 평가 및 인자분석

After excavation or blasting, rock properties within an excavation damaged zone can be perpetually weakened on account of stress redistribution or blasting impact. In the present study, the excavation damaged zone is applied to a rock slope. The objective of this research is to compare the mechanical stability of the rock slope depending on the presence of the damaged zone using 2-dimensional modeling and analyze factors affecting factor-of-safety. From the modeling, it was founded that the mechanical stability of the rock slope is significantly dependent on the presence of the damaged zone. In particular, factor-of-safety with a consideration of the damaged zone decreased by approximately 49.4% in comparison with no damaged zone. Factor analysis by fractional factorial design was carried out on factor-of-safety. It showed that the key parameters affecting factor-of-safety are angle of the slope, cohesion, internal friction angle and height.

Analysis of Whole Tunnel Stability by Using Rock Mass Classification and Mohr-Coulomb Analytical Solution

Finite element or difference methods are applied to the analysis of the tunnel stability and they provide detailed behaviour of analyzed tunnel sections but it is rather inefficient to analyze all the section of tunnel by using these methods. In this study, the authors suggest a new stability analysis method for whole tunnel to provide an efficient and easy way to understand the behaviour of whole tunnel by using an analytical solution with the assumption of equivalent circular tunnel. The mechanical behaviour, radial strain and plastic zone radius of whole tunnel were analyzed and appropriate support pressure to maintain the displacement within the allowable limit was suggested after the application of this method to the tunnel. Consequently, it was confirmed that this method can provide quick analysis of the whole tunnel stability and the quantitative information for subsequent measures such as selection of tunnel sections for detailed numerical analysis, set up of the monitoring plan, and so on.