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Pohang, South Korea

This study investigates characteristics of transient flow and the possibility of freezing in a pressure regulator and the rear connecting pipe of the pressure regulator during the closing process of the pressure control valve (PCV), which is an essential element in the operation of a natural gas pipeline network. For this purpose, the study develops a numerical model for the PCV and its rear connecting pipe by applying computational fluid dynamics method. The analysis is conducted in each of two cases: (1) a steady-state analysis in the case of normal operation and (2) an unsteady-state analysis in the case of emergency closure in problematic situations. First, we closely examine characteristics of internal flow in the pressure regulator and the rear connecting pipe when the PCV operates regularly with a 50% opening ratio in a steady state. Afterwards, unsteady-state analysis examines characteristics of transient flow, such as lowered pressure and temperature, velocity change, etc., of rear flow in the pressure regulator when the PCV is closed because of trouble in the pressure control system. © 2013 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.

McCullagh C.L.,Colorado School of Mines | Tutuncu A.N.,Colorado School of Mines | Song T.H.,KOGAS
48th US Rock Mechanics / Geomechanics Symposium 2014 | Year: 2014

In this paper, the use of microseismic data for calibration and modification of wellbore temperature models will be introduced. Moreover, fracturing fluid distribution obtained using the modified temperature numerical model is coupled with the microseismic field data for several Eagle Ford shale wells to improve hydraulic fracture stimulation characterization. By measuring the temperature change along the wellbore, distributed temperature sensing (DTS) data may provide relative fluid distribution. This information may be used to assess the simple geometry of the hydraulic fractures, the fracture initiation points along the wellbore, wellbore integrity issues, and the effectiveness of isolation tools. With recently published wellbore temperature models, quantitative information about which zones receive the stimulation fluid can be numerically solved. However, DTS measurements and fluid distributions calculated using DTS data are restricted to the wellbore and near wellbore environment. For far field diagnostics of hydraulic fracturing stimulation other measurements are needed, specifically microseismic. By combining these two measurements, a new workflow is created which incorporates both the far field and wellbore measurements to characterize hydraulic fractures, both real-time and after the stimulation job. This workflow is especially useful in reservoirs that are naturally fractured or in wellbores were stress shadowing effects are significant, such as multistage fracturing multiple wells that are in close proximity to each other. In these scenarios the path that the fluid travels may be complex, even in the near wellbore environment. Due to this complexity, fluid distributed calculations based on DTS data may provide misleading results. Using information gained from microseismic, the wellbore temperature models may be modified to increase the reliability of the numerically calculated fluid distributions. The purpose of this paper is to propose how microseismic data may be used to modify the wellbore temperature models, and how stimulation fluid placement determined from the modified models may then be coupled with the microseismic to improve hvdraulic fracture stimulation characterization. Copyright (2014) ARMA, American Rock Mechanics Association

Kim K.-H.,Hanyang University | Sung W.-M.,Hanyang University | Han J.-M.,KOGAS | Lee T.-H.,Hanyang University
Geosystem Engineering | Year: 2012

To estimate methane recovery from an enhanced coal bed at the field scale, it is important to understand CO2 movement. Since coal beds are generally connected with aquifers, CO2 movement is affected by aquifer position and strength. Under conditions of no aquifer, CO2 initially has a tendency to move to the top layer of the coal seam due to the buoyancy effect. However, the permeability of the upper layer is decreased due to the swelling effect. The viscosity flow effectively improves CO2 movement due to high permeability in the bottom layer. Because of the offsetting effects of viscosity and gravitational flow, the vertical sweep efficiency of injected CO2 is very effective. Thus, methane recovery is highly calculated. Under conditions of an upper aquifer, CO2 flow in the bottom layer decreased as the injected CO2 leaked to the aquifer. As the hydraulic connection between the overlying aquifer and the coal seam is strong, the vertical sweep efficiency is weakened due to the high gas leakage rate. Therefore, methane recovery decreases. However, under conditions in which an aquifer is at the bottom, methane recovery should be high because the gas-leakage rate is almost negligible. Under conditions with an aquifer edge, injected CO2 in the coal bed has an asymmetric flow because pressure is only supported in the flow direction of the aquifer. As the pressure is greater at the aquifer, the asymmetric flow is gradually strengthened by changes in the equilibrium caused by viscosity and gravity. Consequently, enhanced coalbed methane recovery has irregular efficiency, in part due to the CO2 movement. However, by suitably adjusting the CO2 injection site and production well perforation, total methane recovery can be made more efficient, despite producing an asymmetric flow of injected CO2. These findings clearly indicate that production or injection plans for enhanced coalbed methane must be designed to consider CO2 movement. © 2012 Taylor & Francis.

Jang S.-H.,KOGAS
International Gas Research Conference Proceedings | Year: 2014

A presentation covers the balancing role of LNG in global gas market; effect of unconventional gas technology; US LNG exports; and globalization of LNG market. This is an abstract of a paper presented at the International Gas Union Research Conference (IGRC 2014) (Copenhagen, Denmark 9/17-19/2014).

Lee T.H.,Hanyang University | Lee Y.S.,KOGAS | Jang Y.H.,Hanyang University | Lee K.S.,Hanyang University | And 2 more authors.
Energy Sources, Part A: Recovery, Utilization and Environmental Effects | Year: 2012

According to the Nelson's classification scheme, naturally fractured basement reservoirs are Type 1 systems in which the fractures provide porosity and permeability. Hydrocarbon production from basement reservoirs only occurs through the connected fracture network. Thus, characterization and prediction of flow behavior in basement reservoirs is extremely difficult due to the heterogeneity of the fractures. In this study, a generalized multiphase discrete fracture network simulator was developed. The model implements 2D flow within a rectangular fracture, which is important in thick fractured reservoirs like basement rocks. The discrete fracture network model developed in this study was validated for two synthetic fracture systems using a commercial model, ECLIPSE. Comparison showed excellent agreement between the results for both models. To examine the changing production behavior in fractured basement reservoirs, an attempt was made to analyze the effect of a bottom-water aquifer on production behavior. It was confirmed that the discrete fracture network model is a useful tool in predicting water breakthrough and remaining oil phenomena. © 2012 Copyright Taylor and Francis Group, LLC.

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