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ABSTRACT: Mechanical and hydraulic properties of fractures are strongly affected by the exploitation of enhanced geothermal system (EGS) and unconventional reservoirs. This study attempts to reveal the evolution of shearing properties and fluid pressure heterogeneity of natural fractures, possibly caused by mud loss during drilling and hydraulic stimulation. A series of triaxial shear-flow and injection-driven shear numerical simulations were carried out using a coupled hydro-mechanical pore network method (PNM) in DEM. Fracture surface profiles were generated according to the X-ray computed tomography scanning data of open and closed joints of rock cores retrieved from a 4.2-km-deep well at the Pohang EGS site. We developed an algorithm to update the orientations of joint contacts automatically and overcome the mismatch between joint roughness and contact direction especially at large shear displacement. A refreshing fluid grids approach based on the PNM is modified by Delaunay triangulation and Kriging interpolation. The results indicate that injection has caused pressure heterogeneity in the pressurized area. Localized shear rupture could occur in the area with highly concentrated pore pressure. These characteristics also emphasize the significant cause of fluid pressure heterogeneity in rupture propagation in a fracture, likely resulting in unstable slip of critically stressed preexisting faults after small fluid pressure perturbations. 1. INTRODUCTION Mechanical and hydraulic properties of fractures are strongly affected by the exploitation of enhanced geothermal system when hydraulic stimulation is utilized to enhance the permeability of hot dry rock (Rathnaweera et al., 2020). Anthropogenic fluid injections into rock crust can generate seismicity (Guglielmi et al., 2015; An et al., 2020), which brings more challenges to exploit this clean energy. For instance, an Mw 5.5 earthquake, one of the most damaging events in South Korea, was induced by hydraulic stimulation in 4.2-km-deep granodiorite. After 2 years’ hydraulic stimulation, highly localized fluid pressurization and perturbation induced by hydraulic stimulation destabilized and activated the fault where the main shock happened (Kim et al., 2018; Gorigli et al., 2018). Many injection-driven shear tests experiments and numerical computation have been carried out to investigate injection-induced fracture instability. Ji et al. (2020, 2021) carried out triaxial shear-flow experimental tests and COMSOL numerical simulations to recover fluid pressure heterogeneity on rock fractures. Fluid pressure heterogeneity on a rock fracture may induce localized shear rupture and propagates to activate the entire fracture. Analytical models that could describe the decrease of frictional strength of a rock fracture and predict potential seismic events have been proposed (Wei et al., 2021; Ji et al., 2021).
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (0.70)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Renewable > Geothermal > Geothermal Resource (0.74)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
- Reservoir Description and Dynamics > Non-Traditional Resources > Geothermal resources (1.00)
Effect of Pressurization Rate and Fluid Viscosity on Hydraulic Fracturing Process of Pocheon Granite
Kim, K. Y. (Korea Maritime and Ocean University / Korea Institute of Civil Engineering and Building Technology) | Diaz, M. (Korea Maritime and Ocean University / Korea Institute of Civil Engineering and Building Technology) | Jung, S. G. (University of Science and Technology) | Guinot, F. (From Bottom to Top) | Min, K.-B. (Seoul National University) | Zang, A. (German Research Center for Geosciences) | Stephansson, O. (German Research Center for Geosciences) | Zimmermann, G. (German Research Center for Geosciences) | Hofmann, H. (German Research Center for Geosciences) | Yoon, J. S. (DynaFrax UG)
ABSTRACT In this study, a series of hydraulic fracturing tests under different injecting conditions was performed on Pocheon granite rock to account for the evolution of hydro-mechanical behavior during the fracturing process. We investigated the effect of the fluid viscosity and pressurization rate on the fracturing process of granite. Two different type of injection fluids, water and oil, were used under different pressurization rate. Visual inspection techniques such as X-ray computed tomography and thin section imaging were employed to capture the fracture pattern together with AE monitoring. As a result, the water injection case has larger saturation zone into the formation at breakdown while the oil infiltrates only vicinity of main fracture. The AE monitoring results show that the oil injection cases have a big sudden rise in the cumulative AE hit energy during fracture propagation which is more manifest under high pressurization rate. The induced fractures are observed to be larger in aperture and less tortuous for the higher fluid viscosity and higher pressurization rate cases through thin section images. On the other hand, the sleeve testing cases yield relatively very small aperture of induced fractures. 1. INTRODUCTION Hydraulic fracturing (HF) is a stimulation technique that has been widely used to increase the permeability for the development of conventional and unconventional oil and gas as well as geothermal reservoir. During HF, a pressurized fluid is injected into the formation to initiate and extend fractures into the reservoir (Mack and Warpinski, 2000). Recent remarkable development in Enhanced geothermal system (EGS) also relies on HF though there have been various reports on unwanted levels of induced seismicity. In EGS, the target rock type is mostly crystalline rock e.g., granite and granodiorite which has been less studied in relation to hydraulic stimulation compared to sedimentary rocks which are the main interest to oil and gas industry. In addition, hydraulic stimulation in crystalline rock is thought to yield favorably hydro-shearing due to the slip of pre-existing discontinuities that result on self-propped induced fractures (Xie et al, 2015).
- Geology > Rock Type > Igneous Rock > Granite (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Non-Traditional Resources > Geothermal resources (1.00)
Enhancement Mechanisms of Induced Seismicity by Site-Specific Operational and Geological Features in a Poroelasticity System
Chang, K. W. (Sandia National Laboratories) | Yoon, H. (Sandia National Laboratories) | Kim, Y.-H. (School of Earth and Environmental Sciences, Seoul National University) | Lee, M. Y. (Sandia National Laboratories)
ABSTRACT Recent occurrence of moderate to large seismic events (Mw ≥ 3) after terminating well operations is unlikely to be caused only by pore-pressure diffusion into conductive faults; it is necessary to address additional mechanisms in the earthquake nucleation. Our coupled fluid flow and geomechanical model describes the processes inducing seismicity corresponding to the sequential stimulation operations in Pohang, South Korea. Simulation results show that the combined effect of poroelastic shearing and delayed pore-pressure accumulation can cause slip on a fault, potentially inducing the post shut-in large earthquakes. Alternate injection-extraction operations through multiple wells can enhance the efficacy of pore-pressure diffusion and subsequent stress transfer through rigid and low-permeability basement rocks to the fault. This mechanistic study addresses that comprehensive characterization of the faulting system and optimal injection-extraction strategies are critical to mitigate unexpected seismic hazards associated with the site-specific uncertainty in operational and geological factors. 1. INTRODUCTION Over the past decade a number of induced seismic events have been increasingly observed due to extensive subsurface energy activities such as wastewater injection [e.g., Kim, 2013, Hornbach et al., 2016], geothermal stimulation [e.g., Diehl et al., 2017], or geological carbon storage [e.g., Bauer et al., 2016]. Numerical models provide a critical link between field observations and theory of mechanisms inducing earthquakes by quantifying transient perturbations in pore pressure and stresses throughout a domain of interest. At the Pohang site in South Korea (Fig. 1), the first EGS (Enhanced Geothermal System) stimulation began on 29 January 2016 and total of five phases of injectionproduction operations had taken place at ∼4.3 km of depth through PX-1 and PX-2 wells until September 2017 with a net injected volume of 6,000 m3 (total injected volume of 12,800 m3 and total produced volume of 6,800 m3). The spatial footprint of detected seismic events delineates the geometry of the fault plane (strike/dip = N214°/43°NW), separating PX-1 and PX-2 [GSK, 2019], which was not found prior to the EGS stimulation. The focal mechanisms indicate that the Korean Peninsula is under tectonic compression, and the local stress field reveals that the 2017 Pohang earthquake was induced by the oblique reverse slip of a previously extensional fault at optimal orientation. This fault was critically stressed, implying that a fault slips with a small stress perturbation, and drilling or fluid injection-production initiated seismic activities along the fault.
- North America > United States (1.00)
- Asia > South Korea > Gyeongsangbuk-do > Pohang (0.68)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Energy > Renewable > Geothermal (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.70)
- North America > Canada > Saskatchewan > Western Canada Sedimentary Basin > Alberta Basin (0.99)
- North America > Canada > Northwest Territories > Western Canada Sedimentary Basin > Alberta Basin (0.99)
- North America > Canada > Manitoba > Western Canada Sedimentary Basin > Alberta Basin (0.99)
- (3 more...)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Non-Traditional Resources > Geothermal resources (1.00)
ABSTRACT In 2018, fracture caging was introduced as a concept to control hydraulically stimulated fracture extents and to contain fluid flow within targeted rock volumes in the subsurface. When implemented via stochastic design of well fields, caging has significant potential for bringing a successful outcome for the control of subsurface fracture fluid flow without requiring very much information about the subsurface. Contained high-pressure fluid injection brings the benefit of preventing pore pressure increase away from the intended injection zone. Therefore, caging offers a means to prevent large earthquakes that could otherwise be caused by injection activities. Here we present evidence of this phenomenon by evaluating available field data from a contained enhanced geothermal system in relation to non-caged injection-dominated sites. We also discuss a possible mechanism by which caging could directly control the maximum magnitude of injection induced seismicity. Long term, if caging is ultimately found to be effective for controlling seismicity, we would be able to prevent another Pohang-type damaging induced earthquake event. 1. INTRODUCTION At the ARMA symposium and the Stanford Geothermal Workshop in 2018, the concept of ‘fracture caging’ was introduced (Frash et al., 2018a,b). This concept involved pre-drilling tactical patterns of production wells around injection wells to contain hydraulic fracture extents inside a targeted volume of rock (Fig 1). Laboratory experiments and numerical modelling confirmed that fracture extents could be contained. Next at ARMA in 2019, we proposed a stochastic method to design suitable well layouts that take advantage of this effect to control fractures and fluid flow in the subsurface (Frash et al., 2019). This analysis supported the notion that fracture caged systems could be created in rock systems containing fractures at unknown locations and unknown orientations. Recently, analysis of microseismic data from field and laboratory experiments has revealed that fracture caging could offer a means to limit the number and the magnitude of seismic events (Frash et al., 2020). Here, this evidence is presented and a mechanism is proposed in an attempt to explain how fracture caging could limit the maximum magnitude and number of induced seismic events. If correct, a mechanism such as this could offer a means to directly control induced seismicity and a means to prevent damaging induced seismic events.
- North America > United States (1.00)
- Asia > South Korea > Gyeongsangbuk-do > Pohang (0.61)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Renewable > Geothermal > Geothermal Resource (0.49)
- Government > Regional Government > North America Government > United States Government (0.46)
- Europe > France > Nouvelle-Aquitaine > Lacq Basin > Lacq Field (0.99)
- North America > Canada > Alberta > Colorado Field > Bonavista Colorado 6-32-90-4 Well (0.97)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Non-Traditional Resources > Geothermal resources (1.00)
Cyclic Hydraulic Stimulation Design to Develop Enhanced Geothermal Systems
Zimmermann, G. (Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences) | Hofmann, H. (Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences) | Zang, A. (Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences) | Stephansson, O. (Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences) | Farkas, M. (Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences) | Yoon, J. S. (Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences) | Zhuang, L. (Korea Institute of Civil Engineering and Building Technology) | Kim, K. Y. (Korea Institute of Civil Engineering and Building Technology) | Min, K.-B. (Seoul National University)
Abstract Enhanced Geothermal Systems (EGS) are required to extract economic amounts of heat from low permeable geothermal reservoirs. In this context we applied hydraulic stimulation scenarios of various cyclic stimulation designs. The general aim is to reduce the risks of unwanted seismic events beyond a certain threshold depending on the vulnerability and exposure of people, buildings and infrastructure. The case studies include hydraulic stimulation designs from experiments at different scales of investigation. Experiments on the laboratory scale revealed a reduction of formation breakdown pressure for cyclic loading and were visualised by CT scans. A new advanced protocol of progressively increased cyclic injection and a pulsed injection design for hydraulic fracturing experiments was applied at the Hard Rock Laboratory in Äspö in Sweden. The dynamic stimulation scheme of loading and unloading at the fracturing net pressure of each cycle led to a lower accompanied seismicity but simultaneously increased the permeability of the treated rock intervals. Based on these experiences a specially adjusted protocol for a field experiment was set up for the EGS site in Pohang, Republic of Korea. The general aim was to keep the seismicity below a tolerable magnitude and develop a suitable downhole heat exchanger. 1 Introduction The general aim of stimulation is to develop an advanced injection strategy to control the fracture propagation and simultaneously reduce the risks of unwanted seismic events beyond a certain threshold depending on the vulnerability and exposure of people, buildings and infrastructure (Majer et al. 2007). In this context many efforts have been made to develop stimulation concepts to mitigate the risk of unwanted high seismicity and simultaneously enhance the permeability of the rock. One option to optimize the development of fracture networks based on hydraulic fracturing treatments is a cyclic injection scheme. An early study applying a cyclic stimulation scheme was carried out by Kiel (1977) to develop long and branching fractures in natural fractured formations in US petroleum basins. He named this treatment dendritic fracturing, and it resulted in a much higher productivity enhancement compared to conventional hydraulic treatments. The scheme includes an alternation of injection stages and shut-in or flow back (also called bleed off), and the basic idea behind this is a relaxing process by reducing the fracture net pressure after each injection stage. He argued that this causes the production of spalls from the asperities of the fracture faces, which can then act as proppants and increase the fracture conductivity. Subsequent stages of cyclic injection result in spalling and branching of secondary fractures.
- Asia > South Korea > Gyeongsangbuk-do > Pohang (0.28)
- Europe > Sweden (0.27)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Renewable > Geothermal > Geothermal Resource for Power Generation > Enhanced Geothermal System (0.62)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Non-Traditional Resources > Geothermal resources (1.00)
Numerical Investigation of Cyclic Hydraulic Stimulation and Related Induced Seismicity in Pohang Fractured Geothermal Reservoir
Farkas, Marton Pal (University of Potsdam) | Hofmann, Hannes (German Research Centre for Geosciences) | Zimmermann, Gunter (German Research Centre for Geosciences) | Zang, Arno (German Research Centre for Geosciences) | Yoon, Jeoung Seok (German Research Centre for Geosciences)
ABSTRACT: In this study we investigate numerically the flow rate controlled cyclic stimulation experiment performed in August 2017 at the Pohang EGS site using the finite element code FracMan. Per definition, a soft stimulation method aims to increase permeability while reducing the risk of inducing larger seismic events. The numerical code enables studying hydro-mechanical processes and investigating main characteristics of induced seismicity such as spatial evolution of events and their moment magnitude in relation to injected fluid volume in three dimensions. The analysis contributes to understanding the fracturing processes and induced seismicity in naturally compartmentalized fractured reservoir. The code can be also used for predicting the relationship between fluid injection volume and spatial extent of generated or reactivated fractures, i.e. the stimulated reservoir volume. The reservoir model will eventually allow different injection strategies to be investigated to design an optimal stimulation procedure ahead of future field application of soft stimulation. Furthermore, it may also serve as a basis for future numerical investigations.
- North America > United States (1.00)
- Europe (0.70)
- Asia > South Korea > Gyeongsangbuk-do > Pohang (0.63)
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology (0.95)
- Energy > Renewable > Geothermal (1.00)
- Energy > Oil & Gas > Upstream (1.00)
Comparison of Cyclic and Constant Fluid Injection in Granitic Rock at Different Scales
Hofmann, H. (Helmholtz Centre Potsdam GFZ German Research Centre) | Zimmermann, G. (Helmholtz Centre Potsdam GFZ German Research Centre) | Zang, A. (Helmholtz Centre Potsdam GFZ German Research Centre) | Yoon, J. S. (Helmholtz Centre Potsdam GFZ German Research Centre) | Stephansson, O. (Helmholtz Centre Potsdam GFZ German Research Centre) | Kim, K. Y. (Korea Institute of Civil Engineering) | Zhuang, L. (Korea Institute of Civil Engineering) | Diaz, M. (Korea University of Science and Technology) | Min, K.-B. (Seoul National University)
ABSTRACT: Exploitation of unconventional energy resources often requires fluid injection to improve the hydraulic performance of the reservoir. A potential risk associated with these hydraulic stimulation treatments is the unintended development of manmade seismic events. Therefore, mitigation measures for seismic risks associated with fluid injection is of major importance for many applications, such as shale gas, tight oil and enhanced geothermal systems (EGS). As part of a portfolio of options, cyclic injection schemes were recently proposed to reduce the risk of inducing larger seismic events. To prove this concept, a series of experiments with cyclic and constant fluid injection rates were performed in granitic rocks at laboratory scale (Pocheon Granite), at mine scale (Àspo Hard Rock Laboratory, Sweden) and at field scale (Pohang EGS site, Korea). All experiments have in common that the hydraulic performance could be improved with lower magnitude seismic events and lower breakdown pressure, thus showing the potential to mitigate seismic risk of hydraulic stimulation treatments.
- Europe (1.00)
- North America > United States (0.93)
- Asia > South Korea > Gyeongsangbuk-do > Pohang (0.25)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.34)
- Energy > Renewable > Geothermal (1.00)
- Energy > Oil & Gas > Upstream (1.00)
First Hydraulic Stimulation in Fractured Geothermal Reservoir in Pohang PX-2 Well
Park, Sehyeok (Seoul National University) | Xie, Linmao (Seoul National University) | Kim, Kwang-Il (Seoul National University) | Kwon, Saeha (Seoul National University) | Min, Ki-Bok (Seoul National University) | Choi, Jaiwon (NexGeo Inc.) | Yoon, Woon-Sang (NexGeo Inc.) | Song, Yoonho (Korea Institute of Geoscience and Mineral Resources)
Abstract The first hydraulic stimulation for enhanced geothermal system (EGS) development in Korea had been conducted in the PX-2 well of 4,348 m depth in Pohang EGS site from January 29 to February 20, 2016. Treatment histories of injection rate, wellhead pressure and corresponding induced microseismicity data were obtained from the stimulation test upon 140 m long open hole section at the well bottom. Wellhead pressure was up to 89 MPa and considerable level of flow rate was attempted up to 47 L/sec. Microseismicity observation showed a trend of lager and more frequent seismicity occurrence in shut-in phase than in injection phase. The injectivity index during the stimulation periods had increased as 2.7 times in January 30 at the wellhead pressure of 73 MPa. Postulating the existence of a major fracture zone intersecting the open hole section, the transmissivity and the corresponding equivalent aperture of the fracture were evaluated. Required breakdown pressures by hydrofracturing and hydroshearing mechanisms were estimated based on the various scenarios on the in-situ stress condition, major fracture zone orientation and shear failure criteria. 1. Introduction 1.1. Pohang EGS development site The first enhanced geothermal system (EGS) development project in Korea was launched at the end of 2010 in Pohang. Five boreholes are located within 5 km from the site (Fig. 1): BH-1 of 1.1 km depth, BH-2 of 1.5 km depth, BH-3 of 0.9 km depth, BH-4 of 2.4 km depth, and EXP-1 of 1 km depth. The Pohang EGS site is owned and operated by NexGeo Inc., and it is located at 129°22'46.08″E, 36°06'23.34″N. Drilling of PX-1 and PX-2 wells were finished with final depths of 4,127 m and 4,348 m, respectively, and it is planned to be expanded to a triplet system, i.e., a fluid circulation system with three wells in the target reservoir, after stimulations in PX-2 and PX-1.
- Energy > Renewable > Geothermal (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Oceania > Australia > South Australia > Cooper Basin (0.99)
- Oceania > Australia > Queensland > Cooper Basin (0.99)
On-Line Prediction Model for Rate of Penetration (ROP) With Cumulating Field Data in Real Time
Diaz, Melvin B. (University of Science and Technology, Korea) | Kim, Kwang Yeom (Korea Institute of Civil Engineering and Construction Technology) | Shin, Hyu Soung (Korea Institute of Civil Engineering and Construction Technology)
Abstract We present an optimized training and prediction model for Rate of Penetration (ROP) forecasting using on-line artificial neural network (ANN) in real-time. The technique aims to assist decision making on drilling operations by predicting ROP under a given set of drilling conditions. The scenario modeler relies on real time drilling data analysis, and it is capable of handling cumulative information analysis in real time for ROP prediction within the same well, but also can consider drilling data gained from other fields under similar conditions. The real time prediction model has been applied to drilling data coming from a geothermal project of over 4 km depth, located in the Pohang, Republic of Korea. The observed results with respect to data intervals or sections set the basis for further adjustments to the model, and encourages its use in different drilling situations. 1. Introduction ANN have been applied to a wide variety of field research areas that include computer vision, speech recognition, and petroleum engineering (Bilgesu et al., 1997). Especially, in the aforementioned field, ANN have been used for ROP forecast (Gidh et al., 2012). It has been shown that this technique is dependent on the size and accuracy of the input parameters, and in general the more number of data points, the better the results. Its ability to consider more drilling parameters into the model makes it advantageous (Monazami et al., 2012). During ANN learning phase, a selected group of input parameters are provided to the model and they serve to train the algorithm. Two basic types of learning modes can be mention, On-line and off-line training, and they distinguish from each other basically on the training cases are managed after training (Shin 2001). In on-line training, the provided input parameters are discarded after being processed, however the weights are updated. Owing to the accumulative manner the drilling data is generated in the field, this work explores the applicability of an artificial neural network with an on-line training mode for ROP prediction especially in subsequent drilling sections within the same well.
- Asia > South Korea > Gyeongsangbuk-do > Pohang (0.25)
- Europe > United Kingdom > North Sea > Southern North Sea (0.25)
- Well Drilling > Drilling Operations (1.00)
- Data Science & Engineering Analytics > Information Management and Systems > Neural networks (0.97)
- Data Science & Engineering Analytics > Information Management and Systems > Artificial intelligence (0.69)
- Reservoir Description and Dynamics > Non-Traditional Resources > Geothermal resources (0.68)
Numerical Modeling of Coupled Hydromechanical Behavior of Fractured Geothermal Reservoir at Pohang Enhanced Geothermal System (EGS) Site
Yoo, Hwajung (Seoul National University) | Park, Sehyeok (Seoul National University) | Xie, Linmao (Seoul National University) | Min, Ki-Bok (Seoul National University) | Rutqvist, Jonny (Lawrence Berkeley National Laboratory) | Rinaldi, Antonio P. (Swiss Federal Institute of Technology)
Abstract Numerical modeling of fractured geothermal reservoir is conducted to describe coupled hydromechanical behavior at Pohang Enhanced Geothermal System (EGS) site. A hydraulic stimulation was conducted in the PX-1 well at the depth of 4,362m in Pohang EGS site from Dec 2016. Stress-induced permeability changes are inferred to have occurred from well head pressure and injection rate versus time curves during the stimulation. A numerical model of Pohang EGS reservoir is built to simulate hydromechanical behavior during the hydraulic stimulation at PX-1 well. The well head pressure and injection rate curves are reproduced considering corresponding permeability changes by effective stress changes and hydroshearing. History in hydromechanical property changes such as permeability during the stimulation is estimated from the modeling results. In addition, a relationship between effective stress and permeability is obtained through model calibration against the well head pressure and injection rate data. For the numerical modeling, TOUGH-FLAC, a simulator for coupled thermal-hydraulic-mechanical processes in geological media, is used. 1. Introduction Pohang Enhanced Geothermal System (EGS) project has been operated in Pohang, South Korea since 2010. The geology consists of sedimentary rock from ground surface to 2.4km deep, and of granodiorite below the depth of 2.4km. Two boreholes, PX-1 and PX-2, are drilled up to 4,217m and 4,348m respectively. Hydraulic stimulations were conducted in PX-2 from Jan. 29 to Feb. 10, 2016, and in PX-1 from Dec 15, 2016 to Jan 11, 2017. In PX-2, 1,970m of water was injected, and the maximum wellhead pressure of 89.2MPa was observed. The total amount of injected water to PX-1 was 2,689m, and maximum wellhead pressure reached 27.7MPa. The main flow path is expected to be one or two major fault zones intersecting PX-1 and PX-2. Hydroshearing on the pre-existing faults is highly likely to have happened at wellhead pressure of around 15MPa during the hydraulic stimulation in PX-1 according to a result interpretation (Park, S. et al., 2017).
- Energy > Renewable > Geothermal > Geothermal Resource (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Renewable > Geothermal > Geothermal Resource for Power Generation > Enhanced Geothermal System (0.80)