Fluid Pressure Heterogeneity in Rock Fractures and Its Influence on Injection-induced Earthquake Prediction

( Wei Wu ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2

Fluid injection into a highly heterogeneous fault causes the build-up of localized fluid pressure and initiates the rupture of pressurized fault segment. The rupture front may propagate along the fault subjected to tectonic stress and finally trigger a large earthquake. We carry out a suite of triaxial shear-flow experiments on sawcut fractures in granite to reproduce the injection-induced fracture instability due to heterogeneous fluid pressure distribution. When distilled water is injected at one side of a sawcut fracture in a granite sample subjected to triaxial compression, the pore pressure measured at the other side of the fracture rises at different increasing rate depending on the permeability of the fracture. We find that when the pore pressure is homogeneously distributed in a high-permeability fracture, the fracture instability is mainly due to the near-uniform reduction of effective normal stress. If the fracture permeability is low, the pore pressure amplifies near the injection borehole, and induces fracture rupture propagating in the unpressurized area. The pore pressure can only perturb limited area around the borehole in an extremely low-permeability fracture, and the entire fracture remains stable. The relationship between the seismic moment release and fluid injection volume assumes the uniform distribution of injected fluid in fault, and may not reasonably predict the seismic moment release due to the rupture of highly heterogeneous fault. This study provides a possible explanation of ~800 times unexpected seismic energy released during Pohang earthquake.

수리자극에 의한 지열저류층에서의 유도지진과 단층대의 변형에 관한 입자기반 개별요소법 모델링 연구

윤정석(Jeoung Seok Yoon),아미르 하킴하쉐미(Amir Hakimhashemi),아노 짱(Arno Zang),귄터 찜머만(Gunter Zimmermann) 한국암반공학회 2013 터널과지하공간 Vol.23 No.6

본 수치해석논문에서는 절리와 단층대를 포함한 지열저류층에 수리자극을 가할 시 수반되는 유도지진과 단층대의 변형을 개별요소법을 사용하여 모델링하였다. 수채해석기법은 2차원 입자유동코드를 기반으로 하며 수리역학적 상호작용기법과 미소파괴음의 모멘트텐서 역산알고리즘이 결합되었다. 수치해석의 주요결과로는 시공간적으로 변하는 유도지진의 분포와 규모 그리고 단층대의 변형(파괴 및 전단변위)과 주입유체압력의 시공간적 분포와의 상관관계이다. 첫 번째 수치해석으로부터 절리가 분포하는 지열저류층에서의 수리자극에 의한 유도지진의 분포는 주입유체의 점성에 상당한 영향을 받는 것으로 나타났다. 주입유체의 점성이 낮은 경우 (1cP), 유도지진의 발생범위가 큰 것으로 나타났으며, 주입 후 발생하는 유도지진의 개수와 규모 또한 높게 나타났다. 단층대가 존재하는 지열저류층의 수리자극 모델링의 결과, 주입정의 위치가 단층대와 가까운 경우 작은 주입수 압력분포(<0.1 MPa)로도 단층대의 파괴와 전단변형을 일으킬 수 있는 것으로 나타났다. 본 논문에서 소개한 수치해석기법은 수리자극을 통한 지열저류층 개발 시 유도지진의 분포와 규모를 실제 유체주입작업 전에 예측할 수 있게 함으로써 지열에너지개발 분야에서 유용하게 사용될 수 있을 것으로 기대한다. This numerical study investigates seismicity and fault slip induced by fluid injection in deep geothermal reservoir with pre-existing fractures and fault. Particle Flow Code 2D is used with additionally implemented hydro-mechanical coupled fluid flow algorithm and acoustic emission moment tensor inversion algorithm. The output of the model includes spatio-temporal evolution of induced seismicity (hypocenter locations and magnitudes) and fault deformation (failure and slip) in relation to fluid pressure distribution. The model is applied to a case of fluid injection with constant rates changing in three steps using different fluid characters, i.e. the viscosity, and different injection locations. In fractured reservoir, spatio-temporal distribution of the induced seismicity differs significantly depending on the viscosity of the fracturing fluid. In a fractured reservoir, injection of low viscosity fluid results in larger volume of induced seismicity cloud as the fluid can migrate easily to the reservoir and cause large number and magnitude of induced seismicity in the post-shut-in period. In a faulted reservoir, fault deformation (co-seismic failure and aseismic slip) can occur by a small perturbation of fracturing fluid (<0.1 MPa) can be induced when the injection location is set close to the fault. The presented numerical model technique can practically be used in geothermal industry to predict the induced seismicity pattern and magnitude distribution resulting from hydraulic stimulation of geothermal reservoirs prior to actual injection operation.

Experimental study and analysis on physicochemical properties of coal treated with clean fracturing fluid for coal seam water injection

Gang Zhou,Cunmin Wang,Qi Wang,Yixin Xu,Zhanyi Xing,Baoyong Zhang,Cuicui Xu 한국공업화학회 2022 Journal of Industrial and Engineering Chemistry Vol.108 No.-

In the process of coal seam water injection, the components of different fracturing fluids have differenteffects on coal. To analyze the effect of water injection fracturing fluid on the physical and chemical propertiesof coal, we studied the relationship between guar-based fracturing fluid and cationic clean fracturingfluid (C-VES). Microscopic experiments show that guar-based fracturing fluid has a certain viscosityeffect on coal, while C-VES can adsorb and capture the primary coal dust in coal. FTIR analysis shows thatC-VES has a great change on the content of coal functional groups, and guar-based fracturing fluid haslittle effect on coal. Industrial analysis shows that C-VES can better reduce the ash content of coal andhas a certain impact on the thermal efficiency of coal than guar based fracturing fluid. Combustion characteristicexperiment shows that guar-based fracturing fluid does not affect the combustion effect of coal,and C-VES can expand the exothermic temperature range of coal but has little effect on the main combustionof coal. Molecular dynamics simulation results show that C-VES has the best wetting effect oncoal. This research provides theoretical guidance for dust prevention and improving the use and conversionefficiency of coal.

암반 그라우팅 주입 설계변수가 주입성능에 미치는 영향의 수치해석적 평가

이종원(Jong Won Lee),김형목(Hyung Mok Kim),Mahmoud Yazdani,박의섭(Eui-Seob Park) 한국암반공학회 2017 터널과지하공간 Vol.27 No.5

본 연구에서는 암반 절리 내 점성유체 주입시 주입 설계변수가 주입 성능에 미치는 영향을 평가할 목적으로 UDEC 프로그램을 사용하여 1차원 선형유동 해석을 수행하였다. 주입 설계변수로는 주입 압력, 유체 압축률, 주입재의 항복강도 및 점성도의 시간의존성, 주입 압력에 의한 절리의 역학적 변형을 설정하였으며, 주입재의 침투거리 및 주입 유량을 통해 주입 성능을 평가하였다. 수치해석 결과는 이론해를 통하여 파악한 주입 성능양상과 유사한 결과를 보였다. 주입재의 항복강도 및 점성도의 시간의존성을 고려하지 않을 경우, 주입재의 누적 주입량은 시간의존성을 고려한 해석에 비하여 약 1.2배 크게 평가되었다. 또한, 수리-역학 연계해석결과로부터 주입 압력에 의한 절리의 역학적 변형이 발생하는 경우, 절리 간극이 일정한 수리유동 해석에 비하여 누적주입량이 약 4.4배 늘어나는 결과를 보였다. In this paper, a numerical analysis of one-dimensional viscous fluid flow in a rock joint using UDEC code is performed to evaluate the effect of design parameters on injection performance. We consider injection pressure, fluid compressibility, time dependence of yield strength and viscosity of injected grout fluid, and mechanical deformation of joint as the design parameters, and penetration length and flow rate of injection are investigated as the injection performance. Numerical estimations of penetration length and flow rate were compared to analytical solution and were well comparable with each other. We showed that cumulative injection volume can be over-estimated by 1.2 times than the case that the time-dependent viscosity evolution is not considered. We also carried out a coupled fluid flow and mechanical deformation analysis and demonstrated that injection-induced joint opening may result in the increment of cumulative volume by 4.4 times of that from the flow only analysis in which joint aperture is kept constant.

리저버 탱크의 Die Turning Injection 적용을 위한 Multi-field CAE 해석

이성희,Lee, Sung-Hee 한국금형공학회 2021 한국금형공학회지 Vol.15 No.1

In this study, die turning injection(DTI) mold design for manufacturing reservoir fluid tanks used for cooling in-vehicle batteries, inverters, and motors was conducted based on multi-field CAE. Part design, performance evaluation, and mold design of the reservoir fluid tank was performed. The frequency response characteristics through modal and harmonic response analysis to satisfy the automotive performance test items for the designed part were examined. Analysis of re-melting characteristics and structural analysis of the driving part for designing the rotating die of the DTI mold were performed. Part design was possible when the natural frequency performance value of 32Hz or higher was satisfied through finite element analysis, and the temperature distribution and deformation characteristics of the part after injection molding were found through the first injection molding analysis. In addition, it can be seen that the temperature change of the primary part greatly influences the re-melting characteristics during the secondary injection. The minimum force for driving the turning die of the designed mold was calculated through structural analysis. Hydraulic system design was possible. Finally, a precise and efficient DTI mold design for the reservoir fluid tank was possible through presented multi-field CAE process.

Investigation on Leakage Characteristics of Two Kinds of Injection-type Shaft Seals Using CFD

Sanjar Mamatov,Dongwon Shin,Sang-Shin Park 한국유체기계학회 2020 International journal of fluid machinery and syste Vol.13 No.3

Recently, injection-type shaft seals (non-contact type seals) started replacing their counterparts called mechanical seals (contact-face type seals) in power plant feedwater pumps. Both of these seals have primary function of preventing the fluid inside the pump pressure casing from leaking to outside of the pump. Mechanical seals are reported to fail rapidly and abruptly in especially power plant feedwater pumps because of increased speeds and the feedwater temperatures. If mechanical seals fail, most often the pump must be shut-down immediately and put the pump reliability in question. Hence, the injection-type shaft seals were introduced in order to avoid reliability problems associated with mechanical seals and save maintenance costs of feedwater pumps. Therefore, in this paper we investigated the performance of injection-type shaft seals particularly with labyrinth and plain annuls designs. Research findings show that design parameters such as seal clearance and diameter play an important role in determining the injection-type shaft seal’s leakage, while drain temperature was un-affected by these design parameters.

금형 냉각 최적화를 위한 기체 보조 냉각

임동욱,김지훈,신봉철,Lim, Dong-Wook,Kim, Ji-Hun,Shin, Bong-Cheol 한국금형공학회 2018 한국금형공학회지 Vol.12 No.1

Both injection and injection molding dies have evolved into advanced technology. Product quality is also evolving day after day. Therefore, the conditions of the injection mold and the injection conditions are becoming important. In order to improve the quality of the product, the Hardware part of the mold has developed as an advanced technology, and the Software part has also developed with advanced technology. This study deals with the cooling part, which is part of the hardware. In addition to fluid cooling, which is commonly used in the industry, by using gas cooling identify the phenomena that appear on the surface of the product and the critical point strain of the product to find the optimal cooling. Electronic parts and automobile parts whose surface condition is important, the cooling process is important to such a degree that they are divided with good products and defective products according to the cooling process at the time of injection. By controlling this important cooling and reducing the injection time with additional cooling, the product quality can be increased to the highest production efficiency. In addition, high efficiency can be achieved without additional investment costs. This study was conducted to apply these various advantages in the field.

Effect of Formation of Segmented Fractures Induced by Fluid Injection on Major Design Parameters

Sim Young-Jong(심영종) 한국지반환경공학회 2009 한국지반환경공학회논문집 Vol.10 No.6

유체를 주입하여 암반을 파쇄하는 기술은 지열이나 석유 및 가스 등을 추출하는데 널리 사용되고 있는 방법이다. 본 기술을 적용 시 단일균열이 형성되면 이러한 에너지를 추출하는데 가장 이상적이다. 그러나 이러한 단일균열의 형성은 매우 드문 현상이며 분할된 형태의 균열생성이 흔한 현상이다. 이에 균열간 기계적 상호작용의 영향으로 설계변수에서도 단일균열을 가정하고 적용되었던 값과 차이를 보일 것으로 예상된다. 본 연구에서는 균열이 분할 생성되었을 경우 기계적인 상호작용을 고려할 수 있는 수치해석기법을 기존의 개발된 모델과 연계하여 설계변수인 길이, 균열폭, 그리고 압력을 계산하였다. 그 결과 균열의 형성은 이렇게 유체를 주입하여 암반을 파쇄 시 사용되는 설계변수에 상당한 영향을 끼치는 것으로 나타났다. Rock fracturing technique through fluid injection into the wellbore has been widely used to extract geothermal heat and to enhance oil and gas production. Single fracture formation is ideal for the production. However, it is very difficult to form single fracture formation. Instead, the formation of segmented fracture is a common phenomenon. Therefore, design parameters are expected to be different from those of single fracture because of mechanical interaction between segmented fractures. In this paper, design parameters such as length, aperture, and net pressure are evaluated by using model of segmented fracture in which numerical technique is incorporated to consider mechanical interaction between segments. Results show that the existence of fracture segmentation affects design parameters in fracturing treatment in rock by fluid injection.

가솔린 기관에서 물 분사 시스템 구성을 위한 시뮬레이션 모델 개발 및 검증

박준혁(Junheuk Park),Maike Sophie Gern 한국자동차공학회 2019 한국자동차공학회 부문종합 학술대회 Vol.2019 No.5

Water spray characterization of a multi-hole water injector is investigated by numerical simulation. Two points of spray characteristics validate spray simulation using CFD. The first validation method is geometrical evaluation involving spray penetration and angles. The second one is conducted concerning heat and mass transfer of water spray, especially for evaporation process of water and resultant cooling effect on air flow. The primary purposes of this study are the development of relevant simulation model and evaluation of the effect of water injection. The ANSYS CFX Software is used to simulate the water spray and gas exchange process of the engine. The 8-hole water injector is applied to water injection, and the spray simulation model for the water injection is developed and calibrated by experimental results.

유체 주입을 동반한 절리 암반의 수리-역학 특성 평가에 대한 고찰

김형목(Hyung-Mok Kim),Yves Guglielmi,Jonny Rutqvist,박의섭(Eui-Seob Park) 한국암반공학회 2019 터널과지하공간 Vol.29 No.1

최근의 이산화탄소 심지층 처분, 인공지열저류층 형성 및 발전, 원유회수증진 사업 등에는 고압의 유체를 주입하는 과정이 수반되고 이들 사업의 안전하고 성공적인 수행을 위해서는 대상 부지 절리 암반의 투수 특성 및 주입압에 의한 역학적 변형에 기인한 변화를 정확하게 평가하는 것이 중요하다. 본 고에서는 절리 암반 수리-역학 특성 파악을 위한 해석적 및 실험적 평가 방법에 대해 검토하였다. 먼저 유체 주입 전 절리 암반 초기 투과 특성 및 수리-역학 특성 평가에 고려해야 할 기술요소를 분석하고 현장 시추공실험을 통해 이들 수리-역학 특성을 직접 측정하기 위한 최근의 SIMFIP 실험장치의 특징 및 활용방안에 대해서도 검토하였다. Permeability and its change due to a fluid injection in jointed rock mass is an important factor to be well identified for a safe and successful implementation of Carbon Capture and Sequestration (CCS), Enhanced Geothermal System (EGS) and Enhanced Oil Recovery (EOR) projects which may accompany injection-induced hydromechanical deformation of the rock mass. In this technical report, we first reviewed important issues in evaluating initial permeability using borehole hydraulic tests and numierical approaches for understanding coupled hydromechanical properties of rock mass. Recent SIMFIP testing device to measure these hydromechanical properties directly through in-situ borehole experiments was also reviewed. The technical significance and usefulness of the device for further applications was discussed as well.