İzmir, Gülbahçe, Sığacık körfezlerinde sıcaklık ve akışkan hızı modellemesi
Temperature and flow modelling in İzmir, Gülbahçe and Sığacık bay
Yazar: DUYGU YAĞCI
Danışman: YRD. DOÇ. DR. DOĞA DOĞAN
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Jeofizik Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2015
Konu: Jeofizik Mühendisliği = Geophysics Engineering

Özet:
Jeolojik olarak Alp-Himalaya dağ oluşum kuşağında yer alan Türkiye, genç tektonik dönemde kazanmış olduğu çok kırıklı yapısı ve geçirmiş olduğu volkanik aktiviteler nedeniyle jeotermal kaynaklar yönünden zengin konumdadır. Türkiye' de jeotermal enerji çalışmaları yaklaşık 45 yıl önce MTA Genel Müdürlüğü tarafından başlatılmış ve bugüne kadar yapılan çalışmalarla 190 adet jeotermal alanın varlığı keşfedilmiştir. Bu alanların % 79'unun Batı Anadolu'da olduğu göz önüne alındığında, bölge gerek genişlemeye bağlı olarak incelmiş kabuk yapısı ile gerekse horst-graben sistemleri ve bunları sınırlayan faylarla ilişkili olarak, jeotermal çalışmalar açısından kritik bir öneme sahiptir. Bu tez çalışması kapsamında Batı Anadolu'da Ege Denizi'nde yer alan İzmir, Gülbahçe ve Sığacık körfezlerinde sayısal sıcaklık ve yer altı suyu modellemesi yapılmıştır. Modelleme aşamasında, sismik yansıma kesitlerinden edilen yer içine ait sediman-ana kaya tabaka kalınlıkları ve fay konumları model geometrisi oluşturmada kullanılarak gerçekçi yer içi statik sıcaklık ve akışkan hızı modelleri elde edilmeye çalışılmıştır.
Yer altı akışkan hızı ve sıcaklık modellemesi, bir hesaplamalı akışkanlar dinamiği yazılımı olan ANSYS FLUENT'in 6.3.26 versiyonu ile yapılmış olup model geometrileri GAMBIT 2.3.16 versiyonlu yazılım ile gerçekleştirilmiştir. Sayısal modelleme için kullanılan sıcaklık değerleri, porozite, permeabilite, ısı kapasitesi, viskozite, ısıl genleşme katsayısı, ısıl iletkenlik gibi yer içi parametreleri daha önce bölgede yapılan çalışmalardan derlenip, sismik kesitlerden elde edilen geometrilerle birleştirilerek çalışma bölgesi içerisinde yer alan bölgede karadan deniz tabanına kadar uzanan fayların bölgedeki jeotermal akışkan rejimine etkileri irdelenmiştir.
Sayısal modellemede kullanılmış sismik hatlara ait anlık genlik kesitlerinde, sıvı ya da gaz içeren sedimanlar olduğu düşünülen düşük genlikli alanlar ve yer altı akışkanlarına işaret eden olası bir çamur diapiri tespit edilmiştir (Altan, 2014). Çalışma kapsamında yapılan Darcy hızı modellerinde de bu türden akışkan çıkışları ve/veya girişleri görülmüş olup mevcut sismik kesitlerle karşılaştırılarak modellerin gerçeğe uygunluğu tartışılmıştır. Çalışmanın kara ayağında ise Balçova jeotermal alanı ve Seferihisar Horst'unu içine alan bir bölgeden alınmış bir kesit doğrultusunda, hem uzunluk hem de derinlik açısından geniş ölçekli bir sıcaklık ve Darcy hızı modeli oluşturularak kara ve deniz modelleri birlikte yorumlanmıştır.

Abstract:
Turkey is located in the Alpine-Himalayan orogenic belt geologically. It has many geothermal resources due to fractured structure geolocigal base. That fractured structure  can be considered to have been formed in the young tectonic period. This period is assumed to be a phase of substantial emergence of the past volcanic activities. As a beginning for the innovative energy explorations, geothermal energy studies have been started by Mineral Research & Exploration General Directorate (MTA) in the past decades. In Turkey, geothermal energy consumption and usage can be observed in a widearea of fields.  Geothermal energy is mainly used in thermal tourism,  which includes alternative curing and health tourism, heating applicationsin many residential and industrial buildings, greenhouse heating, industrial mineral (liquid CO2 ) and also as a renewable and environmental friendly energy production methodin electricity production.  MTA have discovered 190 geothermal areas so farwhich are mostly distributed in Aegean part of Anatolia. West Anatolia, which has 79% of these geothermal areas and has crustal thinnig due to the extensional regime, own many horst-graben systems restricted with the faults is under the influence of active volcanism. Therefore, this region has a great importance for the field of geothermal studies.  In this thesis, a numerical static temperature distribution and ground water flow modeling is performed for İzmir, Gülbahçe and Sığacık Bays which are located in the Aegean Sea. In the modeling process, thickness of basin deposits and bedrock, and the fault locations obtained from the shallow seismic reflection profiles are used for a realistic static temperature distribution and flow modeling.
In the last decade, numerical models of coupled fluid and heat flow wee increasingly used to improve the understanding of hydrothermal systems and their natural evolution. Those numerical models of coupled fluid and heat flow wee are especially used for systems in fractured environments. Amongst hundreds of numerical investigations, recently modelled faulted areas include the Rhine Graben Germany, the Basin and Range, USA, the Ashanti belt, Ghana, and the Mc Arthur and Mount Isa basins, Australia. The major outcome of all these studies is that convection induced by thermal buoyant forces is a major mechanism driving hot basinal fluids. Faults play a dominant role in density-driven flow as they control recharge and discharge. Depending on their hydraulic properties, faults can also allow deep fluid circulation within impervious basement and act as fast flow pathways for both solute and energy transport. In pioneering investigations on groundwater flow in fault zones, it is found that the different regimes of heat transfer (i.e. conductive, advective, stable or unstable convective) fall within discrete ranges of permeability contrasts between the fault zone and the surrounding country rock. Furthermore, fault zones can induce convection in neighbouring units where geophysical conditions are, in principle, not favourable for convective flow. Therefore, in a hydrothermal system, multiple heat transport processes are likely to co-exist. 
ANSYS FLUENT 6.3.26 which is computational fluid dynamics software operating Finite Volume Method (FVM) was used for the flow and temperature modeling by implementing the mesh geometries using GAMBIT 2.3.16 software. The finite volume method (FVM) is a common approach used in CFD codes, as it has an advantage in memory usage and solution speed, especially for large problems, high Reynolds number turbulent flows, and source term dominated flows (like combustion). In the finite volume method, the governing partial differential equations (typically the Navier-Stokes equations, the mass and energy conservation equations, and the turbulence equations) are recast in a conservative form, and then solved over discrete control volumes. This discretization guarantees the conservation of fluxes through a particular control volume.
 The modeling parameters such as temperature, porosity, permeability, heat capacity, viscosity, thermal expansion coefficient and thermal conductivity were acquired from the previous researches that were conducted in the same region. These parameters were combined with the sub-surface geometries obtained from the seismic profiles for investigating the effects of the faults extended from the continental area to the sea floor, on the geothermal flow regime.
In the marine part of the study, a numerical static temperature distribution and ground water flow modeling is performed for İzmir, Gülbahçe and Sığacık Bays which are located in the Aegean Sea. The subsurface structures obtained from the seismic reflection data is used for building mesh geometry. Combining seismic reflection study and numerical flow and temperature modelling is the constitutive idea of the thesis due to procure realistic temperature distributions and velocity models.   
Low amplitude values related to sediments probably including geothermal fluid or gas and a structure interpreted as a mud diapir indicating underground outflow were determined from the reflection strength sections. Those kind of inflow/outflow regimes also were encountered in the Darcy velocity models and they were compared with the present seismic reflection sections in order to discuss whether it is compatible with the seismic interpretations.
This research also monitors usable data regarding continental parts of the region.In the continental part of this research, the temperature and Darcy velocity models were executed in order to analyze the sea and continent models together by choosing a large cross-sectional area in terms of length and depth, including Balçova geothermal area and Seferihisar Horst. The Seferihisar–Balçova Geothermal system is located in the Aegean region, western Turkey. The main faults are the İzmir, Cumalı, Tuzla and Doğanbeyparts of the system which can be named as substantial fault spots. These strike-slip and normal faults break into several splays along which natural hot springs form. Considering temperature observations, it can be noticed that venting temperatures range from 30 °C to 78 °C. To monitor the historical progress of the analysis of the systems it can be determined that,geothermal exploration in the Seferihisar–Balçova Geothermal system started in the early 1960s. Technical authorities has moved the progress of explorations with many welling operations, approximately 50 wells have been drilled by the General Directorate of Mineral Research and Exploration of Turkey (MTA) both for developing and monitoring geothermal energy production. Based on the well log data, geophysical and hydrochemical investigations have been carried out over the Seferihisar–Balçova Geothermal system in order to define its major tectonic features and to delineate the possible groundwater flow paths. Meteoric waters from the Seferihisar Horst infiltrate down to 2 km depth or more. After being heated by an unidentified heat source, the hot and less-dense deep waters ascend to the surface along the major faults and fractures and also the cold water descend to the bottom through major faults. To detect the groundwater movements (flow) and static temperature distribution in the area, a two-dimensional numerical model is choosen. Seferihisar Horst model differs from other models in terms of both scale and topography. Another feature of this model is having sea flor and a topographic rise, which is Seferihisar Horst, together. This feature has insured us an opportunity to investigate the topographicaly-driven flow. A topography-driven flow system is one in which ground water flows from higher-elevation recharge areas, where hydraulic head is higher, to lower-elevation discharge areas, where hydraulic head is lower. This type of flow system is commonly encountered in ground-water basins. The main factors that control ground-water flow are basin geometry, shape of the water table, and the distribution of hydraulic properties. A key purpose of the TopoDrive model is to enable the user to investigate how these factors control ground-water flow. In Seferihisar Horst model, it can be seen that the topography-driven flow is the dominant component of the flow. Temperature distribution of the model tend to be conduction. However, it can be recognized in the Darcy velocity model small convective flows  in the thick reservoir layer and especially in the thin alluvium layer.