Changing Casing-Design of New Geothermal Wells in Western Anatolia for Adapting to the Changes in Reservoir Conditions

The traditional casing-design of geothermal wells in Western Turkey is no longer cost-effective and shortening wells’ production lifetime. The current reservoir conditions are much different from their initial values. Significant reduction of reservoir pressure and NCG (Noncondensable Gases) content have been observed in many geothermal fields in Western Turkey due to the construction of oversized power plants, aggressive production, and lack of unitized reservoir management. Thus, there is a need to adapt the casing-design of new production wells for the recent reservoir dynamics. A case study from the Alaşehir field, Western Turkey, is presented in this study. The proposed casing-design increases the performance and production lifetime of the artesian wells. It also enables the operators to use ESPs (Electrical Submersible Pumps) and LSPs (Line Shaft Pumps) with a large diameter for delivering large flowrates. With the new casingdesign, we also aim to prevent casing-collapse due to poor cementing job between 95/8” and 133/8” casings. A set of codes written in Python was used to construct the new casing-design. The effect of the proposed design on the performance of artesian wells is studied using a wellbore simulation program, an academic version of PIPESIM. ESPs are proposed for the new and traditional casing program in the field. The proposed design will give a good insight into the development of the depleted geothermal reservoirs

The Gas Hydrate Potential of the Eastern Mediterranean Basin

Gas hydrate exploration studies have increased substantially since last decade. Gas hydrate reservoirs are commonly found in the marine environment and permafrost. Studies related to natural gas hydrates in the Mediterranean Basin are rare compared to those released on the continental margins of the United States of America, Japan, India, China and Korea. This study provides an evaluation of the gas hydrate potential of the Mediterranean Basin using available literature data such as scientific drilling data (Ocean Drilling Program Leg 160 and Leg 161), sediment data, geothermal data, geochemical data, gas seepage data, mud volcano data etc., It is shown that there is a high producible gas hydrate potential (~ 98.16 standard trillion cubic meter) in the Mediterranean Basin. The Eastern Mediterranean basins have the highest gas hydrate potential due to its high amount of source gas potential and lower geothermal gradient compared to those in the Western Mediterranean.Publisher's Versio

Karadeniz gaz hidratlarının analiz edilmesi.

In this study, it was estimated that 71.8 standard tcm of methane can be available in the Black Sea gas hydrates. However, only 13.6 tcm of this amount was calculated as energy sources. With HydrateResSim simulator, gas production potentials from a hypothetical Class 1 hydrate in the Black Sea conditions by depressurization and depressurization with wellbore heating were simulated. Wellbore heating might be necessary to avoid hydrate reformation along the wellbore during production. For comparison with the data of Class 1 hydrate simulations, hypothetical Class 3 hydrate simulations by depressurization with and without wellbore heating were conducted by HydrateResSim. Experimental set-up for gas production from the Black gas hydrates by depressurization was designed according to the results of HydrateResSim. HEP.m code was written with Matlab to predict hydrate properties. This code was integrated with other codes written to calculate gas compositional change (HEPComp.m) during hydrate formation of gas mixtures, the amount of gas and water to obtain target saturations in experimental studies of hydrate in sediments inside high pressure reactors (SM.m and SMmix.m). BSR.m code was written to predict gas composition near the bottom simulating reflectance in marine sediments. These codes were tested and compared with literature experimental, numerical data, and other software, consistent results were obtained. The Black Sea sediments were investigated and it was observed that clay content is high and turbidites include fine silty sand and sandy silt. However, there might be thin coarse sand sections that might be good hydrate reservoirs for gas production. Ph.D. - Doctoral Progra

Şeyl örneklerinin adsorpsiyon kapasitelerinin ve davranışlarının deneysel olarak analiz edilmesi.

In recent years, unconventional reserves such as shale gas reservoirs have become a major alternative source of energy in the world. It is known that Turkey has shale gas potentials especially in the Southeastern and Thrace region. In shale gas reservoirs, significant amounts of natural gas exist as conventional “free” gas in porous spaces as well as “adsorbed” gas on shale matrix. Understanding adsorption capacities and behaviors of shale gas reservoirs may help exploitation and resource evaluation. In this study, experimental adsorption measurements for shale samples obtained from different shale gas reservoirs in Turkey were conducted at various pressures and temperatures by using pure methane and pure carbon dioxide. It was shown that the effects of temperature and pressure on adsorption are very important. Matlab programs for Ono-Kondo monolayer model, Ono-Kondo three layer model and Ono-Kondo model for binary mixtures of methane and carbon dioxide were written in this study. By using Langmuir model and Matlab programs for Ono-Kondo models, experimental adsorption results were evaluated and adsorption isotherms were constructed. The advantages and disadvantages of these models were compared. It was concluded that Ono-Kondo monolayer model is thoroughly capable to fit adsorption isotherms of shale samples. By using Ono-Kondo monolayer model data, absolute adsorption values were calculated for all adsorption experiments. By conducting carbon dioxide adsorption experiments on shale samples in this study, it was shown that carbon dioxide might be stored in depleted shale gas reservoirs. In this study, initial shale gas-in place equation that uses Langmuir model were modified for Ono-Kondo monolayer model, and then initial-gas in place calculations for unit weight of shale deposits were done. It was shown that shale gas-in place equation proposed in this study is a good alternative for most accurate shale gas-in place calculations.M.S. - Master of Scienc

Design of Electrical Submersible Pump system in geothermal wells: A case study from West Anatolia, Turkey

Geothermal is defined as one of the renewable and sustainable energy sources. The sustainability of geothermal wells is highly dependent on the pressure drive mechanism and non-condensable gas (NCG) content of the produced geothermal fluid. Pressure decline and decline of non-condensable gases are commonly observed in geothermal production wells, which is unfavorable for wells’ lifetime. Electrical Submersible Pumps (ESP) are one of the solutions for extending the lifetime of geothermal wells. In this study, the application of ESP in a geothermal well was designed and simulated. The case study well is located in one of the most exploited geothermal fields in Western Turkey: the Alasehir geothermal field. ESP design is performed by using the codes constructed in PYTHON in this study. The sensitivity of production profiles of the well is simulated by using a wellbore simulation program called WELBOR. Sensitivity studies are conducted for different sizes of production tubing (5, 6, 65/8, and 7 inches), setting depths (500, 600, 700 m), and flow rates (85, 150, 180, 250, and 275 ton/hour). The optimum ESP design conditions are determined by considering pump consumption, flashing depth, wellhead flowing pressure, and production rate. Finally, it was found that ESP design will increase the production rate of the case study well by 165 tons/hour. Furthermore, the proposed ESP will make a profit for at least 8 months, according to the economic analysis in this study.Publisher's Versio

The effect of gas production from deeper conventional gas reservoirs on shallower gas hydrate layer stability: A case study in the conditions of the Sakarya gas field, Western Black Sea

Gas hydrate deposits are generally found in the shallow deepwater regions where continuous permafrost exists. The presence of water, methane and thermodynamic conditions (low temperature and high pressure) is critical for gas hydrate accumulation. Disturbing thermodynamic conditions such as depressurizing and thermal treatment are the primary processes for gas hydrate dissociation. In this study, we investigate the stability of a shallow depth gas hydrate layer in the conditions of conventional gas production from a newly discovered deep gas field, Sakarya gas field, Western Black Sea. The study focuses on thermal conduction generated by conventional gas production across the wellbore profile along the gas hydrate section. The study includes wellbore simulations using the academic version of PIPESIM to obtain temperature and pressure profiles across the wellbore and numerical simulations for thermal transition for various cases in the hydrate zone using TOUGH + HYDRATE v.1.5 (T + H). The temperature elevation in the hydrate zone was found to change between 19 K and 25 K. The critical temperature elevation for hydrate dissociation and hydrate dissociation front were determined using the simulations, which might cause wellbore stability problems in the long term. We increase the impact of the study by suggesting appropriate solutions to minimize the adverse effects of production from the hot and deep conventional gas on gas hydrate stability found at shallower depths.Publisher's Versio

Numerical simulations for short-term depressurization production test of two gas hydrate sections in the Black Sea

Gas hydrates are considered as a promising energy source and the Black Sea has a high potential of gas hydrates. The Danube Delta of the Black Sea is the most well-known prospect in the Black Sea after many geological and geophysical studies such as bottom-simulation reflectors (BSR) and electromagnetic surveys. In this study, gas production simulations from two gas hydrate layers (6 m thick hydrate layer at 60 mbsf and 30 m-thick hydrate layer at 140 mbsf above BSR at 350 mbsf) at the same locations with approximately 50% hydrate saturation in the Danube Fan of the Black Sea were run with depressurization method separately at 2 MPa, 3 MPa, 4 MPa, 5 MPa, and 6 MPa by using HydrateResSim numerical simulators. Moreover, different production tests strategies were suggested in this region