Zonguldak havzası kömürlerinde gaz depolanmasını kontrol eden parametreler

Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 1998Thesis (Ph.D.) -- İstanbul Technical University, Institute of Science and Technology, 1998Dünyada olduğu gibi ülkemizde de giderek artan enerji gereksinimine cevap verebilecek, yeni enerji kaynaklarına yönelik arayışlar yoğun bir biçimde devam etmektedir. Bu konuda sürdürülen araştırma çalışmalarının öncelikli hedefi, var olan kaynakların daha etkin ve verimli kullanımına imkan verecek yeni üretim tekniklerinin geliştirilmesi doğrultusundadır. Bu nedenle fosil yakıtlar ve bunun yanısıra çevre dostu olması nedeniyle özellikle doğal gaz, günümüzde ilgi odağı olmaya devam etmektedir. Son yıllardaki çalışmalar, kömür kökenli doğal gazın da ekonomik olarak kullanımının mümkün olduğunu göstermiştir. İlk olarak neden olduğu grizu patlamalarıyla bilinen ve işletmecilik açısından istenmeyen bu gaz potansiyelinin varlığı, bilimsel çalışmalar sonucu yeni bir boyut kazanmıştır. Ülkemizde bu tür doğal gaz oluşturabilecek özelliklere sahip tek kömür havzası, Zonguldak Havzasıdır. Havza kömürleri, tektonizma, derinlik ve damar özellikleri bakımından üretim açısından bazı dezavantajlara sahip olsalar da, kömürde oluşan ve birikebilen bu gaz ekonomik rezervler sunabilir. Bu çalışmada esas olarak Zonguldak Havzası Karbonifer istifinde bulunan kömür damarlarının, gaz depolama kapasitesileri ve bu kapasiteyi kontrol eden parametrelerin belirlenmesi amaçlanmıştır. Bununla birlikte, kömürlerin temel özellikleri araştırılmış, kömürlerin karakterizasyonuna ve kömürlerin bir gaz ana kayası olarak özellilerinin belirlenmesine yönelik çalışmalar da gerçekleştirilmiştir. Kömürde oluşan gazın gene kömürün kendi bünyesinde birikmesini kontrol eden parametreler, kömürün petrofiziksel özellikleridir. Bu amaçla, yoğunluk, gözeneklilik, ve yüzey alan değerleri farklı analitik yöntemlerle belirlenmiş ve değerlendirilmiştir. Kısa ve elementel analiz, Rock-Eval Piroliz, TOC ölçümleri, ve organik petrografik analiz gibi enstrümental analiz teknikleri ile kömürün diğer özellikleri belirlenmiştir. Kömür örneklerinin belirlenen bu özellikleri, gaz adsorpsiyon ölçümleri ile hesaplanan gözenek hacim ve yüzey alan değerleri ile birlikte değerlendirilmiş ve değişik parametrelerin kömürlerin gaz adsorpsiyon kapasiteleri üzerindeki etkileri incelenmiştir. Hümik kökenli havza kömürleri, yüksek-orta uçuculu bitümlü kömür sınıfında yer almaktadır ve orta-iyi kaliteli bir gaz ana kaya potansiyeline sahiptir. Kömürlerin CO2 gaz adsorpsiyon izotermleri, mikrogözenekli yapılarda izlenenen Tip I izotermini vermektedir. Adsorpsiyon izotermleri, BET, Langmuir ve Dubinin- Raduschkevich izoterm eşitlikleri kullanılarak yorumlanmıştır. Değerlendirmelerin sonucunda tek tabaka hacim, toplam gözenek hacmi ve yüzey alanı değerleri hesaplanmıştır. Kömürlerin adsorplama kapasiteleri VLang hacim değerleri kullanılarak değerlendirilmiştir. Bu değerler 4.7-36.26 cm3/gr arasında değişmektedir. Adsorplama kapasitesini kontrol eden parametreler, özellikle mikrogözeneklilik, olgunluk, maseral bileşimi ve kömürlerin inorganik madde içeriğidir. To meet the increasing energy demand, search for new energy resources has accelerated in the world and Turkey. The primary goal of the search is to reevaluate and more efficiently utilize already existing resources ; hereby, new methods have been developed. Thats why, fossil fuels especially coalbed methane (CBM) have been a focus of interest. During the last decade, studies have clearly shown that coalbed methane can be economically produced and used. Existence of CBM have been associated with coal mine explosion, and this gas which is undesirable during coal mine operation has been put to production in various locations around the world. In Turkey, the Zonguldak hard coal basin is the one and only location where collides contain coal gas. Although it is widely known that Zonguldak basin display major disadvantages due to basin inversion and deformation of the sedimentary fill, it is still possible that CBM occurrences could have economic reserves. The aim of this study has been the determination of the gas storage capacity and the factors influencing the storage capacity of the Carboniferous coal seams in the Zonguldak basin. Moreover, basic features and characterization of coals have been conducted. Additionaly, evaluation of coal seams as gas source rock has been made. Petrophysical characteristics of a given coal are the controlling parameters of gas storage in coals. Therefore, density, porosity, and surface area have been determined and evaluated following different analytical methods. Proximate, elementel, Rock- Eval, pyrolysis, TOC and microscopic analysis results have been evaluated together with determined pore volume, porosity and surface area values in order to find out the interrelations. The Zonguldak basin containing the Carboniferous coal bearing sequence is part of the so-called Istanbul zone which is a Hercinian continental sliver. The Zonguldak basin is comprised of the Paleozoic, Mesozoic, Tertiary, and Quaternary aged sedimentary fill.Generalized stratigraphy of the basin from the base up is basement,coal bearing formations (Alacaağzı, Kozlu, and Karadon), and cover units. At the base of the section platform carbonates of the Vizeen Yılanlı formation overly the basement and is overlain by the Namurien Alacaağzı formation. Alacaağzı formation consists of prodelta fine elastics and some of coal seams at the upper parts. Alacaağzı formation is overlain by the Westphalien A Kozlu formation. In Late Westphalien delta plain environment is superceeded by the coarse elastics of the Karadon formation which consists conglomerate, sandstone, mudstone and coal. The number of coal seams contained in this formation compared to the Kozlu formation are very few. Pre-Cretaceous sedimentary fill have been affected by Hercinian orogeny. While, the whole fill was influeced by Alpine orogeny. So, the coal-bearing sequence of the XVI Zonguldak basin have experienced two major episodes of basin inversion; indicating that folding, faulting and fracture formation are well developed in the coaly units. In this study, a total of 81 samples from three regions namely Armutçuk, Zonguldak, and Amasra have been collected and analysed. The great majority of the samples belong to the coal seams of the Westphalien A Kozlu formation. Akalın, Sulu, çay, Büyükdamar, and Alimolla coal seams are sampled at the Karadon, Kilimli and Kozlu coal mining plants. Sulu, Acılık, Akalın, and Çay seams are sampled at the Asma and Gelik coal mining plants. In addition to samples listed above, core samples from K20K and K20H wells drilled in the Kozlu block are also obtained. Gas generation potential of coals depends not only the stage of coalification but also on the chemical composition of the organic matter (maceral) contained in a given coal. The total organic matter content, type of organic matter and thermal maturity stage are the main factors determining gas generation potential of coals. These main factors also affect the gas adsorption capacity of coals. These parameters have been determined by geochemical, organic geochemical and organic petrographic analyses. Geochemical characteristics of coal are used in coal classification. Proximate and elementel analyses results on the dry-ash free basis indicated that the coals of the Zonguldak basin are high-medium volatile bituminous in rank. This maturity (rank) range covers the gas generation zone. The transformation of the organic matter under influences of temperature and time has been investigated by elemental analysis. H/C and O/C atomic ratios were calculated and plotted on a Van-Krevelen diagram on which the type and thermal maturity evolution of the organic matter can be followed. From the Van-Krevelen diagram it is apparent that the coal samples investigated in this study plot in the humic coal field. These coals with low H/C atomic ratios are gas-prone. Same results are obtained from Rock-Eval pyrolysis of coals producing low HI values on immature to marginally mature samples indicating gas generating potential. The parameters obtained from Rock-Eval pyrolyses are TOC, Sİ, S2, S3, HI, 01 and pyrolysis Tmax. HI and 01 cross plot are used for inferrence of type and maturity of organic matter contained in coal Likewise, Pyrolysis Tmax is used as thermal maturity parameter. Considering that Tmax increses with maturity; pyrolyzed samples have Tmax values between 420 and 474 °C, indicating varying maturity from immature to overmature. Sub-regional evaluation of maturity distribution suggest that Amasra region's coals are the least mature and maturity increases in Armutçuk and Zonguldak regions. Cross-plot of pyrolysis Tmax and vitrinite reflection shows a linear relation. HI vs Tmax plot indicate that coals are vary from marginally mature to mature with respect to gas generation. Petrographic analyses of coals are visiual observations and vitrinite reflectance analysis. Dominant maceral is vitrinite followed by inertinite and liptinite; with these characteristics the coals are typical humic in nature. Maturity of coals from vitrinite reflectance analysis suggest immature to overmature with values between 0.45 % and 1.43 % Ro ; concordant with maturity determined pyrolysis Tmax. This variation in XVH measurements have been used to make inferences about the internal structure and gas storage capacity of coals. Helium (true) density of coals, which have been corrected for mineral matter, range from 1.07 to 1.52 g/cm3. Particle density measurements on a limited number of coal samples have been conducted using mercury porosimeter and values vary from 1.11 to 1.32 g/cm3. Using these density values, open pore volume and porosity values from 0.006-0.149 cm3/g and 0.75-16.54 %, respectively, have been calculated; In volumetric gas adsorption measurements, at low relative pressure values (P/Po= 0.02), micro pore volume are calculated and in gas flow controlled gas adsorption analysis where relative pressure (P/Po=l) total pore volume are calculated without differentiating pore type and/or size. Using mercury porosimeter, pore volume exceeding 300 Â are calculated based on measured volumes at 60-5000 psia pressure values. Using these values, pore volumes percentages have been calculated. Overall total, micro, and macro pore volumes based on different sample sets are 1.10-6.60 %, 0.47-3.03 %, and 1.40-11.94 %, respectively. Gas storage of coal is controlled by pore volume and internal surface area of coal. Here, the gas is either adsorped on the organic (maceral) surface or absorbed in the molecular structures. In this study, gas storage capacity of coals are determined from adsorption isotherms obtained from volumetric and gas flow controlled adsorption methods. Next, from equations, these isotherms have been interpreted. Adsorption isotherms have been obtained by cross-plotting relative pressure (P/Po) values and adsorped gas volume (V). In gas flow controlled methods, when P/Po relative pressure approaches a value of 1, in volumetric method this value is the range 0.001- 0.02. All the isotherms obtained are classified as Type-I isotherms. Isotherms obtained on samples of Acılık coal seam from Asma coal production plant are shown in Figure 1.1. BET, Langmuir and Dubinin-Radushkevich (D-R) isotherm equations have been used in interpreting the adsorption mechanism in Type I isotherm. These model equations are based on different assumption. In this study, all coal samples are subjected to gas flow controlled adsorption measurements and the obtained isotherms are interpreted using Brunauer-Emmet- Teller (BET) and Langmuir equations. The applicability of Langmuir equation to isotherms is tested by P/V versus V graph produced from analysis results. All the XVIU plots show linear trends with high correlation coefficient. The applicability of BET equation is tested by BET C constant and the correlation coefficient of the relation (P/Po, [V-(l-P/Po)]. Some of the analyzed samples show high correlation coefficient of the relation, but low BET C constant. Only for BET C constant values greater than 10, it can safely be assumed that analysis results are within acceptable error limits. Only 29 out of 81 samples have BET C constants values greater than 10. Langmuir model is more powerful than BET method is explaining the isotherms. BET and Langmuir monolayer volume values of gas between are 2.01-13.25 cm3/g and 4.7-36.26 cm /g, respectively. The surface area values for BET and Langmuir are 10.28-71.20 m /g and 25.0-194.89 m 7g,respectively. For a given sample Langmuir surface area values are always higher than that of BET. Analysis conducted according to volumetric method are employed at low relative pressure and that facilitated the use of Dubinin-Radushkevich (D-R) equation, which originally is, to be applicable to isotherms for microporous material. The results obtained are pore volume and internal surface area values corresponding to the microporous system of the samples. Applicability of the D-R equation depends on the correlation of the relation between Log V and Log2( P/Po). Most of the trends of the relation examined in this study suggest a linear relation. The linearity of the D-R plot indicates that adsorption is a continues process in the microporosity. Points falling away at the ending part of the trend as curvature and as deviations from the trend are probably due to variation in the pore size structure and activated diffusion or molecular sieve effects. Based on the results of 22 coal samples micro pore volume (Vmic) varies between 10.22 and 47.75 cm /g and micro pore surface area between 35.21 to 156.82 m2/g. These values are more correlable with Langmuir surface area values than that of BET. Minimum and maximum values of petrophysical parameters of the coals are given in Table 1.1. Depending on the results, we have accepted the V Lang volume values as a gas adsorption capacities of coals. In the last part of this study, variations in gas adsorption capacity have been compared with the geochemical, organic geochemical, organic petrographic, and petrophysical characteristics of coals. As a result it can be said that the gas adsorption increases with increase in fixed carbon, vitrinite, liptinite, and microporosity of a given coal. With increase in maturity, adsorption capacity first decreases then increases. However, ash and volatile matter content and inertinite macerals negatively affect the gas adsorption capacity; capacity decreases. In evaluation of petrophysical properties of coals determined from parameters obtained from analysis, the measurement results must be evaluated together with experimental conditions. Use of different methods and experimental conditions greatly influence the results XIX Table 1. Minimum and maximum values of petrophysical parameters of coals. XX 14 12 -- 10- -5? fi.. 8 -o.e o -d 4 -- Asma-Acılık Seams x X ? x X 3X X E X ? X a X X ? X X « H ?. X H ? X H h 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 P/Po ? AS.AC1L-1 x AS.AC1L-4 B AS.AC1L-2 XAS.AC1L-5 r AS.AC1L-3. AS.AC1L-6 Figure 1.1 CO 2 gas adsorption isotherms of selected coal seams. DoktoraPh.D