Batı Raman petrolünün yerinde yanma kinetiğine basıncın etkisinin alışılagelmiş ve eşdönüşüm yöntemleri ile incelenmesi

Crude oils are often grouped into three categories based on specific gravity range as either; heavy oil (10o – 20o API), intermediate oil (20o – 30o API), or light oils (> 30o API). A fourth classification is the so-called extra heavy oils (<10o). Heavy oils have higher viscosities (> 100 cp) and contain larger molecular weight components. Conventional oils (light oils) consist of only 30 % of the world oil resources and therefore technology and resources must be focused on how to extract the abundant heavy and bitumen resources in the various parts of the world. Current methods for extracting heavy and bitumen resources are usually grouped as thermal and non-thermal methods. For very viscous oils, thermal methods, which employ the use of heat to reduce oil viscosity, are usually preferred. Thermal methods include, steam injection, in situ combustion, and hot water injection. On the other non-thermal methods of oil recovery such as waterflooding, CO2 flooding etc. are employed for less viscous oils. Surface mining is usually employed in bitumen extraction, since there is practically no mobility in bitumen reservoirs and waterflooding is a preferred choice in North Sea area where heavy oils are less viscous. Steam injection, which is by far the most popular of the thermal methods, involves the use of an injection well to introduce steam into the reservoir and the use of a production well to produce the mobilized oil from the effect of the steam. The main problem with steam injection method is heat losses. Heat losses for steam injection occurs in the surface lines used for the transportation of steam, in the wellbore to the surrounding formations and in the reservior to overburden and underburden. In addition, problem of gravity override is experienced in relatively thicker formations. In situ combustion, which has been around for a while, is not as limited as steam injection. It is mainly applied as dry forward combustion, in which dry air is injected to a reservoir to create a hot air sweep within the reservoir, as wet forward combustion in which a water alternating gas process is employed to utilize the heat generated efficiently through the water vapor and the hot air sweep and finally as reverse combustion, where injected air and burning zones move counter currently. The main advantage of the in situ combustion process is the generation of heat in situ within the reservoir and the containment of combustion products within the reservoir. The air required for injection is free and can be found in any environment – onshore or offshore. The in situ combustion process is however complex and difficult to engineer and requires several laboratory studies to acquire kinetic parameters and to formulate appropriate reaction models to understand the burning characteristics of the oil involved during the combustion process. The main objectives of this study is to formulate reaction models for the Bati Raman crude oil, a 12o API heavy oil from the Southeastern part of Turkey, to study pressure effect on the isoconversional kinetic analysis, and finally to predict the suitability of the crude oil to undergo combustion using isoconversional methods. Combustion kinetic studies within the literature usually fall under conventional and isoconversional methods. Conventional in situ combustion kinetic studies done by Tadema (1959), Bousaid and Ramey (1968) and Fassihi (1981) all apply a sort of straight-line approach in their interpretation of kinetic data. In these studies, reactions are grouped and lumped together but in reality, crude oil combustion involves several complex reactions. The isoconversional approach, however, provides model free methods which can by-pass the complex reaction model for activation energy estimation. The isoconversional method also provides screening criteria for determination of good and bad candidates for combustion. Conventional and isoconversional studies, which have been done previously point to three main reactions during in-situ combustion process. These reactions are namely: Low Temperature Oxidation (LTO), Middle Temperature Reactions (MTR) and High Temperature Oxidation (HTO). LTO reactions occur below 300oC (573.15 K) as a result of injected oxygen reaction with oil. It produces water, partially oxygenated compounds and carbon oxides MTR occurs between 300o – 400oC (573.15– 673.15 K) and show the characteristic negative temperature region where oxygen consumption decreases as temperature increases. More coke (carboneous material) deposits on the rock matrix during this reaction period. HTO reactions occur above 400oC (673.15 K) as a result of reaction between injected air and deposited coke. Fuel combustion occurs during this period and it produces carbon dioxide, carbon monoxide and water as its main products. In this study, kinetic experiments were conducted at 100, 150, 200 and 250 psig to study the in situ combustion kinetics of Bati Raman oil. In addition effect of pressure on the isoconversional analysis was investigated. The ramped temperature oxidation method was employed, and the produced gases were analyzed for the oxygen and carbon oxides in the effluent gas composition. A plot of gas composition versus time at all heating rates for all operating pressures give a curve that shows the three regions of the three major reactions that take place during crude oil oxidation namely; LTO, MTR and HTO. Using the gas composition plots at various heating rates, it is observed that peak oxygen consumption increases with increasing heating rate. Conventional methods of kinetic studies employ straight-line approach for kinetic data analysis. Activation energy values are estimated for high temperature oxidation region by Fassihi's method. For this method activation energy values generally decrease with increasing heating rate and increase with increasing pressure. The isoconversional technique which is model-free and deconvolve multi-step reactions naturally is also used in the calculation of activation energy in the high temperature region and compared with those obtained with the Fassihi method. The Fassihi method activation energy values are generally higher than those estimated with the isoconversional method. Pressure effect on activation energy is studied using the isoconversional fingerprints generated at different pressures for consumed oxygen with the isoconversional method. The isoconversional fingerprint comparisons show that increase in pressure has a corresponding activation energy increase in estimated values for Bati Raman crude in HTO region. In addition, reaction models were formulated for all operating pressures. Finally, using the various fingerprints obtained at different pressures, Bati Raman crude oil is viewed as a good candidate for combustion.