Shapour Vossoughi

Profile modification using in situ gelation technology : a review

Abstract Oil production during the primary stage is achieved due to the natural energy stored in the reservoir. Upon depletion of this energy, the production ceases or the oil production rate becomes so small that it will not be economical to operate. At this stage, a large fraction of the initial oil in place is still trapped under the ground. The oil recovery efficiency during the primary stage is within 10% to 30% depending on the nature of the reservoir. This means that more than70% of the initial oil in place is the target for the secondary and/or improved oil recovery techniques. During the secondary recovery stage, some kind of fluid is injected to push the oil from the injection well toward the producer. Water and gases are the most commonly used displacing fluids in this process. Waterflood is the most common practice of secondary oil recovery techniques. Injection of carbon dioxide or other gases is also a common practice to improve oil recovery efficiency. Regardless of the type of the fluid used to displace the oil, the displacing fluid could bypass the oil and early breakthrough could occur. In the case of waterflood, the water/oil ratio could become so high that the process ceases to be economical any more. For injection of CO 2 or other gases, the high gas/oil ratio renders the process uneconomical. This is more dramatic for heterogeneous and layered reservoirs with contrasting permeability variation among the layers. To remedy the above problem, some kind of polymer solution is injected into the reservoir and is allowed to gel under certain conditions. The gel viscosity being much higher than the displacing fluid could impede the flow of displacing fluid through the already flooded regions; therefore, the displacing fluid is bound to find new paths which means additional oil can be displaced. Profile modification based on in situ gelation technology is an already proven economical process for improving oil recovery. There is a variety of gelation systems available in the market for the treatment of the reservoir. Most of the gelation systems in the market are based on cross-linking of polyacrylamide-type polymers by some kind of heavy metal ions such as chromium to produce a three-dimensional gel structure in situ in the reservoir. Recent research efforts at the University of Kansas have produced a new type of bio-polymer which gels without cross-linker. Gelation occurs by reducing the pH of the alkaline solution and the gelation process is reversible. This paper will discuss the in situ gelation techniques based on the commercially available systems and the newly discovered bio-polymer as mentioned above.

Study of the clay effect on crude oil combustion by thermogravimetry and differential scanning calorimetry

Thermogravimetry (TG) and differential scanning calorimetry (DSC) were used to study the effect of sand, silica and kaolinite on crude oil combustion. Three distinct regions, namely distillation and two combustion/cracking regions were observed on all TG curves. Thermogravimetric curves were analyzed using an Arrhenius-type kinetic model and a ratio method to obtain kinetic parameters. Activation energy and reaction order were obtained from this analysis. The reaction order seemed to be insensitive to the presence of granular materials. However, a significant reduction of activation energy was caused by addition of kaolinite to the crude oil, indicating that the kaolinite had a catalytic and surface area effect on crude oil combustion/cracking reactions.ZusammenfassungDie Wirkung von Sand, SiO2 und Kaolinit auf die Verbrennung von Rohöl wird mittels TG und DSC untersucht. Alle TG-Kurven lassen drei unterschiedliche Abschnitte erkennen, die der Destillation und zwei Verbrennungs- bzw. KrackvorgÄngen zuzuordnen sind. Die thermogravimetrischen Kurven wurden unter Verwendung eines kinetischen Modells des Arrhenius-Typs analysiert, wobei die Reaktionsordnung erhalten wurde. Die Reaktionsordnung scheint von körnigen Materialien nicht beeinflusst zu werden. Eine signifikante Verringerung der Aktivierungsenergie wurde durch Zusatz von Kaolinit zum Rohöl erzielt, was darauf hindeutet, dass Kaolinit einen katalytischen und OberflÄcheneffekt auf die Verbrennung bzw. auf Krackreaktionen des Rohöls ausübt.РЕжУМЕтг И Дск БылИ ИспОльжО ВАНы Дль ИжУЧЕНИь ВлИьНИь пЕскА, кРЕМНИ ь И кАОлИНА НА гОРЕНИЕ сыРОИ НЕФтИ. Н А ВсЕх тг-кРИВых НАБлУ ДАлОсь тРИ РАжлИЧНыЕ ОБлАстИ, гл АВНыМ ОБРАжОМ — ОБлАсть пЕР ЕгОНкИ И ДВЕ ОБлАстИ гОРЕНИЕ/кРЕкИНг. тг-кР ИВыЕ БылИ АНАлИжИРОВ АНы НА ОсНОВЕ кИНЕтИЧЕск ОИ МОДЕлИ тИпА АРРЕНИ УсА И ОцЕНЕН пОРьДОк РЕАкцИИ. кАжЕ тсь, ЧтО пОРьДОк РЕАкцИИ Н Е жАтРАгИВАЕтсь пРИс УтстВИЕМ гРАНУлИРОВАННых МАт ЕРИАлОВ. ВМЕстЕ с тЕМ, пРИ ДОБАВлЕНИИ к АОлИНА В сыРУУ НЕФть, НАБлУДАлОсь жНАЧИНЕ льНОЕ пОНИжЕНИЕ ЕНЕР гИИ АктИВАцИИ. ЁтО УкАжыВ АЕт НА тО, ЧтО кАОлИН Вы жыВАЕт кАтАлИтИЧЕскИИ ЁФФЕ кт И ЁФФЕкт плОЩАДИ пОВЕРхНОстИ В РЕАкцИИ гОРЕНИЕ/кРЕ кИНг сыРОИ НЕФтИ.

Kinetics of Crude-Oil Coke Combustion

Coke is a solid or semiliquid material that deposits on the sand-grain surface area and is eventually burned as a fuel during an in-situ combustion process. Its combustion is the main source of energy to sustain the fire front. This study investigates the effects of different variables - such as specific surface area, oxygen partial pressure, and oil content - on the coke combustion by thermogravimetric analysis (TGA). Each variable was varied while the others were kept constant. The TGA and the derivative thermogravimetric (DTG) curves were subjected to kinetic analysis. The rate equation produced indicated that the rate of coke combustion was proportional to the coke content yet to be burned, oxygen partial pressure, and sand-grain specific surface area. The rate constant followed an Arrhenius-type equation for the temperature dependency. The rate equation was tested for the range of specific surface areas of 0.126 to 24.3 m/sup 2//g (615 to 119,000 ft/sup 2//lbm), oil content of 10 to 58 wt%, and oxygen partial pressure of 5 to 50 kPa (0.05 to 0.50 atm). The models validity was tested for various crude oils from different geographical locations in the U.S., Canada, and Latin America.

Catalytic effect of heavy metal oxides on crude oil combustion

Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were applied to crude oil combustion in the presence and absence of metal oxides. It was found that the effect of titanium oxide was similar to that of silica and alumina. Vanadium, nickel, and ferric oxides behaved similarly in enhancing the endothermic reactions. In the presence of a large surface area such as with silica, the surface reactions are predominant and unaffected by the small amount of metal oxide present. Kinetic analysis of the DSC curves revealed that the activation energies and the frequency factors of the hydrocarbon and the coke combustion reactions, estimated for all the metal oxide additives including silica and alumina, followed the same normal compensation trend. The crude oil mixture of 90% ferric oxide was the only exception to this trend.

Flow of non-newtonian fluids in porous media

Publisher Summary This chapter discusses the nature of non-Newtonian fluids that are commonly employed, followed by a look at the nature of the idealized porous media and the geometrical complexity of true porous media. Fluid and porous media interaction, such as adsorption, mechanical entrapment, and inaccessible pore volumes, have direct effect on the flow and are analyzed and quantified. The chapter studies microscopic and macroscopic views of the flow and presents the predictive models available for the study of the non-Newtonian fluid flow through porous media. This includes models based on hydraulic radius concept, friction factor/Reynolds number relationship, and empirical methods. Non-Newtonian fluid flow through porous media has become increasingly important in a wide range of disciplines and industrial segments. Catalytic polymerization process, the injection of polymer and surfactant solutions into petroleum reservoirs to enhance oil recovery, food processing, and fluid flow through riving tissues are examples of the vitality of understanding the non- Newtonian fluid flow through porous structures.

Kinetics of liquid hydrocarbon combustion using the DSC technique

Abstract TGA/DSC techniques were applied to the combustion of crude oil in the presence of solid particles of various specific surface areas. The major physical and chemical transitions observed were classified into three groups, namely distillation, liquid hydrocarbon combustion and coke combustion. This paper deals with the peak associated with the liquid hydrocarbon combustion. Kinetic study revealed that the liquid hydrocarbon combustion peak consisted of two types of combustion reactions which could not be modelled with a single power-law-type kinetic model. Oxygen concentration of the purging gas was varied and its effect on the DSC curve was monitored. It was noticed that at low oxygen concentration, i.e. in the range of 5 to 10%, two distinct peaks emerged. Kinetic analysis of each peak produced a power-law kinetic model for each reaction. The kinetic model was first-order with respect to oxygen partial pressure for both peaks. The order of reaction with respect to the hydrocarbon content was unity for the first peak and 1.5 for the second peak. Optimization of all the data produced a reaction order with respect to the surface area of −0.57 for the first peak and −0.2 for the second peak.

Feasibility Study of the In-Situ Combustion Process Using TGA/DSC Techniques

The influence of reservoir rock on the in-situ combustion process has been recognized by many investigators as an important part of the process. Several experimental studies have shown the effects of reservoir rock on the in-situ combustion process. However, all the available screening criteria neglect this important and decisive criterion. This paper describes how the reservoir rock affects the minimum oil content necessary for the self-sustained combustion, which is introduced as a new criterion for the selection of suitable reservoirs for the process. Differential Scanning Calorimetry (DSC) was employed to determine the heat value of the oil in the presence of the reservoir rock. The minimum temperature required for the total consumption of the fuel was obtained by the use of Thermogravimetric Analysis (TGA) and DSC. The minimum amount of oil necessary to sustain the combustion was calculated from these two parameters and compared with the oil saturation of the reservoir. Reservoirs with oil saturations above this minimum value were considered feasible. In-situ combustion tube experiments performed on actual reservoir rocks obtained from Kansas fields confirmed the validity of the prediction.

TGA/DSC techniques as research tools for the study of the in-situ combustion process

This paper summarizes the recent past and the present research activities and predicts the foreseeable future augmentation in the area of TGA/DSC application in the in-situ combustion process. The types of information obtainable from TGA and DSC curves of crude oil combustion can be summarized as: (a) the major crude oil transitions involved, (b) the effect of clay, (c) the effect of the sand grain specific surface area, (d) kinetic data, and (e) combustion feasibility. Presently, research in our thermal recovery laboratory is directed toward a simultaneous run of the thermogravimetric analyzer and the in-situ combustion tube system. This is achieved by bypassing the TGA controller and controlling the TGA oven by the same minicomputer which is monitoring the tube. Therefore, the temperature of the TGA oven will be brought close to the temperature of a point in the tube from which the gas sampling probe will direct the flowing gas to the TGA sample pan. It is anticipated that TGA curves obtained in this fashion will reveal the actual physical and chemical transitions occurring in the tube and provide some insight into the mechanisms involved. In view of the results published recently, it is concluded that quantitative prediction of the combustion tube test behavior using TGA/DSC technique is possible.

An Experimental and Numerical Investigation of Solvent Injection to Heavy Oil in Fractured Five-Spot Micromodels

Abstract In this work a series of solvent injection experiments was conducted on horizontal glass micromodels at several fixed flow rate conditions. The micromodels were initially saturated with heavy crude oil. The produced oil as a function of injected volume of solvents was measured using image analysis of the continuously provided pictures. In order to investigate the macroscopic behavior of the process in different media, several fractured, with constant width, and nonfractured five-spot micromodels were designed and used. The measured data have also been used for verifying and developing a simulation model that was later used for sensitivity analysis of some parameters that affect oil recovery. The results show that when the fracture spacing increased, the oil recovery decreased. In contrast, as the fracture orientation angle (the angle with the mean flow direction) or solvent viscosity increased, the oil recovery increased. A critical value for the ratio of connate water saturation to the oil volume has been found that, beyond that the solvent injection process, loses its efficiency. The final recovery of a water alternating solvent (WAS) injection process in fractured medium in the presence/absence of connate water saturation was considerably greater than that obtained either by continuous solvent injection or water injection alone. Good agreement was observed between experimental and simulation results when a dual permeability model was used in our simulation.

Prediction of In-Situ Combustion Process Variables By Use of TGA/DSC Techniques and the Effect of Sand-Grain Specific Surface Area on the Process

This paper describes a new technique to predict the parameters that govern the performance of the in-situ combustion process. This prediction is accomplished by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) of the crude-oil combustion. The effect of surface area on the in-situ combustion-tube runs was also investigated.