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Evaluation of Porosity and Absolute Permeability

Discuss about the Conventional Enhanced Oil Recovery Processes.

When the porosity is evaluated, the absolute permeability of the model is calculated by inserting the oil at different flowing speeds according to the drop in pressure at different time intervals. Firstly, the oil has been sent through the concerned architecture at a lower flow speed so that the flow remains stable all throughout. The law proposed by Darcy had been utilized for evaluating the absolute permeability and was arranged by plotting the qm/A and DP/L through the linear aggression procedure. By evaluating the absolute permeability, it was found that it had been equivalent to the straight line’ slope that was arranged with the data.

The experiment concerned with the insertion of gas involves the use of air and nitrogen that have been provided to the model. It is found to be saturated with the oil composition. While inserting the gaseous components the pressure was kept at 1.1029 Bar, which had helped in recovering a specific amount of oil with an asymptotic value. After this value has been reached, the gas pressure is increased to 1.2006 Bar and thus the recovery of oil continues successfully. While using the model, most of the oil comes out or is being expelled and the amount of oil recovered also reaches the value or curve arbitrarily close. The procedures were repeated by providing a constant pressure of 1.4015 Bar. This was a successful procedure because a very little amount of oil was left within the model and most of the oil had been recovered comprehensively.

The prices of crude oils and economic growth have largely impacted the enhanced oil recovery projects. The management of EOR projects is successful only when the investors or shareholders are willing to invest on the project and can handle the risks properly. With the beginning of the EOR projects, it is important to manage the economic exposure and furthermore search for the most effective options of investments that are available.

On the other hand, the Improved Oil Recovery or IOR includes the Enhanced Oil Recovery (EOR) where new drilling technologies are introduced to recover the oil from the wells. It also includes management and controlling of the intelligent reservoirs and even monitoring the effectiveness of the reservoirs and wells to ensure that the primary and secondary recovery processes are successful and noteworthy.

By improving the process of oil recovery from the gas and oil fields, it can take almost double the time needed for increasing the level of production. The world needs energy in larger amount and so there shall be more time for introducing new and innovative alternative sources of energy and technologies. Here we can categorize the various EOR techniques into conventional and improved oil recovery.

Conventional enhanced oil recovery processes

The flooding of water is one of the most effective methods of recovering oil used by the companies in US. The production of oil is mainly done with the help of this process and nearly 50 percent has been produced from the reservoirs till present (Lyons, 1996). [1]

Experimental Procedure of Gas Insertion

There are various benefits of water flooding as an oil recovery process including the lower cost of operations, abundant supply of water and experienced staffs to manage the oil fields. The inappropriate mobility or viscosity ratio between the oil and water could though cerate issues like higher saturation of residual oil

The miscible gas injection technique is favorable for reducing the interfacial tension between the oil and the liquid that has been displaced. After the water is flooded, a specific path is created which has allowed the remaining oil to flow out. Due to this, the saturation of residual oil has been reduced and a negligible amount, i.e., 2 percent of the residual oil is found inside reservoirs. The disadvantage of this EOR technique is that the gas that comes out is not thick as the oil, which creates the issue of viscous fingering

The injection of WAG is used to reduce the technical and economic issues related to the injection of gas. It is one the successful EOR techniques because of the insertion of water slugs and sometimes gas concurrently, which names it as SWAG. The gas is usually first or multi contact miscible and when the water is inserted with the gas concurrently, the gas volume reduces significantly. This is a major problem because the reservoir needs to maintain a significant amount of pressure, which becomes less due to the insertion of gas and water simultaneously. The efficiency of oil to move inside the channel also reduces due to the effects of permeability furthermore. 

The WAG flooding was first used by Mobil at the North Pembina oil field in Alberta, Canada during the year 1957 (Christensen et al., 2001; Mirkalaei et al., 2011). This technique of EOR combines the sweep effectiveness of flooding of water with the microscopic displacement effectiveness of gas flooding. It increased the efficiency of the recovery of oil process largely and ensured continuous flow of oil from the oil fields with much ease.

One of the major drawbacks was the decreased mobility of the fluids accumulated inside the well, because of which the permeability effects might create difficulty in recovering significant amount of oil sometimes.

The chemical flooding is another technique where chemicals are added to the water and it can be further influenced by interfacial tension created between the oil and water. The alkalis and surfactants are responsible for the interfacial tension, which also makes the water thick to match up to the oil (polymers). The chemical flooding was used since 1960 [57]. It was seen that earlier people used to add surfactants as surfactants to the polymers for enhancing the thickness of water and recover the oil with much ease [58]. The alkalis, on the other hand where inserted to ensure that the chemicals’ adsorption was reduced. The alkalis were also used to ensure that the chemical adsorption through the rocks could be decreased and t he oil could be recovered from the reservoir [59].

The long chain polymer molecules are added to the water for increasing the thickness of the water, which also reduces the surface tension of the oil and water. The surface tension between the oil and water is reduced along with the saturation of the oil that is present as residues in the reservoir. This increases the efficiency of the process of recovering oil too.

Impact of Crude Oil Prices and Economic Growth on EOR Projects

One of the major aspect of EOR is to reduce the surfactant adsorption, which has been possible by adding alkali to the oil. This keeps the salinity under control and ensures that the IFT is kept to minimum level. The rocks are made wet, which can further reduce the movement and flow of gas through mixing up of alkali and surfactants with the water that has been inserted. The porous spaces are filled with foams as well.

Injection CO2 into oil fields as miscible flooding promotes oil swelling, reduces oil viscosity, increases oil density; it is soluble in water and can extract and vaporize portions of the oil.

Injection of carbon dioxide is prevalent for more than 40 years due to the effectiveness of displacing oil during the EOR process. As the CO2 is not much thick as the crude oil and water, so viscous fingering is produced due to the inappropriate ratio of mobility of oil and water

As the insertion of gas technique suffers from high level of atomic cleanup, it can create proper movement of the oil that has been trapped inside the reservoir. This situation occurs due to the viscous fingering and separation of gravity caused due to the density and thickness of gas along with the heterogeneity of rocks (Lake, 1989). This problem can be overcome by inserting surfactants and mixing it with the gas or SAG, which further creates foam (Kovscek et al., 1993, Rossen, 1996, Farajzadeh et al., 2009).

There are various ways by which the foam produced can influence the recovery of oil when compared with the water alternating gas flooding procedure (Farajzadeh et al., 2010, Andrianov et al., 2011)

It is possible by keeping the displacement process under control through use of gas or foam that increases the thickness of fluids

The highly permeable swept zones can be blocked so that the fluids are easily diverted into the zones that are not swept

The forces and pressure inside the vessels can be reduced by decreasing the interfacial tension through injection of surfactants. The interfacial mass transfer between the oil and gas would manage smooth movement and flow of oil through termination, reducing the thickness and also by distension or enlargement of the vessels (Nobakht et al., 2008). Due to the selective movement or flow of the foam, the flow of fluids in the permeable layers would be hindered, which could allow for lower permeability (Farajzadeh et al., 2012).

Foam is a gaseous form that can be both continuous as well as discontinuous. In the continuous gas foam, only one pathway is present unblocked by lamellae through which the gas can flow whereas the discontinuous gas foam allows for the movement and flow of gas in the path that has been blocked by lamellae (Figure 12).(Rossen, 1996)

It is often experienced that the movement speed of carbon dioxide inside the hydrocarbon reservoir is higher than the crude oil and it creates further issues like gravity override and viscous fingering. To overcome this kind of problem, the gas bubbles should be trapped in the liquid phase as foams before the carbon dioxide is injected. The aqueous foams are not thermodynamically stable, due to which, the foams should  be prepared in bulk amount properly. To conduct the experiment successfully, the Lignosulfonate and Alkyl Polyglucosides (APGs) can be utilized as two effective sustainable foaming agents for enhancing the flood foaming effectiveness and furthermore ensures stability. The stability of the bulk foam could state that the foams had moved in the porous media quite easily and delivered the best value of mobility reduction within the pores filled medium. The polyurethane polymers are used during the production technique by passing through various processing stages to produce the polyurethane foams. During the beginning of the foam production, the raw materials are considered as liquids stored in the large stainless steel containers. A device is attached to that for ensuring that the most appropriate amount of reactive material can be produced. Thus, the foam flooding is considering as much more effective than the water flooding EOR technique. On the other hand, slugs are used along with the high concentration of surfactant solution to improve the stability of foams and furthermore enhanced the effectiveness of the carbon dioxide foam sweep as well, as it has been found from the experiments that are conducted during the oil recovery process.

Overview of Improved Oil Recovery or IOR

The effectiveness of foam usage for the EOR procedure is based on the capability of the foam to reduce gas permeability that can help in trapping the gas inside the porous media. With the presence of gas bubbles, the thickness or viscosity increases, furthermore creates stability during the process of displacement. People have used the foam injection technique to ensure that the sweep is improved through decrease in the mobility of gas, furthermore allowing the gas that is diverted to sweep the hydrocarbons in the areas of low permeability. There are surfactants that are used to reduce the capillary force, which further reduces the interfacial tension between the liquids that are displacing and those being displaced. The surface tension, viscosity and elasticity are considered as important factors contributing to the stability of foams required to displace oil with ease. One of the major problems faced was the impact of oil on the stability of foams, which could not only cause viscosity fingering problems, but also might deteriorate the recovery of oil.

Density is the measurement of mass in terms of volume and thus is also known as mass density. The mass represents the weight of something that is measured per unit volume. The densities of materials differ while there are several cases where the density is measured in terms of the quantity of moles per unit volume and is known as molar density. The density is referred here as the mass density.

The evaluation of resistance of fluid to flow while putting some tensile or shear stress is known as the viscosity. The two different kinds of viscosity are dynamic and kinematic viscosity.

The porosity defines the capacity of the rocks related to the amount of fluids that can be stored. There are pores inside rocks that hold the fluids. The portion of the rocks that do not contain rock grains or any kinds of mineral cement represent the porosity and can be both absolute and effective porosity.

The ratio between the total volume of pores Vpa and wholesome volume or bulk volume Vb is known as absolute porosity.

The absolute permeability is where fluids can enter through a porous medium through the numerous pores that are interconnected in the network. It demonstrates the porosity of the rocks and has been expressed by the law introduced by Darcy (Zolotukhin, 2000).

The relative permeability can describe the permeability where two or more fluids are found inside the pores. 

The saturation of the fluids represents the volumes of pores that are filled by the fluids. As any fluids such as oil can fill the rock pores, water or gas, the content of the pores can be represented as fraction of the pore volume consisting of the specific fluids.

Mobility

The movement of fluids through the materials consisting of pores and how easily it penetrates through the pores is known as mobility.

There can be interfacial tension in various situations including gas/oil, gas/water and even oil or water. The force that holds the surface of the phase and has been measured with the use of dynes/cm is the interfacial tension [2].

The recreation of oil recovery process from the reservoir can help in managing the behavior of the reservoir through the use of this model. The model can be scaled laboratory model or even mathematical model. The mathematical model consists of various partial differential equations, formulas, which can evaluate the physical processes that have been taking place. Various operations are going on within the petroleum reservoirs and are concerned with the management of fluids flow and transfer of mass. Three phases are managed in concurrently including the flow of water, gas and oil. The transfer of mass process occurs between the phases of oil and gas. During the flow of fluids, various forces like gravity, viscous force and capillary force are considered and have been included in the model equations. The geometry and heterogeneity are considered for managing the reservoir fluids and its flow within, which further develop differential equations obtained through the combination of Darcy’ law and differential material balance.

The two-phase flow of the mathematical model holds various equations that show the flow of fluids within the water geology problem. The basic equations and formulas for differentiation help in managing the two stage incompressible flow of fluids inside the pores and are related to the saturation and pressure equations. The two different laws presented by Darcy for the two stages are added together to determine the pressure equation. The total velocity obtained is later substituted to the total addition of the two mass conservative equations. The mass conservation equation considers the fluid saturation at each stage of the process to evaluate the saturation equation.

The experiments were done considering the limestone cores of Edward. The limestone cores are carbonated rocks that have been studied for enhancing the oil recovery process. The liquid carbon dioxide is inserted along with the use of fractured core plugs. The core plugs are fractured through artificial fracturing processes all throughout the length of the core. The liquid carbon dioxide is inserted at a rate of 4 ml/h by opening the three-way valve between the core and the place where the liquids are to be accumulated. By conducting the experiments, the production of oil, differential pressure and absolute pressure are evaluated with the utilization of a web camera.

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