Primary and Secondary Oil Recovery

In primary oil recovery from underground reservoirs, the capillary forces described by the Young and Young-Laplace equations are responsible for retaining much of the oil (residual oil) in parts of the pore structure in the rock or sand. It is these same forces that any secondary or enhanced (tertiary) oil-recovery-process strategies are intended to overcome [2,133,421,690,691]. In an oil-bearing reservoir the relative oil and water saturations depend upon the distribution of pore sizes in the rock. The capillary pressure in a pore is 

One generally attempts to reduce the capillary forces restraining the oil and/or alter viscosity of the displacing fluid in order to modify the viscous forces being applied to drive oil out of the pores. The ratio of viscous forces to capillary forces actually correlates well with residual oil saturation and is termed the capillary number. One formulation of the capillary number is, 

Emulsions are commonly produced at well-eads during primary and secondary (waterflood) oil production. For these processes the emulsification is usually not attributed to formation in reservoirs, but rather to formation in, or at the face of, the well-ore itself [693]. However, at least in the case of heavy-il production, laboratory [694] and field [695,696] results suggest that water-in-oil emulsions can be formed in the reservoir itself during water and steamflooding. Energy is needed for emulsification, partly because of the increased surface area that is created in forming small droplets and partly because deformation of large drops is needed before smaller 

Foams can also be produced during primary production because pressure is greater in the reservoir at the locations from which oil is being drained, and lower near and in the well-bore. As oil moves toward a producing well and then into the bottom of the well, the reduced pressure it experiences can cause dissolved gas to be released. When this happens to a light oil, the gas normally separates from the oil. In the case of some heavy oils, however, the gas remains dispersed in the oil as an in situ oil foam [339,698], This is called foamy-oil production, and can be associated with increased primary-oil production compared to what would be expected from non-foamy-oil production. It is thought that the formation of foamy-oil delays the formation of a continuous gas phase (increases the trapped gas saturation) and contributes a natural pressure-maintenance function [339,698], 

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Fifty years have elapsed since the first major surge occurred in the development of the Athabasca oil sands. The main effort has been devoted to the development of the hot water extraction process 13 significant projects utilizing this process are reviewed in this paper. However, many other techniques have also been extensively tested. These are classified into several basic concepts, and the mechanism underlying each is briefly described. A critical review of K. A. Claries theories concerning the flotation of bitumen is presented, and his theories are updated to accommodate the different mechanisms of the primary and secondary oil recovery processes. The relative merits of the mining and in situ approaches are discussed, and an estimate is made of the probable extent of the oil sand development toward the end of this century. 

Primary and secondary oil recovery methods succeed in recovering, on the average, only one-third of the amount of oil originally in place. In view of the vast amounts of residual (non-recoverable with secondary processes) oil, and of the rapidly deteriorating petroleum demand-and-supply situation, development of enhanced oil recovery methods becomes an utter necessity, at least for the next few decades until more permanent energy sources can be developed. 

Viscosity characteristics of oil Reduction of oil viscosity may be achieved by increasing temperature. This can be done by the injection of hot water or steam into the reservoir. This recovery method is usually applied in the case of heavy oils, for which primary and secondary oil recovery is very low (<10%). The viscosity of these oils is above 100 mPa s and may reach values of several thousands and more. Application of steam injection gives rise to oil viscosity values of about 10-50 mPa-s, as shown in Figure 12.11. 

Secondary recovery techniques comprise injection of water in order to displace the oil and gas injection for maintaining the pressure of the reservoir. The cumulative yield of the primary and secondary oil recovery amounts to 38-43% according to Ref [24]. Success of this technique is mainly limited due to unfavorable wetting conditions. Especially in case of heavy oils, its high viscosity inhibits satisfactory yields merely using water for displacement. Due to the small viscosity ratio, the so-called fingering of the water at the water-oil interface is observed reducing the displacement effect. 

Keywords compressibility, primary-, secondary- and enhanced oil-recovery, drive mechanisms (solution gas-, gas cap-, water-drive), secondary gas cap, first production date, build-up period, plateau period, production decline, water cut, Darcy s law, recovery factor, sweep efficiency, by-passing of oil, residual oil, relative permeability, production forecasts, offtake rate, coning, cusping, horizontal wells, reservoir simulation, material balance, rate dependent processes, pre-drilling. 

Mercury from cinnabar ore 225 tons ore/day (95% recovery) (2) 18,0 ft. diam, 8 hearth furnaces Furnaces fired on hearths 3 to 7, inclusive retention time of 1,0 hr, furnaces are oil-fired with low-pressure atomizing air burners all air, both primary and secondary, introduced through the burners draft control by Monel cold-gas fans downstream from mercury condensers. 

The state of the art in chemical oil recovery has been reviewed [1732]. More than two thirds of the original oil remains unrecovered in an oil reservoir after primary and secondary recovery methods have been exhausted. Many chemically based oil-recovery methods have been proposed and tested in the laboratory and field. Indeed, chemical oil-recovery methods offer a real challenge in view of their success in the laboratory and lack of success in the field. The problem lies in the inadequacy of laboratory experiments and the limited knowledge of reservoir characteristics. Field test performances of polymer, alkaline, and micellar flooding methods have been examined for nearly 50 field tests. The oil-recovery performance of micellar floods is the highest, followed by polymer floods. Alkaline floods have been largely unsuccessful. The reasons underlying success or failure are examined in the literature [1732]. 

Even for reservoirs in which asphaltene deposition was not reported previously during the primary and secondary recovery, it was reported that asphaltene deposits were found in the production tubing during carbon dioxide injection enhanced oil recovery projects (18). 

When this pressure drops, it can be built-up again by water flooding. Unfortunately, after these primary and secondary processes, there still remains up to 70% of the oil adsorbed on the porous clays. Consequently, in recent years, there have been tremendous efforts made to develop tertiary oil recovery processes, namely carbon dioxide injection, steam flooding, surfactant flooding and the use of microemulsions. In this latter technique, illustrated in Fig. 1, the aim is to dissolve the oil into the microemulsion, then to displace this slug with a polymer solution, used for mobility control, and finally to recover the oil by water injection ( 1). 

The above constitute the main uses of LE, amounting to millions of pounds yearly. However, none of these uses is for the LE by itself, ie, solely as a liq. Neat NG has been used in shooting oil wells during the secondary recovery of oil. When oil production from a primary well began to lag, four secondary holes were drilled around the primary well so that all the holes, primary and secondary, were in the form of a five spot . The secondary holes were then loaded with neat NG and shot. 

The fundamental phases of petroleum production include (1) the initial exploration required to find heretofore undiscovered oil and gas reservoirs (2) primary and secondary recovery methods, which make use of both naturally occurring (or primary) reservoir energy and the application of secondary energy sources, such as the injection of gas or water and (3) enhanced oil recovery used to increase ultimate oil production beyond that achievable with primary and secondary methods. Enhanced oil recovery (EOR) methods increase the proportion of the reservoir by improving the sweep efficiency, reducing the amount of residual oil in the swept zones (increasing the displacement efficiency), and reducing the viscosity of thick oils. 

Enhanced oil recovery (EOR) methods increase ultimate oil production beyond that achievable with primary and secondary methods. This is accomplished by increasing the proportion of the reservoir affected. EOR methods arc of three broad groups (1) thermal, (2) miscible, and (3) chemical. 

Tertiary or enhanced oil recovery (FOR) incorporates a variety of techniques involving more elaborate injection schemes than employed in secondary recovery. The treatment of EOR-produced emulsions must be approached independently from any primary or secondary production from the same field or reservoir. Standard demulsifiers and treatment methods used during primary and secondary recovery operations may not handle EOR-produced emulsions. 

Solvent extraction is used extensively to recover chemicals from natural products. Solvents are used to extract and concentrate natural oils and products in the bioprocessing industries (nutraceu-tical, food, pharmaceutical, feed, cosmetic, biotechnology) in quantities from grams to metric tons. Biotechnology applications include the recovery of primary and secondary metabolites [4]. Extraction is used to recover vegetable oils and food products. It is used to process a variety of materials including groundnut, mustard seed, soybean, pahn kemal, sunflower, rice bran, copra, cottonseed, and minor oil seeds like neem, mahua, watermelon seed, castor seed, and so on. 

Conventional (primary and secondary) recovery methods recover only a small fraction of the crude oil originally in place in a typical reservoir. The primary and secondary recovery techniques, which include pressure maintenance by gas injection and water flooding for improved recovery, leave approximately two-thirds of the original oil in the reservoir. As the conventional oil production of the United States continues to decline, enhanced oil recovery will play an important role in the utilization of our domestic resources. Conventional methods do not overcome the basic problems of oil being trapped within the rock pores and of the low mobility of the remaining oil. 

Curve Ti of Fig. 24 shows the oil recovery factor obtained in laboratory experiments, and curve Q oil - the additional oil yield per well obtained at Zybza field during this study after repeated commercial-scale steam soak treatments. The results are similar, they were obtained in both cases by steam treatment of specific sections of the producing bed. Practicdly no oil can be extracted by ordinary primary and secondary production methods from microporous, type I, reservoirs. For this reason, the final cumulative ad tional yield attained during the steam cycles of these reservoirs can be considered as their oil recovery coeffficient... 

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