To increase oil recovery

There are two principal mechanisms of enhanced oil recovery increasing volumetric sweep efficiency of the injected fluid and increasing oil displacement efficiency by the injected fluid. In both, chemicals are used to modify the properties of an injected fluid whether water, steam, a miscible gas such as CO2 or natural gas, or an immiscible gas, usually nitrogen. Poor reservoir volumetric sweep efficiency is the greatest obstacle to increasing oil recovery (9). 

A cosolvent used as a miscible additive to CO2 changed the properties of the supercritical gas phase. The addition of a cosolvent resulted in increased viscosity and density of the gas mixture and enhanced extraction of the oil compounds into the C02-rich phase. Gas phase properties were measured in an equilibrium cell with a capillary viscometer and a high-pressure densitometer. Cosolvent miscibility with CO2, brine solubility, cosolvent volatility, and relative quantity of the cosolvent partitioning into the oil phase are factors that must be considered for the successful application of cosolvents. The results indicate that lower-molecular-weight additives, such as propane, are the most effective cosolvents to increase oil recovery [1472]. 

This study investigates the retention behavior of dilute polymer solutions in oil sands. Results indicate that the presence of a large amount of fines and/or a variety of minerals in the sand may result in high adsorption and retention causing excessive loss of polymer and high injection pressures. Injection of a surfactant with the polymer leads to increased oil recoveries because the dilute polymer may selectively adsorb on mineral grain surfaces leaving the surfactant to act at liquid/iiquid contacts. 

Heating the seed to increase oil recovery. This was first interpreted as denat-uration, making the protein matrix brittle to surrender the oil on pressing. Later, it was recognized that concurrent inactivation of enzymes also arrests development of various types of degradations. 

Sandiford, B.B. Laboratory and field studies of well floods using polymer solutions to increase oil recoveries. Pet. Trans. AIME 1964,231, 917-929. 

In one of the experiments the direction of oil displacement was therefore reversed in order to increase oil recovery from the zone of steaming. It was done at the end of the sixth cycle of steam treatment carried out at a temperature of 125°C. By this method, additional oil yield of 12.3% was produced. This oil, which came from the far end of the bed model, away from the line of steam injection, could not be produced in earlier experiments using ordinary direction of steam injection. The results of this experiment were confrrmed quite well by oil field practice. 

The injection of CO2 into the earth s crust is already being undertaken by various oil companies. Since 1996, the Norwegian oil company Statoil has separated more than 1 million tons of CO2 annually from natural gas and pumped it into a saltwater aquifer beneath the floor of the North Sea. In western Canada a group of oil companies has injected CO2 from a North Dakota synthetic fuels plant into oil fields in an effort to increase oil recovery. The oil companies expect to store 22 million tons of CO2 there and to produce 130 million barrels of oil over the next 20 years. 

Sandiford, B.B., Laboratory and Field Studies of Waterfloods Using Polymer Solutions to Increase Oil Recovery., J. Pet. Technol., 16(8) 917-922 (1969). 

Background. Surfactants have been introduced into oil reservoirs to increase oil recovery, minimize adverse mobUity ratios, clean... 

Example 5.7—Polymer Flood in a Linear Reservoir Originally at Intensdtial (Immobile) Water Saturation. The potential of using polymer-augmented waterflooding to increase oil recovery from a uniform reservoir must be evaluated. For the purposes of this example, consider a linear reservoir segment that is 500 ft wide and 20 ft Ihiek. Production and injection wells are 1,000 ft apart. Properties of the reservoir rock and fluids, summarized in Table 5.19, are identical to those used in Example 3.1. Injection rate is constant at 200 B/D. Relative permeability relationships are =0.8(1.(5.66)... 

The unit had been under waterflood since the late 1960 s, and the flood had been successful in spite of an unfavorable mobility ratio of approximately 8.0 (based on kyy at ROS). A polymer flood was initiated in 1985 to increase oil recovery. Ten inverted nine-spot patterns covering about 1,685 acres were used. 

The favorable response presumably resulted from the sealing of fractures with the gel and subsequent diversion of injected water into previously unswept zones. Sydansk and Smith concluded that the gel system could be used in fractured reservoirs to reduce WOR s and to increase oil recovery and that the system was cost-effective. 

Sandiford, B. B. Laboratory and Field Studies of Water Floods Using Polymer Solutions to Increase Oil Recoveries , ], Pet. Tech. (Aug., 1964)917-922,... 

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