Variables in the Centrifugal Testing of Petroleum Displacement b y Detergent
Solutions H. N. DUNNING, LUN HSIAO, AND R. T. JOHANSEN Surface Chemistry Laboratory, Petroleum Experiment Station, Bureau of Mines, Bartlesville, Okla. *
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ONCERTED efforts by industrial and government research laboratories have succeeded in developing new and improved methods of petroleum production. Water flooding, one of these methods, has resulted in more complete recovery of petroleum from many reservoirs that had reached the economic limit of primary production. Extensive research has been conducted on the possibility of improving the efficiency of water flooding by surface active additives. The evaluation of detergents for oil recovery is complicated by the difficulty of simulating field conditions in laboratory experiments. Studies of the literature reveal little agreement concerning the conditions actually existing in petroleum-productive formations or the applicability of laboratory results to field use. Because many petroleum reservoirs have surfaces that are a t least partly hydrophobic, a basic requirement of detergents for oil recovery is the ability to displace petroleum from hydrophobic surfaces. Therefore, a preliminary step in evaluating detergents should be the determination of their detersive efficiency in the petroleum-sand system. The extremely large number of surfactants available necessitated development of a rapid method for determining their efficiency in the petroleum-sand system. B centrifugal method for testing this property of surfactants was described recently (5, 6). As several industrial laboratories have begun to use this test to screen detergent formulations and to study oil-displacement phenomena, the test should be generalized so that the results of various laboratories can be correlated. Accordingly, several variables involved in the test have been investigated. The results of these studies and generalizations based on the experimental data are presented. PETROLEUM S A M P L E S
Devonian periods, respectiveIy, and vary widely in their properties, The ranges of various properties are: carbon residue, 0.6 to 3.0%; density (gram per milliliter at 25"), 0.801 to 0.844; viscosity (centipoises at 2 5 O ) , 2.68 t o 5.70; and interfacial tension (water, dynes per centimeter a t 25'), 16.7 to 22.5. The crude oils were topped a t 50" C. and a t a pressure equivalent to about 20 mm. of mercury to remove the more volatile components. This treatment minimized erratic results caused by evaporation during the determinations. GENERAL EXPERIMENTAL CONDITIONS
Experimental conditions specifically applicable to the separate variables studied and those that deviate from the general conditions are described in the discussion of that particular variable. Thirty-five grams of sand and 2.7 ml. of crude oil were separately measured into each of the centrifuge tubes, agitated, and allowed to remain in contact for 20 hours. Commercial Babcock cream test tubes (Xational Bureau of Standards specifications for ASTM standard method) were used in the tests. The tubes then were filled nearly to the top with 0.1 weight % solutions of the detergent to be tested. Triplicate tests were made on groups of eight, in which one of the tubes contained distilled water as a standard. The tubes were centrifuged for 5 minutes and the amount of oil displaced was recorded. After each centrifuging, the tubes were tilted to about 45' and swirled gently about their axis to release trapped oil drops,. Then the tubes were centrifuged for a 15-minute period, followed by centrifuging periods of 5 minutes each until no more oil mas displaced. An International centrifuge, size 1, Model SB, was operated a t 2000 r.p.m. Under these conditions, the centrifugal force was 770 times gravity and the average pressure difference between the two phases was 19 em. of mercury across the sand samde. The temperature of the centrifuge and -detergent solutions dur'ing operation was 30" f 1' C.
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Detergents. The detergents used in these studies were nonionic polyoxyethylated alkyl phenols (3, 5 ) . The detergent series, each based on an alkyl phenol and containing various mole ratios of ethylene oxide, were furnished.by the Hercules Pomlder Co. (Series I), General Aniline and Film Corp. (Series 11), and Rohm & Haas Co. (Series 111) (6). The Roman numeral represents the series and the Arabic numeral represents R, the mole ratio of ethylene oxid'e to alkyl phenol-for example, 1-4 represents the detergent from Series I having a mole ratio of 4 to 1. Sand Samples. The sand samples consisted of virtually pure quartz Ottawa sand, The surface areas of these samples were calculated from the average results of triplicate sieve analyses with the Hatch-Choate equation according to Dallavalle ( 4 ) . A particle-shape factor of 6.4, suggested for worn particles (C), was chosen after examination of photomicrographs of the sand particles. Ottawa sand (IV), previously designated as "railroad white sand," had a surface area of about 110 sq. cm. per gram, according to early microscopic measurements ( 5 ) . The surface areas of sands 111 and IV also were determined by measurements of photomicrographs prepared in accordance with ASTM recommendations ( I ) . The results of these studies are summarized in Table I.
Table I.
Properties of Sand Sand
Property Mesh size, per inch Limits Average Geometric diameter (av.), microns Surface area, sa. cm. per gram Sieve Proj.
I
I1
I11
IV
80-400 200-270
50-270 80-100
40-140 50- 60
40-200 50- GO
70
180
300
330
280
130
73 85
67 78
...
...
Particle-Size Distribution
U. S.Series Sieve Designation No. Microns 40 420 297 50 60 70 80 100 140 200 270 325 400
Petroleum Samples. Crude-oil samples were obtained from the Oklahoma City field, Oklahoma County, Oklahoma, the Rio Bravo field, Kern County, California, the Bartlesville-Dewey field, Washington County, Oklahoma, and the Bradford field, McKean County, Pennsylvania. These crude oils are produced from formations of the Ordovician, Miocene, Pennsylvanian, and 2147
250
210 177 149 105 74 53 44 37
