Laboratory Studies On Alkaline Waterflooding

Abstract

Campbell, Thomas C. and Krumrine, Paul H., Members SPE-AIME, PQ Corp., Research and Development Center PQ Corp., Research and Development Center Copyright 1979, American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Abstract This paper describes the results obtained from laboratory tests performed to compare the relative efficiency of sodium orthosilicate versus sodium hydroxide on residual oil recovery. These tests provide supplementary data for an alkaline waterflooding field test. The optimum concentrations of alkali and sodium chloride, used for oil displacement studies, were determined by measuring interfacial tension values of the crude oil in contact with alkaline solutions, which were prepared from soft saline water or from synthetic reservoir brine. Data, obtained from oil displacement studies in Berea sandstone cores, have shown that dilute sodium orthosilicate solutions can recovery significantly higher amounts of residual oil than dilute sodium hydroxide solutions. The crude oil sample used in these studies was taken from the Lower Main Zone of the Huntington Beach Field in California. The differences in recovery efficiency between sodium orthosilicate and sodium hydroxide may be partially explained on the basis of increased hardness ion tolerance, greater surface activity at the oil/water interface, more favorable coalescence behavior, changes in rock wettability and decreases in surfactant adsorption. Introduction A field trial of alkaline waterflooding as an enhanced oil recovery system is in progress in the Huntington Beach Field in California. The Huntington Beach Field trial is being performed by Aminoil-USA, Inc. and is supported in part by grants from the Department of Energy. The laboratory studies summarized in this paper were undertaken to provide additional data to Aminoil on the relative recovery efficiencies of different alkaline chemicals, sodium orthosilicate versus sodium hydroxide, for crude oil from the reservoir. A considerable number of laboratory oil displacement studies have been made by R.M. Weinbrandt of Aminoil-USA using preserved core material from the Lower Main Zone of the Huntington Beach Field, produced crude oil and produced reservoir brine. These produced crude oil and produced reservoir brine. These tests have been run at reservoir temperature in plastic core bodies, and have been designed to attempt plastic core bodies, and have been designed to attempt to optimize the concentrations and slug sizes to be used in the field trial. The tests were run only with various concentrations of sodium orthosilicate, since only a limited amount of reservoir core material was available. Based on these results, the preflush of 0.75% sodium chloride will be injected for 0.35–0.40 pore volumes. Depending upon the behavior of the reservoir, 0.40–0.50 pore volume of 0.15% sodium orthosilicate in 0.75% sodium chloride will be injected as the alkaline slug. A postflush of 0.25–0.30 pore volumes of 0.75% sodium chloride solution is planned, to be followed by injection of produced brine until the test is completed. The produced brine until the test is completed. The injection of sodium orthosilicate solution should commence in August or September of 1979. In order to substantiate for Aminoil that sodium orthosilicate would be more effective than sodium hydroxide, the experiments described in this paper were performed with Berea cores using crude oil supplied by Aminoil. EXPERIMENTAL PROCEDURES The oil recovery experiments were performed using Berea sandstone cores. The Berea cores were 5.1 cm in diameter by 61 cm long cylindrical cores with an air permeability of 150–250 md. These were fitted with steel end-caps and encapsulated in epoxy resin reinforced with fiberglass cloth. In a typical experimental run with the Berea cores, the core was evacuated to a pressure of about 0.3 kPa, then filled with simulated brine from a weighed cylinder co determine the pore volume. The brine was displaced by crude oil at reservoir temperature until no more brine was produced. The crude oil was next displaced by flooding with brine until no more oil was produced. The alkaline flooding procedure was started at this point. procedure was started at this point.