Sodium hydroxide solution treatment on sandstone cores

Abstract

This research was performed to study the effect of sodium hydroxide solution on the sandstone core samples and to develop a method whereby the permeability of the samples could be increased by the injection of sodium hydroxide solution. This work should provide the first step in developing a technique that can be used in the stimulation of oil and gas wells. A series of tests was conducted in which sodium hydroxide solution with concentrations ranging from 0.25 N to 2.00 N was injected into a number of Berea sandstone cores. The tests were conducted at toom temperature and at 180(DEGREES)F. In some cases the core sample were damaged by the injection of fresh water which resulted in a marked reduction in the permeability of the cores prior to the injection of sodium hydroxide solution. Based on laboratory testing with measurements of uniaxial compressive strength, SEM examination and X-ray analysis, it was found that sodium hydroxide interacted with sandstone to promote (1) partial dissolution of the sandstone minerals; (2) sandstone weight loss; (3) increased porosity; (4) weakening of the sandstone cores; and (5) changes in permeability. The interaction increased with increasing temperature and increasing sodium hydroxide concentration. More active interaction was also observed when the sodium hydroxide treatment was applied to the damaged samples. At a temperature of 180(DEGREES)F, the permeability of the damaged core samples was increased by the injection of sodium hydroxide solution. However, at concentrations higher than 1.00 N, the degree of increase in permeability was not as large even though the sandstone weight loss and the increase in porosity did increase. It was observed that strong concentrations of sodium hydroxide solution dissolved the calcite which is the cementing material of the sandstone and released insoluble precipitate of sodium carbonate. This resulted in a smaller increase in permeability due to the plugging action of the precipitate. It was noted that some of the precipitate could be removed effectively by the simultaneous injection of Kerosene and sodium hydroxide solution. In this test, sodium hydroxide solution with different concentrations was injected with kerosene into the damaged samples at 180(DEGREES)F and the permeability was increased not only above the permeability to distilled water but above the initial permeability to 10 wt% NaCl solution.