Experimental Study of Effect of Injection Waters on Cores from Citronelle Field, Mobile County, Alabama

Abstract

Low-temperature hydrothermal flow-through experiments were conducted to model mineral reactions likely to be induced by waterflood-enhanced oil recovery in the sandstone of the Rodessa Formation in the Citronelle field, Mobile County, Alabama. Six flow-through experiments were conducted at 110°C and 300 bars pressure using a 0.5 mL/min fluid-flow rate, various injection solution compositions, and uncleaned or cleaned disaggregated drill-core samples of sand 36, Rodessa Formation. Dissolution of sandstone framework and authigenic mineral constituents increased sample permeability, which was shown to be greatest near injection wells where dissolution rates are highest. Injection of potassium chloride solutions prompted rapid growth of authigenic illite in sand 36, probably through the interaction of K+ with feldspar and/or kaolinite. Substantial kaolinite migration was noted and is postulated to be a potential source of reservoir damage, particularly around injection wells. Both silica and calcium carbonate precipitation were documented in most of the experiments. Differences in the mobilities of these substances in the pH range of 3.5 to 6.5 lead to the interpretation that silica fouling damage should primarily affect injection wells, and that calcit cement damage should be largely concentrated around production wells. These experimental observations provide possible explanations for observed increases and decreases in oil production observed in the Citronelle field as the result of the waterflood program used there since 1961. It appears that flow-through experiments must use a high sample surface area or extend for a long duration to accurately model potential mineral reactions. Conventional high-temperature permeameter tests typically do not meet these requirements.