Improved In-Situ Combustion Performance With Metallic Salt Additives

Abstract

Abstract In-situ combustion is an effective thermal recovery process. A part of the oil is burned in-situ, heat is generated, oil viscosity decreases, and larger oil recovery results. Thus, a key mechanism is effective oxidation of a small fraction of the oil in place to generate heat and pressure. Common, water-soluble metallic salts are known to play an important role as a catalyst for some combinations of crude oil/brine/solid matrix. Metallic additives enhance oxidation and cracking of hydrocarbons and thereby affect the nature and the amount of fuel formed. The mechanism of the catalytic effect is, as of yet, unknown. This paper describes an experimental study combining tube runs that gauge combustion performance and ramped temperature oxidation tests that measure the kinetics of combustion. We propose cation exchange of metallic salts with clay as a mechanism to create activated sites that enhance combustion reactions between oil and oxygen. Sand and clay surfaces are examined with scanning electron microscopy for evidence of cation exchange and alteration of surface properties by metallic salts. The oils studied are heavy and light oil from Cymric (Kern, Co., CA). Effluent gas analysis is conducted and temperature profiles are measured. Additive improved performance in all cases including lower activation energy, greater oxygen consumption, lower temperature threshold, and more complete oxidation. In tube runs, Cymric light oil (34 °API) did not exhibit sustainable combustion, but gave sustained combustion with the addition of iron nitrate. Thus, metallic additives have potential to expand the range of candidate reservoirs for in-situ combustion.