An experimental investigation of the in-situ combustion behavior of Karamay crude oil

• Extensive measurements of oxidation kinetics of an active in-situ combustion candidate.
• Comparison of the kinetic characteristics of crude oil fractions and whole crude oil.
• The heaviest crude-oil components contribute make a major contribution to combustion.
• Combustion tube results showing firefront propagation.

The Karamay Field (Xinjiang, China) has crude oil that is 11.8° API and is a potential candidate for in-situ combustion (ISC). During ISC, air is injected into a reservoir to oxidize a small portion of the hydrocarbons present thereby generating heat and pressure that enhance recovery. We have conducted a screening study to evaluate the likelihood of the success of ISC in Karamay. Questions of interest for Karamay include the fraction of the crude oil that is converted to fuel, the quantity of particular crude-oil components that become fuel for ISC, and the ability to propagate a combustion front through porous media. To investigate ISC properties of the oil, true boiling point fractions were collected from Karamay crude oil and the kinetics of oxidation of each fraction in porous media were measured using ramped temperature oxidation (RTO) and compared to the whole crude oil. The isoconversional approach is used to interpret the RTO results of each boiling point fraction to obtain the activation energy characteristics of each boiling point fraction.With increasing boiling point and, consequently, molecular weight, the ignition temperature as well as the temperature for the onset of oxidation increases. Fuel availability increased with pseudocomponent density. The 500+°C boiling point fraction presents reaction kinetics most similar to the whole crude oil indicating that the crude-oil components in this fraction contribute the most to fuel production. Reaction kinetics of the whole oil appeared to be favorable for successful propagation of a combustion front. Importantly, this prediction was validated using displacement tests in a 1 m long combustion tube filled with reservoir sands. The Karamay crude oil demonstrated significant in-situ upgrading as a result of ISC. The gravity of the produced oil was 19.3° API. Our results add to the knowledge base of conditions for successful ISC as well as significant upgrading.