In this study, the kinetics of heavy crude-oil combustion in porous media are reported. Ramped temperature oxidation (RTO) tests with effluent gas analysis are conducted to probe in situ combustion (ISC) reaction kinetics along with isothermal coke formation experiments. The role of oxygen on coke formation reactions (i.e., fuel formation for ISC) is investigated using X-ray photoelectron spectroscopy (XPS) of intermediate reaction products. The XPS data is analyzed along with companion RTO experiments to obtain a simplified multistep reaction scheme. Synthetic cases illustrate the connection between a proposed reaction scheme for oil/matrix pairs and one-dimensional combustion front propagation. Analysis of experimental results illustrate that the reaction scheme is capable of reproducing experimental results including the basic trends in oxygen consumption and carbon oxides production for RTO experiments as a function of heating rate for both good and poor ISC candidates. The combination of XPS and RTO studies indicates that the quality (or reactivity) of coke formed during the process is a function of oxygen presence/absence. Coke formed in the presence of oxygen is significantly more reactive due to additional oxygen functional groups on the coke surface in comparison to coke formed under an inert atmosphere. Additionally, this work extends relatively easy to perform RTO tests as a screening tool for ISC performance.

One method to access unconventional heavy-crude-oil resources as well as residual oil after conventional recovery operations is to apply in-situ combustion (ISC) enhanced oil recovery. ISC oxidizes in place a small fraction of the hydrocarbon, thereby providing heat to reduce oil viscosity and increase reservoir pressure. Both effects serve to enhance recovery. The complex nature of petroleum as a multicomponent mixture and the multistep character of combustion reactions substantially complicate analysis of crude-oil oxidation and the identification of settings where ISC could be successful. In this study, isoconversional analysis of ramped temperature-oxidation (RTO) kinetic data was applied to eight different crude-oil samples. In addition, combustion-tube runs that explore ignition and combustion-front propagation were carried out. By using experimentally determined combustion kinetics of eight crude-oil samples along with combustion-tube results, we show that isoconversional analysis of RTO data is useful to predict combustion-front propagation. Isoconversional analysis also provides new insight into the nature of the reactions occurring during ISC. Additionally, five of the 10 crude-oil/rock systems studied employed a carbonate rock. No system displayed excessive oxygen consumption resulting from carbonate decomposition at combustion temperatures. This result is encouraging as it contributes to widening of the applicability of ISC.

The original publication was missing the corresponding author to reference 7. The correct reference is as follows:(7) Ambalea, A.; Mahinpey, N.; Freitag, N. Thermogravimetric studies on pyrolysis and combustion behavior of a heavy oil and its asphaltenes. Energy Fuels 2006, 20 (2), 560-565.

Summary This paper presents new semilog-straight-line and temperature-derivative methods for interpreting and analyzing sandface-temperature transient data from constant-rate drawdown and buildup tests conducted in infinite-acting reservoirs containing slightly compressible fluid of constant compressibility and viscosity. The procedures are dependent on the analytical solutions accounting for Joule-Thomson (J-T) heating/cooling, adiabatic-fluid expansion, and conduction and convection effects. The development of the analytical solutions is dependent on the fact that the effects of temperature changes on pressure-transient data can be neglected so that the pressure-diffusivity and thermal-energy-balance equations can be decoupled. The analytical solutions are verified by and are found in excellent agreement with the solutions of a commercial nonisothermal reservoir simulator. It is shown that drawdown and buildup sandface-temperature data may exhibit three infinite-acting radial-flow (IARF) periods (represented by semilog equations): one at early times reflecting the adiabatic expansion/compression effects, another at intermediate times reflecting the J-T expansion in the skin zone if skin exists, and the third at late times reflecting J-T expansion effects in the nonskin zone. Performing semilog analyses by use of these IARF regimes gives estimates of permeability of skin and nonskin zones as well as the radius of the skin zone, assuming that the J-T coefficient of the fluid and the viscosity are known. Parameters such as skin-zone permeability and radius are not readily accessible from conventional pressure-transient analysis (PTA) from which only the skin factor and nonskin-zone permeability can be obtained. The applicability of the proposed analysis procedure is demonstrated by considering synthetic and field-test data. The results indicate that the analysis procedure provides reliable estimates of skin-zone and nonskin-zone permeability and skin-zone radius from drawdown or buildup temperature data jointly with pressure data.

This paper presents new semilog-straight line and temperature-derivative methods (similar to pressure-derivative method commonly used in pressure transient analysis) for interpreting and analyzing temperature transient data from constant-rate drawdown and buildup tests conducted in infinite-acting reservoirs containing slightly compressible fluid of constant compressibility and viscosity. The procedures are based on the analytical solutions accounting for Joule-Thomson (J-T) heating/cooling, adiabatic fluid expansion, conduction and convection effects. The development of the analytical solutions is based on the fact that the effects of temperature changes on pressure transient data can be neglected so that the pressure diffusivity and thermal energy balance equations can be decoupled. The analytical solutions are verified by and are found in excellent agreement with the solutions of a commercial non-isothermal reservoir simulator. It is shown that drawdown and buildup sandface temperature data may exhibit three infinite-acting radial flow (IARF) periods (represented by semilog equations); one at early times reflecting the adiabatic expansion/compression effects, second at intermediate times reflecting the J-T expansion in the skin zone if skin exists, and the third one at late times reflecting J-T expansion effects in the nonskin zone. Performing semilog analyses based on these IARF regimes gives estimates of permeability of skin and nonskin zones as well as radius of the skin zone assuming that the J-T coefficient of the fluid and viscosity is known. Parameters such as skin zone permeability and radius are not readily accessible from conventional pressure transient analysis from which only the skin factor and non-skin zone permeability can be obtained. The applicability of the proposed analysis procedure is demonstrated by considering synthetic and field test data. The results indicate that the analysis procedure provides reliable estimates of skin zone and non-skin zone permeabilities and skin zone radius from drawdown or buildup temperature data jointly with pressure data.