Characterization of Crude Oil for Fireflooding Using Thermal Analysis Methods

Abstract

Abstract To study the thermo-oxidative behavior of crude oils, differential thermal analysis and thermogravi-metric instruments were developed that could be used at 1,000 degrees F and 1,000 psig in a flowing atmosphere. Subsequently, 15 crude oils, ranging from 6 to 38 degrees API gravity, were used at pressures of 50, 500, and 1,000 psig. Both nitrogen and air atmospheres were used in the experiments. The results show that crude oils can be grouped into three types according to their thermo-oxidative characteristics. The gravity of the crude oils does not correlate well with these patterns. It is also shown that the dependence of fuel availability on temperature and pressure varies with different crude oils. Furthermore, crude oils generally gain weight in an air atmosphere in relation to the evaporation curve obtained in a nitrogen atmosphere at both low and high temperatures. This shows that the availability of oxygen at low temperatures changes drastically the quality and quantity of available fuel. The heat generated by low-temperature oxidation might be significant in fireflooding. Finally, a qualitative correlation of the results of thermal analysis with those of combustion-tube tests is indicated. Introduction A substantial investigative effort has been made over the years, bob in the laboratory and in the field to understand the mechanisms of fireflooding, and a general understanding of the process now exists. However, the many factors that affect the process and the interrelationships of these factors process and the interrelationships of these factors make the process a complicated one. This also makes it difficult to predict the behavior of combustion by simple means. The linear laboratory combustiontube test appears to be fairly standard in the industry. Even in this type of experimental approach translation of the linear tube-test results to the field is not always possible. Two of the most important factors in the combustion process are fuel deposition and oxidation. Unfortunately, these presently are also the factors about which the least is known. Fuel for the process is usually thought to be the heavy fraction of crude oil held in the pores after the fluid displacement. The rate of advance and the peak temperature of the combustion front depend on the amount of fuel, availability of oxygen, and the rate of fuel oxidation. In fact, fuel deposition and oxidation govern the ability to sustain forward combustion and strongly influence the economics of a combustion project. Attempts have been made to use the thermal analysis methods in connection with forward combustion. In particular, differential thermal analysis (DTA) was used to study the oxidation of crude oil in porous media. DTA is a technique wherein energy changes in a substance are detected and measured as a function of time or temperature. In practice, the temperature of the sample is compared continuously with a reference material temperature. The difference in temperature is recorded. Another thermal analysis method is thermogravimetric analysis (TGA). In this technique, a sample is weighed continuously as it is heated at a constant rate. The resulting curve of weight change vs time or temperature gives the TGA thermogram. The objective of this work was to study the thermo-oxidative behavior of crude oils using both DTA and TGA techniques to gain some insight into the combustion process, especially the fuel deposition and oxidation. At the same time, we hoped to obtain information useful for predicting the thermal behavior of crude oil in the combustion process. Toward this goal DTA and TGA process. Toward this goal DTA and TGA equipment was developed that could be used at 1000 degrees F and 1,000 psig in a flowing atmosphere. Fifteen crude oils in a wide gravity range (6 to 38 degrees API) were analyzed, and the results are reported here. EXPERIMENTAL EQUIPMENT For our purposes, it was necessary in the DTA block to have a porous matrix to hold the oil and provisions for flowing gas through the sample at provisions for flowing gas through the sample at pressures up to 1,000 psi. The DTA block used is pressures up to 1,000 psi. The DTA block used is shown schematically in Fig. 1. SPEJ P. 211