Abstract

Conventionally, air injection has been used for recovery of heavy crude oil in the production field, but studies have shown that depletion of light crude oil in the reservoir leads to abandonment of such wells. Hence, this work studied the kinetics and combustion of light crude oil in-situ the reservoir to understand their potentials for high-pressure air injection (HPAI) enhanced oil recovery (EOR). Advanced thermo-kinetic simulation and Pressure-Volume-Temperature tools (AKTS and PVTsim) were coupled with non-isothermal Differential Scanning Calorimetry (DSC) measurements and Accelerating Rate Calorimeter (ARC) for the studies. The combustion and kinetics of three (3) light crude oils obtained from Offshore of Newfoundland, Canada were precisely described by the methods. It was observed that the crude with the lowest API of 30.214 had the lowest enthalpy change of 10.9 J/g and the highest onset oxidation temperature of 220 oC, while the crude with the highest API gravity of 46.963 had the highest enthalpy of 24.6 J/g and the lowest onset oxidation temperature of 140 oC. Effect of 10% water saturation of one of the crude samples (Sample A) was studied and it was observed that there was increase in the onset oxidation temperature by 40 oC and lowering of the enthalpy change by 9 J/g. These findings provided evidence that the versatile Differential Scanning Calorimetry thermograms when coupled with kinetic simulation technique can yield reliable results with respect to oil recovery with high correlation coefficient (r > 0.9). This reliable information such as onset, peak and endset temperatures with their respective heat flow patterns, could then be used to provide precise thermo-kinetic parameters. Kinetic triplets such as activation energy, pre-exponential and the reaction model necessary for reservoir screening in an air injection EOR process can also be accurately determined. Mine tailings containing high pyrrhotite content were then used as catalyst to study its effect on the onset oxidation temperature of the crude oils using ARC. An amount of 20% tailings in crude oil lowered the average onset oxidation temperature from 148 oC to 116 oC. It also had the widest oxidation temperature range of 63 oC between the onset and endset temperature, as well as the highest pressure drop of 2.4 bar, which signifies high conversion in the crude oil oxidation reaction as well as production of miscible flue gas which favoured enhanced oil recovery process. Products of air combustion products in-situ was studied as an injectant in a light oil Nigerian reservoir using a simulated slim tube experiment and was observed than flue gas products from air oxidation at high temperature and pressure favoured enhanced oil recovery.

1.1 Preamble

Enhanced Oil Recovery (EOR) is a tertiary recovery process which is normally applied after primary and secondary recovery, to mobilize oil trapped in pores by vicious capillary forces. Thermal, chemical, solvent and gases are the most common form of various EOR process (Isco, 2007). Due to the decline of oil reserves caused by the rising oil production, and clamours for environmentally friendly practice in EOR techniques, petroleum engineers are currently driving EOR projects towards more efficient techniques. One of such efficient technique is the Air/Flue gas injection which is motivated by inexpensive source of air as well as environmentally friendly carbon-dioxide sequestration. The motivation for the use of air as an injectant in the EOR project is because of its abundance, availability and low cost. It can simply be supplied by the use of a compressor, with overall project having low initial and operating cost in comparison to other EOR methods (JOGMEC, 2011).

Air for increasing oil recovery from reservoirs dates back to the 1940’s and early 1950’s (Hvizdos et al., 1983) and by the 1960s and 1970, about forty (40) in-situ full field or pilot projects had been undertaken throughout the world with North America topping such projects (Pwaga et al., 2010). This technique, apart from laboratory studies has been implemented in fields such as West Hackberry in Louisiana, Horse Creek North and South Dakota, Zhongyuan and Liaoche oil fields in China, H field in Indonesia, South Bridge in California and other countries such as Romania, United Kingdom, Japan, Canada, India, Argentina, Venezuela have maintained laboratory and field studies too (Sakthikumar et al., 1996; Ren et al., 1999; Mendoza et al., 2011; Niu et al., 2011; Iwata et al., 2001; Xia et al., 2004; Zhu et al., 2001). Air has also been used in heavy oil recovery and enhancement of this technique can lead to significant light oil production (Surguchev et al., 1998).

An alternative to air injection is the flue gas (which contains nitrogen and carbon-dioxide) produced from the combustion of oxygen contained in the air to sweep oil. This EOR technique, when applied to light oil is known as light oil air injection while in heavy oil reservoir, it is called in-situ combustion. (Kuhlman, 2004; Teramoto et al., 2006; Turta et al., 2007; Li et al., 2009).