The Geoscience of In-Situ Combustion and High-Pressure Air Injection

Abstract

Considering the global drive towarrd net-zero carbon emissions in the near future, the need to find clean sources of energy has never been more important. It is estimated that globally there are tens of thousands of depleted and abandoned oil fields that may be adapted to produce green energy. These may be re-cycled with the help of air injection, either from the production of hydrogen, as a direct result of oxidation of oil, or the exploitation of the inherent increase in heat flow and pressure via enhanced geothermal systems. In the past, the use of in-situ combustion (ISC) and high-pressure air injection (HPAI) have experienced many failures, largely due to poor project design and inappropriate reservoir selection. Here, we review data from field applications, experimental studies, and numerical modelling to define the roles of sub-surface sedimentology and petrophysics, structural geology, geomechanics, mineralogy, diagenesis, and petroleum geology on the success of ISC and HPAI. We show how current knowledge can help mitigate project failure via improved project design and initial reservoir selection. Improvements to the design and implementation of ISC and HPAI projects promise to allow the utilisation of the many abandoned oil fields, to produce green energy with the added benefit of the cost-effective, and materials and energy efficient, re-use of existing oil field infrastructure. We conclude that the integration of field data, laboratory experiments, and numerical modelling methods previously studied can be used to help develop ISC and minimize risk of failure.

Overview of Methods for Enhanced Oil Recovery from Conventional and Unconventional Reservoirs

“…The main part of the heat generated in the reservoir (80% or more) remains in the area behind the combustion front and is gradually dissipated into the rocks surrounding the reservoir. This heat has a certain positive effect on the process of displacement from adjacent parts of the reservoir not covered by combustion [60,92].…”

In Situ Combustion: A Comprehensive Review of the Current State of Knowledge

“…More reactions and more oxygen utilization, High mobility ratios. Possible high recovery factor, low air and energy requirements [24,43].…”

“…However, these compounds are undesired as they promote the formation of stable emul-sions with water [2], and compositionally speaking, LTO reactions contribute primarily to the formation of asphaltenes (pentane-insoluble fraction) [58][59][60] and eventually coke. These compounds are highly undesired as they increase the original oil viscosity, boiling range, and density [3,24,54].…”

“…Such benefits make this approach both more environmentally sound and economically viable [16][17][18][19][20][21][22][23]. According to Storey et al [24], ISC can be used to produce more environmentally friendly energy through the in situ production of hydrogen [19,25] and from the naturally high heat flow of ISC via enhanced geothermal systems [26][27][28][29].…”

“…During in situ combustion processes, it is expected that hydrocarbons/heavy oil/ bitumen and the oxygen-enriched injected air react and interact, resulting in inevitable chemical changes due to the chemical reactions involved. As shown in Figure 3, the reaction zones across the reservoir can be categorized into three different temperature ranges: (1) low-temperature reactions (reservoir temperature up to 300 • C; LTO), (2) medium-temperature reactions (300-350 • C; MTO), and (3) high-temperature reactions (350-525 • C; HTO) [24,[47][48][49][50][51]. The three ISC kinetic regimes are briefly summarized in Table 3, and further details are provided in the following subsections.…”