Improved Residual Light Oil Recovery by Air Injection (LTO Process)

Abstract

A new air injection technique, low temperature oxidation (LTO) process, is described. Improved oil recovery from deep, light oil reservoirs is achieved by removing the oxygen in the injected air by LTO reactions with the residual oil in the reservoir. The product of the LTO reactions is a "flue gas," which displaces the oil. Preliminary results of LTO reaction kinetics and oil recovery have been obtained using four North Sea light oils. The paper also contains some discussion of the safety issues related to air injection offshore. Introduction Gas injection into light oil reservoirs is a proven improved oil recovery IOR technique. The IOR potential for gas injection in the United Kingdom Continental Shelf (UKCS) has been estimated at 1.4 bSTB(1). However, the application of gas injection is limited by gas availability and cost, particularly for many mature fields, with the prospect of abandonment unless economic methods can be developed to extend the field life. Therefore, there is now growing interest in air injection because of its availability. Air injection has been widely used in the past for production of viscous heavy oils, where the heat generated by in situ combustion is a necessary part of the recovery process. Air injection can also be used for the recovery of light oils, but in this case, heat generation is not necessary for the displacement. Some form of oxidation is only required in order to remove the oxygen from the air and prevent it from reaching the production wells. Yannimaras et al.(2) have discussed the benefits of air injection for IOR from deep, light oil reservoirs, wherein the principle objective was to generate flue gas (85﹪ N2, 15﹪ CO2) by in situ combustion. There are a number of ongoing successful air injection field projects, notably in the West Hackberry Field, Louisiana [Amoco(3)]; in Medicine Pole Hills Unit, North Dakota; Buffalo, South Dakota [Koch(4)]; most recently, in the Horse Creek Field, North Dakota [Total(5)]; and Total's proposed LTO pilot test in the H Field in Indonesia(6). In the latter case, core flooding studies were undertaken to investigate the effect of various parameters on oxygen uptake by the oil. Previous field projects and simulation studies have considered that high temperature oxidation (HTO, or in situ combustion) is needed to remove the oxygen and enhance oil recovery. Christopher(7) [see also Yannimaras et al.(8)] used an accelerating rate calorimeter (ARC) to screen light reservoir oils for continuous exothermicity. For light oils they found that about 20﹪ were good candidates for propagating full in situ combustion. This suggests that perhaps a majority of light oils will sustain only low temperature oxidation (LTO). Thus, when the primary objective is only to generate nitrogen and carbon dioxide in situ, then a less intensive oxidation process, without combustion, is sufficient. The focus is therefore on a spontaneous LTO process, which can be applied in all light oil reservoirs with sufficiently high reactivity to react with (and consume) oxygen in the injected air.

Recovery of light oil by air injection at medium temperature: Experiments

“…However, at shallower depths (300 ∼ 1000 m), an alternative is to inject at medium pressures (10 ∼ 90 bars) for light and medium oil in heterogenous low permeability reservoirs. High temperatures and high heat generation are not necessary for the displacement of light oil by air injection [22]. However some form of oxidation is required in order to remove the oxygen from the injected air [22] to prevent it from reaching the production wells, which is considered a safety hazard.…”

Experimental Study of the Feasibility of Air Flooding in an Ultra-Low Permeability Reservoir

“…A relatively high content of anions like HCO 3 − , while SO 4 2− ion content is relatively low. The details are listed in Table 2.…”

“…Many studies show that gas (including air, nitrogen, carbon dioxide, etc.) injection is an effective method to improve the development efficiency of low and extra-low permeability reservoirs [3][4][5][6][7], which can establish a valid driving force better than water injection. Less often considered is that most CO 2 used for enhanced oil recovery (EOR) is never recovered, but is actually stored in the reservoir permanently; this long-term sequestration helps offset the greenhouse gas (GHG) emissions from burning fossil fuels [8][9][10].…”

Oxidation wave structure and oxygen breakthrough for air injection into light oil reservoirs

“…There is high temperature oxidation (HTO) [30,31], in which cracking occurs forming coke, which is subsequently oxidized at high temperatures, and low temperature oxidation (LTO), in which the oxygen is absorbed or incorporated by the hydrocarbon molecules to form alcohols, aldehydes, acids, or other oxygenated hydrocarbons [16,17,19]. The LTO may be followed by complete scission of molecules into small reaction products such as water, CO, or CO 2 [14,17,18,22].…”