We study the effects of pressure on crude-oil oxidation kinetics using ramped temperature oxidation for a large range of pressures and heating rates (1.5, 2.0, 5.0, 7.5, 8.0, 10.0, 15.0, 20.0, and 30.0 °C/min). Results are relevant to the combustion of crude oil within reservoirs to produce heat and pressure that enhance oil recovery. Our study results suggest that the activation energy of global reactions is sensibly independent of changes in both partial pressure and total pressure (100−2000 psig) with values ranging between 50 and 60 kJ/mol for the low-temperature oxidation regime (roughly 250 °C) and 90−100 kJ/mol for the hightemperature oxidation regime (roughly 350−450 °C). Three different crude oils were tested. For one of the crude oils, we observe an increasing trend in oxygen consumption as the total pressure is increased up to a particular pressure (∼500 psig), after which it remains constant. This trend is, apparently, associated with the evaporation of relatively lighter components at low pressures, decreasing the amount of oil available for fuel generation. Total oxygen consumption starts to decrease again at very large pressures (>1500 psig), and we associate this trend with water phase behavior at these conditions.
Accelerating-Rate Calorimeter (ARC), Ramped-Temperature-Oxidation (RTO), and Combustion Tube (CT) tests are used for screening and designing air injection processes for enhanced oil recovery. These tests use different size samples of reservoir materials, operating under different conditions, have different interpretation requirements, and yield different types of information. ARC data have been used to provide rapid screening of the suitability of (especially) high pressure light oil reservoirs for air injection. Small reservoir samples are used, air injection displacement efficiency is not captured, but they provide explicit quantitative oxidation rate information. RTO experiments use larger quantities of core and reservoir fluids and allow some fluid displacement and production. Due to the nature of this type of test, a much larger fraction of the oil is consumed compared to field application, and oxidation data over a broad range of temperatures is implicitly provided. Finally, combustion tube tests provide the closest dynamic analog to actual reservoir conditions and have the largest core and fluid requirement. This paper describes a systematic procedure used to consolidate the data from these tests into a robust kinetic model for the design and implementation of air injection processes in heavy oil mature fields. The model considers both low and high temperature oxidation reactions, thermal cracking, and the compositional changes that the oil undergoes. Application of the model at the field scale shows temperature levels, produced gas compositions, and fuel and air requirements comparable with those derived from the combustion tube tests.
The geological, economic, and strategic conditions which make the discovery of large petroleum reservoirs a more risky and costly undertaking has resulted in having to consider mature fields and to conclude that the geology and the properties of fluids have an incidence in the final recovery of each reservoir, and that by understanding these factors it is possible to improve the recovery factor. The Lisama Field is located in the basin of the Middle Magdalena Valley, in Colombia, and is operated by ECOPETROL S.A. It is characterized by a complex of fluvial channels with thicknesses of between 10 and 20 ft, a restricted lateral continuity, lateral and vertical changes in the type of rock and depleted producing sands; this resulted in the need for new exploitation strategies which would allow the optimum recovery of the remaining reserves of the field. From a technical screening based on the properties of the rock, fluids, and the reservoir, the review of analogue fields worldwide and the experimental feasibility evaluated in the laboratory, the implementation of a water injection process resulted in a favorable method to be applied to the Lisama Field. Geological, petrophysical, fluids, and production information was integrated during the identification and selection of areas and stratigraphic intervals with the best characteristics for the implementation of the water injection process. Zone Quality Factor maps, isochors, average thickness and percentage of sand tied to stratigraphic correlations and reservoir rock-type thickness maps were analyzed to obtain the spatial distribution of the more powerful, continuous channels, with more effective pores systems, which, integrated with the production analysis, resulted in the delineation of the areas of interest. The prediction of the behavior of the water injection and the expected recovery of oil was obtained by means of an analytical and numerical simulation of the injection patterns as established.
In Situ Combustion (ISC) is a gas injection oil recovery process, the injection gas could be oxygen, air or enriched air. In the ISC process, heat is used as an adjuvant to improve the recovery. The heat is generated within the reservoir by burning a portion of the oil, the burning front is sustained by air injection (Sarathi 1999). The main displacement mechanisms are steam drive, miscible flue gas flooding and, viscosity reduction by oil swelling, temperature increase, among others. The ISC pherhaps is the most efficient enhanced oil recovery method and, possibly the best alternative to produce heavy oil reservoirs. However, despite the economic and technical success of field experiences, the oil industry has been reluctant to its implementation. Mainly, because is difficult to perform the scaling of the process from laboratory to field; any of the methodologies developed is completely reliable. An important point to understand the characteristics of oxidation/combustion of oil is the kinetic, this is usually obtained from Ramped Temperature Oxidation (RTO) tests and using the Arrhenius equation. However, in the last years have been introduced a new methodology named isoconversional principle. The technique provides direct information of effective activation energy and, it can be used as a screening tool to identify good candidates to ISC. In this paper are presented the results after applying the isoconversional principle in a Colombian heavy oil for the understanding of the oil oxidation/combustion characteristics.
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