Assessment of Fluid Residence Time in Reservoirs – Case Study of Radiolysis Effects in Crude Oils from China and Norway
Abstract
Fluid residence time in a trap is a key factor in many petroleum systems evaluation, basin modeling and carbon storage studies. It will not only provide constraints for basin modeling but also contribute an alternative approach to caprock efficiencies evaluations for carbon storage and oil charge studies. However, dating of fluid flow events in petroleum systems is currently based on indirect methods, and direct assessment of hydrocarbon charge and residence time from analysis of crude-oil is not feasible. In the 1990s, Frolov et al. examined abundant olefin concentrations in crude oil and proposed a new concept of olefin generation in crude oils by natural radiolytic dehydrogenation of saturated hydrocarbons. Motivated by this concept and development of radiation chemistry, the study of my thesis aims at investigating the radiolysis effects and mechanisms, identifying a hydrocarbon-related potential proxy system, and thus, to develop a new precise analytical method to permit functional dating of reservoirs by organic geochemical proxies with realistic reservoir gamma ray doses.
High-dose (0–10000 kGy) and low-dose (0–200 kGy) gamma ray irradiation experiments were designed and conducted on the selected crude oil samples from the Chinese Tarim Basin, the North Sea and the Barents Sea, which aim to find novel radiation damage products and discover potential radiolysis marker candidates as well as analytical methods to quantify them. The original and irradiated oil samples were separated into saturated and aromatic hydrocarbon fractions, and were characterized using gas chromatography-mass spectrometry (GC-MS). The high-dose irradiation results were applied to develop methods, study the key radiolysis mechanism and detect radiolysis markers, while low-dose irradiation results were further used to derive correction factors and build a more precise and realistic correlation between radiolysis proxies and irradiation dose.
After irradiation, the majority of GC-MS monitored compounds were destroyed at different rates. The rates are dependent on the original concentration, compound class, molecular size (carbon number) and the oil matrix. A few compounds, particularly n-alkanes C9–12, were generated after oil radiolysis. The dating proxies were determined from GC-MS results and preliminary dating concepts of the reservoir filling were developed. In an ideal scenario, knowing the irradiation dose and the reservoir radiation dose rate from analysis of samples would enable the calculation of reservoir residence age. Future work will further explore the analytical approaches, proxy modeling and the application of such concepts in case histories.
Description
Keywords
Geochemistry
Citation
Zhao, J. (2017). Assessment of Fluid Residence Time in Reservoirs – Case Study of Radiolysis Effects in Crude Oils from China and Norway (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/25028