Monitoring CO2 Saturation Using Three-Detector PNC Logging Technique for CO2 EOR in Heavy Oil Reservoir
- Feng Zhang (School of Geosciences, China University of Petroleum / Key Laboratory of Deep Oil and Gas) | Quanying Zhang (School of Geosciences, China University of Petroleum) | Lili Tian (School of Geosciences, China University of Petroleum) | Xiaoyang Zhang (School of Materials Science and Engineering, Qingdao University of Science and Technology) | Qian Chen (School of Geosciences, China University of Petroleum) | Jilin Fan (School of Geosciences, China University of Petroleum)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- SPWLA 60th Annual Logging Symposium, 15-19 June, The Woodlands, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2019. held jointly by the Society of Petrophysicists and Well Log Analysts (SPWLA) and the submitting authors
- 1 in the last 30 days
- 89 since 2007
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CO2 enhanced oil recovery (CO2-EOR) project is of significance for CO2 sequestration and heavy oil recovery. Quantitative monitoring of CO2 saturation (SCO2) is essential to recognizing and understanding the migration and distribution of CO2 injected into the geological formations. Comparing with pore water and heavy oil, CO2 has zero hydrogen index and lower density under formation temperature and pressure. When the CO2 flood is injected into a heavy oil reservoir, the neutron moderation ability of the reservoir will dramatically change due to CO2 gas replacing parts of the heavy oil, and such different physical characteristics can be indicated using different spacing detector. In this paper, based on the difference in the neutron moderation ability of CO2, water and heavy oil, a three-detector pulsed neutron capture (PNC) logging technique is applied in heavy oil reservoirs to monitor CO2 sequestration. We propose a new parameter D, the difference of R13 and R23, where R13 represents the capture gamma count ratio of near to long detectors, and R23 is the count ratio of far to long detectors. The difference D can be used to determine CO2 gas saturation and the higher value of D results in more accurate estimation of gas saturation. In addition, it has higher sensitivity than count ratio R13 and R23.
By Monte Carlo simulation, the responses of gamma ray count ratio under different porosities and CO2 saturation were studied. Then, a mathematical model of CO2 saturation versus D and formation porosity was established to quantitatively calculate CO2 saturation. Besides, the effects of formation pressure and temperature, heavy oil density, lithology, and other factors on this method were studied. Results show that variations of formation pressure, formation temperature, and density of heavy oil have little impact on the CO2 saturation measurement. However, the change of formation lithology results in larger CO2 saturation errors and needs corrections. In addition, the method has a weak discrimination between CO2 and CH4 gas, so the results are easily affected by the CH4 content. Finally, a simulated case demonstrates the application of the method. For the heavy-oil sandstone with different porosities, the method shows a perfect performance: the SCO2 errors are less than 1% for the high and low gas saturated formation. This research provides an effective strategy to monitor CO2 storage and residual oil saturation in CO2-EOR reservoirs.
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