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Case Studies and Field Applications
Published in Francisco M. Vargas, Mohammad Tavakkoli, Asphaltene Deposition, 2018
M. I. L. Abutaqiya, C. Sisco, J. Kuang, P. Lin, F. Wang, M. Tavakkoli, F. M. Vargas
Hydrocarbon gas injection is usually performed to maintain reservoir pressure and, thus, maintain production. This gas typically originates as an associated gas which is coproduced with oil or it may be produced separately from surrounding gas wells. Before undertaking gas injection for enhanced oil recovery (EOR), oil producers first perform flow assurance studies on the live oil sample to understand the potential occurrence and severity of asphaltene precipitation and deposition problems as a function of gas amount and composition. These high-pressure, high-temperature (HPHT) experiments, however, are expensive, time-consuming, and may be subject to significant and, sometimes unknown, experimental uncertainties (Section 3.2). A modeling method based on PC-SAFT EOS can be used to design and analyze such experiments, and hence, reduce the need of extensive experimental work and increasing the consistency of the results. Figure 8.2 summarizes a case in which PC-SAFT was used to simulate the effect of gas injection on asphaltene precipitation. The simulation parameters were tuned to the live oil experiments for Crude U8 (off-shore field). Crude U8 is the fluid that was characterized in Section 4.4.1 and its properties and simulation parameters can be found therein. The results for the gas injection at 10 mol%, 20 mol%, and 30 mol% cases are purely predictive, and the gas composition is provided in the figure caption. The excellent agreement between the PC-SAFT predictions and the HPHT experiments confirms the reliability of this EOS for designing the experiments and validating the consistency of the results.
The physical simulation experiment of lean gas injection in high-pressure and low-permeability reservoirs
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Maolei Cui, Rui Wang, Chengyuan Lv, Zengmin Lun, Yongqiang Tang, Pufu xiao
The original formation pressure is high in the deep-buried high-pressure and low-permeability reservoir. In the early stage of development, high production gas oil ratio, rapid drawdown of formation pressure and oil production have occurred as a result of poor water injection. At present, there are many problems in the development of deep-buried high-pressure and low-permeability reservoirs at home and abroad, such as difficulty of water injection, poor effect of water drive and low water-flooding degree (Nie 2017; Sun 2016). There are several advantages of gas reinjection, such as good injectivity and displacement efficiency. Gas reinjection can not only realize energy saving and emission reduction, but also supply formation energy, enhance oil recovery and increase economic benefits, especially for reservoirs with high gas oil ratio. In China, many oilfields, such as Tuha, Zhongyuan, and Changqing, have carried out field tests of natural gas injection, and achieved certain effect (Huang 2005; Li 2006; Wan 2013; Yuan, Zhao, and Zhang et al. 2002; Zhang, Cheng, and Liu 2019; Zhang, Mei, and Li et al. 2003; Zhang et al, 2015; Zhu 2018). In abroad, many researches on lean-gas reinjection in unconventional reservoirs have been studied (Akinluyi et al, 2018; Carpenter 2018). The former researches on natural gas flooding mainly focus on macrocosmic mechanism, theoretical calculation and the injection effect in the field test, but the microscopic mechanism is not clear yet. In this article, based on the field test of natural gas reinjection after depletion in the oil field in the east of China, the microscopic experiments have been conducted on the porous media model of glass etching in the high-temperature and high pressure (HTHP) micro-visualization experimental device. The microscopic interaction process between injected gas and formation fluid before and after depletion is studied, and the flow law of injected gas after depletion and the influence of water on gas drive process are clarified, which can reveal the microscopic oil displacement mechanism of lean gas injection in high-pressure and low-permeability reservoir.