scholarly journals Effect of permeability and fractures on oil mobilization of unconventional resources during CO2 EOR using nuclear magnetic resonance

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Huanquan Sun ◽  
Haitao Wang ◽  
Zengmin Lun
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Exposure Time ◽  
Oil Recovery ◽  
Ordos Basin ◽  
Tight Oil ◽  
Unconventional Resources ◽  
Exposure Experiment ◽  
Core Permeability ◽  
Nuclear Magnetic

AbstractCO2 EOR (enhanced oil recovery) will be one of main technologies of enhanced unconventional resources recovery. Understanding effect of permeability and fractures on the oil mobilization of unconventional resources, i.e. tight oil, is crucial during CO2 EOR process. Exposure experiments based on nuclear magnetic resonance (NMR) were used to study the interaction between CO2 and tight oil reservoirs in Chang 8 layer of Ordos Basin at 40 °C and 12 MPa. Effect of permeability and fractures on oil mobilization of exposure experiments were investigated for the different exposure time. The oil was mobilized from matrix to the surface of matrix and the oil recovery increased as the exposure time increased. The final oil recovery increased as the core permeability increased in these exposure experiments. Exposure area increased to 1.75 times by fractures resulting in that oil was mobilized faster in the initial stage of exposure experiment and the final oil recovery increased to 1.19 times from 28.8 to 34.2%. This study shows the quantitative results of effect of permeability and fractures on oil mobilization of unconventional resources during CO2 EOR, which will support CO2 EOR design in Chang 8 layer of Ordos Basin.

Nuclear-Magnetic-Resonance Study on Oil Mobilization in Shale Exposed to CO2

SPE Journal ◽  
2019 ◽  
Vol 25 (01) ◽  
pp. 432-439
Author(s):  
Haitao Wang ◽  
Zengmin Lun ◽  
Chengyuan Lv ◽  
Dongjiang Lang ◽  
Ming Luo ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Exposure Time ◽  
Oil Recovery ◽  
Oil Content ◽  
Salt Content ◽  
Co2 Injection ◽  
Oil Reservoir ◽  
Shale Oil ◽  
Nuclear Magnetic

Summary Reservoirs in the Qian 34 10 rhythmic layer of the Qianjiang Basin are shale oil reservoirs with intersalt sediments. During the natural depletion and development process, production rate of oil decreases rapidly. Water injection and CO2 injection are potential technologies for enhanced oil recovery (EOR) in shale. Because of high salt content in formations, unsaturated water dissolves salt and damages reservoirs. CO2 does not react with salt, and CO2 injection does not damage reservoirs. Moreover, CO2 could enter the micropores of the reservoir rocks and mobilize oil by diffusion, extraction, and swelling mechanisms. To verify oil mobilization in the shale exposed to CO2, exposure experiments based on nuclear magnetic resonance (NMR) were conducted in this study. NMR T2 spectrum could reflect the oil in place and be used to calculate the oil content of rock with low permeability. In this study, 10 fresh shale samples (from six depths) were analyzed, and the oil contents were determined using NMR T2 spectra. Two of the shale samples with high oil contents were selected for the CO2-exposure experiment. At a temperature of 40°C and a pressure of 17.5 MPa, the fresh shale samples were exposed to CO2, and the NMR T2 spectra obtained were used to continuously determine the oil content of the shale. The oil mobilization in the shale exposed to CO2 was determined. The results of the NMR T2 spectra showed that the NMR volume fractions of the remaining oil in seven fresh shale samples were above 10%. The recovery of the S5# shale exposed to CO2 was 51.2% after 8 days, whereas that of the S9# shale was 55.8% after 6.1 days. These results indicated that more than half of the shale oil was mobilized during the relatively long exposure time after CO2 injection. NMR T2 spectroscopy results also showed that oil in all pores could be mobilized as the exposure time increased. This study showed the quantitative results of the CO2-injection method and EOR in a shale oil reservoir of the Qianjiang Basin. All conclusions support starting a CO2-EOR pilot project in the shale oil reservoir with intersalt sediments with ultralow permeability.

Saturated carbon dioxide nanofluids enhanced oil recovery in carbonate reservoir cores using nuclear magnetic resonance

2021 ◽  
Author(s):  
Yongsheng Tan ◽  
Qi Li ◽  
Liang Xu ◽  
Xiaoyan Zhang ◽  
Tao Yu
Keyword(s):  
Carbon Dioxide ◽  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Enhanced Oil Recovery ◽  
Oil Recovery ◽  
Carbonate Reservoir ◽  
Carbonate Reservoirs ◽  
Residual Oil ◽  
Core Flooding ◽  
Nuclear Magnetic

<p>The wettability, fingering effect and strong heterogeneity of carbonate reservoirs lead to low oil recovery. However, carbon dioxide (CO<sub>2</sub>) displacement is an effective method to improve oil recovery for carbonate reservoirs. Saturated CO<sub>2</sub> nanofluids combines the advantages of CO<sub>2</sub> and nanofluids, which can change the reservoir wettability and improve the sweep area to achieve the purpose of enhanced oil recovery (EOR), so it is a promising technique in petroleum industry. In this study, comparative experiments of CO<sub>2</sub> flooding and saturated CO<sub>2</sub> nanofluids flooding were carried out in carbonate reservoir cores. The nuclear magnetic resonance (NMR) instrument was used to clarify oil distribution during core flooding processes. For the CO<sub>2</sub> displacement experiment, the results show that viscous fingering and channeling are obvious during CO<sub>2</sub> flooding, the oil is mainly produced from the big pores, and the residual oil is trapped in the small pores. For the saturated CO<sub>2</sub> nanofluids displacement experiment, the results show that saturated CO<sub>2</sub> nanofluids inhibit CO<sub>2</sub> channeling and fingering, the oil is produced from the big pores and small pores, the residual oil is still trapped in the small pores, but the NMR signal intensity of the residual oil is significantly reduced. The final oil recovery of saturated CO<sub>2</sub> nanofluids displacement is higher than that of CO<sub>2</sub> displacement. This study provides a significant reference for EOR in carbonate reservoirs. Meanwhile, it promotes the application of nanofluids in energy exploitation and CO<sub>2</sub> utilization.</p>

Nuclear-Magnetic-Resonance Monitoring of Mass Exchange in a Low-Permeability Matrix/Fracture Model During CO2 Cyclic Injection: A Mechanistic Study

SPE Journal ◽  
2019 ◽  
Vol 25 (01) ◽  
pp. 440-450 ◽  
Author(s):  
Bing Wei ◽  
Ke Gao ◽  
Tao Song ◽  
Xiang Zhang ◽  
Wanfen Pu ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Oil Recovery ◽  
Mass Exchange ◽  
Fracture Model ◽  
Co2 Injection ◽  
The Matrix ◽  
Tight Reservoirs ◽  
Cyclic Injection ◽  
Nuclear Magnetic

Summary Recent reports have demonstrated that carbon dioxide (CO2) injection can further raise the oil recovery of fractured tight reservoirs after natural depletion, with major projects in progress worldwide. There is, however, a lack of understanding of the mass-exchange process between the matrix and fracture at pore scale. In this study, a matrix (0.8 md)/fracture model was designed to experimentally simulate a CO2-cyclic-injection process at 80°C and 35 MPa (Lucaogou tight formation). The oil (dead-oil) concentration in the matrix and fracture was continuously monitored online using a low-field nuclear-magnetic-resonance (NMR) technique aiming to quantify the oil recovery in situ and clarify the mass-exchange behaviors. The results showed that CO2 cyclic injection was promising in improving the oil recovery of fractured tight reservoirs. Nevertheless, the oil-recovery rates rapidly declined with the cycle of CO2 injection and the incremental oil was primarily produced by large pores with 100 ms > T2 > 3.0 ms. The NMR T2 profiles of the model evidenced the drainage of the matrix oil by CO2 toward the fracture. Because of the light-hydrocarbon extraction, the produced oils became lighter than the original oil. We noted that the main driving forces of the incremental oil recovery were CO2 displacement, CO2/oil interactions (mainly extraction and solubility), and pressure gradient (depressurization). In the first cycle, the CO2/oil interactions driven by CO2 diffusion during soaking enhanced the mass exchange between the matrix and the fracture. However, from the second cycle, CO2/oil interactions and CO2 displacement became insignificant. The results of this study supplement earlier findings and can provide insights into the CO2-enhanced-oil- recovery (EOR) mechanisms in fractured tight reservoirs. NOTE: Supporting information available.

Characteristics of the Micro-Nanopore System in a Pelitic Dolomite Reservoir: A Case Study of the Lower Cretaceous Xiagou Formation in the Qingxi Depression Based on Nuclear Magnetic Resonance Experiments

2021 ◽  
Vol 21 (1) ◽  
pp. 438-449
Author(s):  
Weifeng Sun ◽  
Wei Ju ◽  
Yan Song ◽  
Yong Qin
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Lower Cretaceous ◽  
Pore Radius ◽  
Bimodal Distribution ◽  
High Peak ◽  
Tight Oil ◽  
Distribution Shape ◽  
Group I ◽  
Nuclear Magnetic

The Lower Cretaceous Xiagou Formation is an important tight oil reservoir in the Qingxi Depression of the Jiuxi Basin. The micro-nanopore system within the reservoir requires a comprehensive analysis to improve the production of tight oil there. Nuclear magnetic resonance (NMR) experiments have been widely used for the petrophysical characterization of sandstones and carbonates. In the present study, the NMR experiment was applied to obtain the characteristics of the micro-nanopore system and permeability in the Lower Cretaceous Xiagou pelitic dolomite reservoir. According to the distribution shape of the transversal relaxation time (T2) obtained under the 100% water-saturated condition (Sw), the samples are divided into four groups: (i) group I, two obvious peaks (P1 and P2); (ii) group II, an obvious high peak of P1 at 0.1˜1.0 ms and a relatively low peak of P2; (iii) group III, an obvious high peak of P2 and a relatively low peak of P1; and (iv) group IV, three peaks. In general, the distribution shape of T2 under the initial condition (Sini) is unimodal, with all its peaks lower than those under the Sw condition. The NMR T2 spectrum reflects the distribution of the rock pore radius. Most of the pore radius distributions are bimodal, and the main pore radius ranges from 10 nm to 70 nm. Three patterns can be identified and determined based on the distribution of the pore radius: I—unimodal distribution, II—bimodal distribution and III—trimodal distribution. The results indicate that the porosity in the Xiagou reservoir ranges from 1.17% to 6.89%, with an average of 3.33%. The permeability ranges from 0.03×10−3 μm2 to 22.56×10−3 μm2, with an average of 2.95×10−3 μm2.

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