Nuclear magnetic resonance experimental study of CO2 injection to enhance shale oil recovery

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.

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

SPE Journal ◽

10.2118/199345-pa ◽

2019 ◽

Vol 25 (01) ◽

pp. 440-450 ◽

Cited By ~ 4

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.

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Assessing the Efficiency of Saturating Shale Oil Cores and Evaluating Hydrocarbon Gas Huff ‘n’ Puff Using Nuclear Magnetic Resonance

SPE Reservoir Evaluation & Engineering ◽

10.2118/205027-pa ◽

2021 ◽

pp. 1-11

Author(s):

Sherifa E. Cudjoe ◽

Reza Barati ◽

Jyun-Syung Tsau ◽

Chi Zhang ◽

Brian Nicoud ◽

...

Keyword(s):

Nuclear Magnetic Resonance ◽

Magnetic Resonance ◽

Mineral Composition ◽

Oil Recovery ◽

Gas Diffusion ◽

Shale Oil ◽

Primary Yield ◽

The Impact ◽

Nuclear Magnetic ◽

Fluid Interactions

Summary Shale oil formations have a very low primary yield despite advances in multistage hydraulic fracturing and horizontal drilling. In so doing, gas huff ‘n’ puff (HnP), among other improved oil recovery methods, is implemented to recover more liquid hydrocarbons. Gas HnP has proven to be an effective recovery process in shales taking into account the fracture properties, fluid-fluid interactions, and gas diffusion controlled by matrix properties. However, a laboratory-scale understanding of the gas HnP mechanism proves challenging. At this scale, measuring saturation before and after HnP tests in a nonintrusive and nondestructive manner, and understanding rock properties that affect diffusion is essential. In addition to ascertaining how the multiscale pore systems and varying mineral composition of shales affect its evaluation. The nuclear magnetic resonance (NMR) is considered a suitable tool for estimating fluid content in shales and understanding rock/fluid interactions. Generally, synthetic oil samples are used on either outcrop core plugs or crushed reservoir samples for NMR measurements, which may not be representative of rock/fluid interactions in bulk shales. This study is focused on carrying out NMR tests with dead oil on reservoir core plugs at relatively different depths to determine an effective means of saturation and understand oil production due to gas HnP. Gas HnP experiments were performed at reservoir conditions (3,500 psi and 125°C) on representative rock types from the Lower Eagle Ford (LEF) interval. Low field NMR measurements were subsequently carried out on the LEF core plugs at different states: as-received, saturated, and after gas HnP. The results show that oil recovery due to gas HnP occurred mainly in the organic pores (OPs) and inorganic pores (IPs) and ranged from 48 to 56% of the oil-in-place with indications of adsorbed/trapped methane (CH4) and remaining heavier components. This plays a vital role in evaluating the HnP process to know the extent of invasion and remaining oil components. In saturating the core plugs, the optimum saturation period was found to be 2 weeks for the LEF shale at current conditions. This presents an idea of how long to saturate a shale oil core effectively before it is tested for gas HnP. On the basis of the impact of varying mineral composition on the recovery mechanism, we observed the LEF core plug with the highest clay content to have the least recovery. This is in line with a high T1/T2 ratio alluding to reduced mobility of fluids in the presence of clay minerals with relatively small sizes of clay porosity and adsorptive surfaces.

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Experimental study on drying characteristics of wheat by low-field nuclear magnetic resonance

Drying Technology ◽

10.1080/07373937.2016.1242492 ◽

2016 ◽

Vol 35 (10) ◽

pp. 1258-1265 ◽

Cited By ~ 15

Author(s):

Chao Jia ◽

Li Wang ◽

Ran Li ◽

Chuanping Liu

Keyword(s):

Experimental Study ◽

Nuclear Magnetic Resonance ◽

Magnetic Resonance ◽

Drying Characteristics ◽

Low Field ◽

Nuclear Magnetic

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

10.5194/egusphere-egu21-6762 ◽

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

The wettability, fingering effect and strong heterogeneity of carbonate reservoirs lead to low oil recovery. However, carbon dioxide (CO2) displacement is an effective method to improve oil recovery for carbonate reservoirs. Saturated CO2 nanofluids combines the advantages of CO2 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 CO2 flooding and saturated CO2 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 CO2 displacement experiment, the results show that viscous fingering and channeling are obvious during CO2 flooding, the oil is mainly produced from the big pores, and the residual oil is trapped in the small pores. For the saturated CO2 nanofluids displacement experiment, the results show that saturated CO2 nanofluids inhibit CO2 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 CO2 nanofluids displacement is higher than that of CO2 displacement. This study provides a significant reference for EOR in carbonate reservoirs. Meanwhile, it promotes the application of nanofluids in energy exploitation and CO2 utilization.

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