Identification of distinctions of immiscible CO2 huff and puff performance in Chang-7 tight sandstone oil reservoir by applying NMR, microscope and reservoir simulation

Luo, Yongcheng; Zheng, Taiyi; Hu, Xiao; Liu, Xiangui; Zhang, Haiqin; Wu, Zhenkai; Zhao, Xinli; Xia, Debin

doi:10.1016/j.petrol.2021.109719

Cited by 16 publications

(9 citation statements)

References 24 publications

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“…39 The correlation analysis results are in good accordance with those of previous studies. 34,39 3.3. Air Flooding Mechanism of Shale Oil Reservoir.…”

Section: Microscopic Pore Crude Oil Production Characteristics Of Shalesupporting

confidence: 90%

“…The online NMR spectrometer is applied to record the NMR T 2 data of saturated crude oil samples, and the hydrogen signal value is a direct reflection of crude oil. 39 The formula for calculating the initial oil saturation P oci is…”

Section: Resultsmentioning

confidence: 99%

“…The online NMR spectrometer is applied to record the NMR T 2 data of saturated crude oil samples, and the hydrogen signal value is a direct reflection of crude oil . The formula for calculating the initial oil saturation P oci is P oci = ∑ T 2 , min T 2 , max A i , j − ∑ T 2 , min T 2 , max A i , normalb ∑ T 2 , min T 2 , max A i , normalo − ∑ T 2 , min T 2 , max A i , normalb × 100 % where P oci is the oil content (%); T 2,min and T 2,max are the minimum and maximum T 2 relaxation times, respectively (ms); and A i , j , A i ,o , and A i ,b are the corresponding signal strength values of NMR T 2 relaxation time curves of saturated oil, the signal strength of oil-bearing NMR after different core experiments, and the NMR spectrometer base semaphore, respectively (A m –1 ).…”

Section: Resultsmentioning

confidence: 99%

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Microscopic Production Characteristics of Pore Crude Oil and Influencing Factors during Enhanced Oil Recovery by Air Injection in Shale Oil Reservoirs

Yang

Feng

et al. 2023

ACS Omega

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High-pressure air injection (HPAI) is one of the effective methods to improve shale oil recovery after the primary depletion process. However, the seepage mechanisms and microscopic production characteristics between air and crude oil are complicated in porous media during the air flooding process. In this paper, an online nuclear magnetic resonance (NMR) dynamic physical simulation method for enhanced oil recovery (EOR) by air injection in shale oil was established by combining high-temperature and high-pressure physical simulation systems with NMR. The microscopic production characteristics of air flooding were investigated by quantifying fluid saturation, recovery, and residual oil distribution in different sizes of pores, and the air displacement mechanism of shale oil was discussed. On this basis, the effects of air oxygen concentration, permeability, injection pressure, and fracture on recovery were studied, and the migration mode of crude oil in fractures was explored. The results show that the shale oil is mainly found in <0.1 μm (small pores), followed by 0.1–1 μm (medium pores), and 1–10 μm (macropores); thus, it is critical to enhancing oil recovery in pores less than 0.1 and 0.1–1 μm. The low-temperature oxidation (LTO) reaction can occur by injecting air into depleted shale reservoirs, which has a certain effect on oil expansion, viscosity reduction, and thermal mixing phases, thereby greatly improving shale oil recovery. There is a positive relationship between air oxygen concentration and oil recovery; the recoveries of small pores and macropores can increase by 3.53 and 4.28%, respectively, and they contribute 45.87–53.68% of the produced oil. High permeability means good pore-throat connectivity and greater oil recovery, and the production degree of crude oil in three types of pores can be increased by 10.36–24.69%. Appropriate injection pressure is beneficial to increasing the oil–gas contact time and delaying gas breakthrough, but high injection pressure will result in early gas channeling, which causes the crude oil in small pores to be difficult to produce. Notably, the matrix can supply oil to fractures due to the mass exchange between matrix fractures and the increase of the oil drainage area, and the recoveries of medium pores and macropores in fractured cores increased by 9.01 and 18.39%, respectively; fractures can act as bridges for matrix crude oil migration, which means that proper fracturing before gas injection can make the EOR better. This study provides a new idea and a theoretical basis for improving shale oil recovery and clarifies the microscopic production characteristics of shale reservoirs.

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“…39 The correlation analysis results are in good accordance with those of previous studies. 34,39 3.3. Air Flooding Mechanism of Shale Oil Reservoir.…”

Section: Microscopic Pore Crude Oil Production Characteristics Of Shalesupporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Microscopic Production Characteristics of Pore Crude Oil and Influencing Factors during Enhanced Oil Recovery by Air Injection in Shale Oil Reservoirs

Yang

Feng

et al. 2023

ACS Omega

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“…Most of the reported studies of cyclic injection enhanced oil recovery (EOR) were implemented extensively using CO 2 in shale and tight reservoirs − and others used lean gas, methane, rich gas, or gas mixture. − Very little research was conducted using cyclic N 2 injection. − Yu and Sheng conducted an experimental study using N 2 and Eagle Ford shale cores. They soaked the cores in mineral oil before conducting the experiments.…”

Section: Introductionmentioning

confidence: 99%

Asphaltene Precipitation and Deposition during Nitrogen Gas Cyclic Miscible and Immiscible Injection in Eagle Ford Shale and Its Impact on Oil Recovery

Elturki

Imqam

2022

Energy Fuels

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Cyclic gas injection methods have been shown to improve oil recovery in conventional reservoirs. Even though similar technologies have been used in unconventional reservoirs with some success stories in shale resources, cyclic gas injection enhanced oil recovery (EOR) is still a little-understood subject in boosting oil recovery from unconventional reservoirs. During gas injection, asphaltenes start to deposit and precipitate, which causes pore plugging and reduces oil recovery. Studies of asphaltene deposition challenges during cyclic nitrogen (N 2 ) gas injection and oil production in unconventional reservoirs are yet relatively limited. Therefore, a comprehensive experimental study was conducted using 12 Eagle Ford shale cores (dynamic mode), and filter paper membranes (static mode) were used to evaluate whether miscible and immiscible huff-n-puff (cyclic) N 2 injection increases oil recovery and aggravates asphaltene precipitation. To ensure that miscibility can be examined in cyclic experiments, N 2 minimum miscibility pressure (MMP) was determined using a slim tube technique. The factors studied included the injection pressure, number of cycles, production time, and injection cyclic mode, all conducted at 70 °C. The findings showed that a high asphaltene weight percent was calculated during static experiments (i.e., using filter membranes), and this increase was severe on smaller pore size structures. Dynamic tests (i.e., using shale cores) showed that miscibility increased oil recovery, but a stronger intermediate-wet system was observed when measuring the wettability of cores after N 2 cyclic tests. When starting with shorter soaking times, more oil recovery could be achieved. Oil recovery reduction and asphaltene depositions were observed at later cycles. Microscopy and scanning electron microscopy (SEM) imaging of the Eagle Ford cores showed asphaltene clusters inside the cores after cyclic tests. A mercury porosimeter emphasized the degree of pore plugging after cyclic tests, and the findings revealed a smaller pore size distribution after N 2 tests due to the asphaltene deposition process when compared to cores that had not been pressured. This extensive study focuses on the effects of asphaltene deposition on oil recovery under cyclic N 2 -miscible and immiscible conditions in shale resources.

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“…Recently, gas huff-n-puff and flooding processes have been studied extensively in shale resources by various approaches, including experimental studies, − field pilots, , and simulation work. − Using N 2 and Eagle Ford shale cores, Yu and Sheng carried out an experimental investigation. They used mineral oil to saturate the cores and to perform the study.…”

Section: Introductionmentioning

confidence: 99%

Experimental Investigation of Asphaltene Deposition and Its Impact on Oil Recovery in Eagle Ford Shale during Miscible and Immiscible CO₂ Huff-n-Puff Gas Injection

Elturki

Imqam

2023

Energy Fuels

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One of the challenges in extracting oil from unconventional resources using hydraulic fracturing and horizontal drilling techniques is the low primary recovery rate, which is caused by the ultra-small permeability of these resources. Consequently, it is essential to investigate gas injection methods to produce the trapped oil in shale formations. However, the injection process can cause asphaltene depositions inside the reservoir, leading to plugging of pores and oil recovery (OR) reduction. There has been limited research on using gas injection techniques to improve oil production in tight/unconventional resources, although carbon dioxide (CO2) and gas-enhanced oil recovery methods have been used in conventional resources. In order to determine whether or not the cyclic (huff-n-puff) CO2 process improves OR and aggravates asphaltene precipitation, a rigorous experimental investigation was undertaken utilizing filter membranes and Eagle Ford shale cores. After the minimum miscibility pressure was calculated for CO2, various injection pressures were selected to perform CO2 huff-n-puff experiments. Investigations were carried out at 70 °C on injection pressure, cycle number, production time, and huff-and-puff mode injection. The results demonstrated that when the pore size structure of the membranes used was smaller and gas injection cycles increased, a higher asphaltene weight percent (wt %) was determined during the static experiments (i.e., employing filter paper membranes). Miscibility improved OR in dynamic testing (i.e., using shale cores), but a more oil-wet system was detected in wettability measurements taken following CO2 huff-and-puff tests. The plugging impact of asphaltene particles on the pore structure was studied using optical microscopy and scanning electron microscopy imaging. Following the huff-and-puff tests, a mercury porosimeter revealed how severely the pores were plugged, and after the CO2 tests, the pore size distribution reduced as a consequence of asphaltene deposition. This study examines the significance of CO2 injection in OR under miscible/immiscible conditions to identify the critical parameters that could impact the effectiveness of CO2 huff-n-puff operation in unconventional formations.

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Identification of distinctions of immiscible CO2 huff and puff performance in Chang-7 tight sandstone oil reservoir by applying NMR, microscope and reservoir simulation

Cited by 16 publications

References 24 publications

Microscopic Production Characteristics of Pore Crude Oil and Influencing Factors during Enhanced Oil Recovery by Air Injection in Shale Oil Reservoirs

Microscopic Production Characteristics of Pore Crude Oil and Influencing Factors during Enhanced Oil Recovery by Air Injection in Shale Oil Reservoirs

Asphaltene Precipitation and Deposition during Nitrogen Gas Cyclic Miscible and Immiscible Injection in Eagle Ford Shale and Its Impact on Oil Recovery

Experimental Investigation of Asphaltene Deposition and Its Impact on Oil Recovery in Eagle Ford Shale during Miscible and Immiscible CO₂ Huff-n-Puff Gas Injection

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Identification of distinctions of immiscible CO2 huff and puff performance in Chang-7 tight sandstone oil reservoir by applying NMR, microscope and reservoir simulation

Cited by 16 publications

References 24 publications

Microscopic Production Characteristics of Pore Crude Oil and Influencing Factors during Enhanced Oil Recovery by Air Injection in Shale Oil Reservoirs

Microscopic Production Characteristics of Pore Crude Oil and Influencing Factors during Enhanced Oil Recovery by Air Injection in Shale Oil Reservoirs

Asphaltene Precipitation and Deposition during Nitrogen Gas Cyclic Miscible and Immiscible Injection in Eagle Ford Shale and Its Impact on Oil Recovery

Experimental Investigation of Asphaltene Deposition and Its Impact on Oil Recovery in Eagle Ford Shale during Miscible and Immiscible CO2 Huff-n-Puff Gas Injection

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Experimental Investigation of Asphaltene Deposition and Its Impact on Oil Recovery in Eagle Ford Shale during Miscible and Immiscible CO₂ Huff-n-Puff Gas Injection