Effect of CO2 Huff and Puff Rounds on Crude Oil Properties

The conversion coefficient C between relaxation time T 2 value and pore size was calibrated by a high-pressure mercury injection experiment, low-temperature nitrogen adsorption experiment, and NMR experiment for clarifying the effect of CO 2 huff and puff on the production characteristics of crude oil in shale micronano pores. Then, the effects of huff and puff rounds, the soaking time, and injection pressure on the seepage law of crude oil in shale pores from the microscopic scale were studied. The results showed that the pore size of the main occurrence space of shale oil was mainly distributed in the range of 1−100 nm. The oil production of matrix/matrix-fractured shale mainly depended on the first two rounds. Combined with MRI imaging technology, in the initial stage, CO 2 mainly used the crude oil in the surrounding area of the core for matrix shale, and CO 2 mainly used the crude oil in the fracture and the surrounding area of the fracture for matrix-fractured shale. With the increase of huff and puff rounds, the crude oil inside the core was gradually utilized through CO 2 diffusion for matrix shale and matrix-fractured shale. Prolonging the soaking time could significantly improve the recovery degree of crude oil in small pores, which increased by 4.21%, but the lower limit of pore size was reduced by only 2−3.4 nm. Increasing the injection pressure could not only reduce the lower limit of pore size, which was reduced by 2.4−3.9 nm, but also effectively improve the recovery degree of crude oil in different pores. Compared with the matrix shale core, the matrix-fractured shale core was more sensitive to the soaking time and injection pressure. The research results could provide some reference and guidance for the field test of CO 2 huff and puff in shale reservoirs.

Section: Introductionmentioning

confidence: 99%

Characteristics of Crude Oil Production in Microscopic Pores of CO₂ Huff and Puff in Shale Oil Reservoirs

Song,

Chang,

Guan

et al. 2024

“…Shi et al studied the effect of the CO 2 concentration on crude oil PVT properties through huff and puff experiments. The results showed that with the increase in CO 2 concentration, the viscosity and density of the produced oil decreased, the light components in the crude oil increased, the heavy components decreased, and the content of paraffin and resin asphaltene decreased . Liu et al proposed that CO 2 molecular diffusion plays a major role in extracting the crude oil in macropores by the online nuclear magnetic resonance method and has little effect on the crude oil in micropores …”

Section: Introductionmentioning

confidence: 99%

“…The results showed that with the increase in CO 2 concentration, the viscosity and density of the produced oil decreased, the light components in the crude oil increased, the heavy components decreased, and the content of paraffin and resin asphaltene decreased. 26 Liu et al proposed that CO 2 molecular diffusion plays a major role in extracting the crude oil in macropores by the online nuclear magnetic resonance method and has little effect on the crude oil in micropores. 27 During CO 2 huff and puff, injection parameters such as injection pressure, soaking time, injection timing, and huff and puff cycles are important factors affecting shale oil recovery.…”

Section: Introductionmentioning

confidence: 99%

Insights into Enhancing Shale Oil Recovery Postfracturing with CO₂ Huff and Puff and Elastic Depletion Development Strategies

Li,

Huang,

Duan

et al. 2024

After hydraulic fracturing, shale reservoirs often undergo rapid production declines during depleted development, resulting in a low cumulative production. CO 2 huff and puff emerges as a promising method to enhance shale oil recovery postfracturing. This study conducted independent experiments to investigate multistage depressurization elastic depletion development and the CO 2 huff and puff method in shale oil. The effects of injection pressure, temperature, fractures, and other parameters on the CO 2 huff and puff recovery were analyzed using nuclear magnetic resonance (NMR). The impact of the CO 2 huff and puff on crude oil in different pores was elucidated. The results show that the fluid mobility of the shale reservoir is poor, with the recovery rate of elastic depletion development being less than 10%. Conversely, a CO 2 huff and puff can enhance the recovery rate by up to 20%. The recovery rate of shale oil through a CO 2 huff and puff correlates positively with injection pressure and temperature. The initial cycle of huff and puff contributes the most to crude oil recovery, reaching up to 50%. Under equivalent parameter conditions, the presence of fractures can increase the CO 2 huff and puff efficiency by 20% compared to the matrix core. Combined with NMR experiments, the lower limit of pores that oil can be produce in matrix and fracture cores in elastic depletion development is 200 and 150 nm, respectively. In the context of CO 2 huff and puff development, these values decrease to 30 nm for matrix cores and 15 nm for fractured cores.

“…Considerable research has been conducted on CO 2 huff-n-puff in tight sandstone reservoirs. Previous studies have explored the effects of injection volume, injection pressure, and huff-n-puff cycles on recovery efficiency. − Ding et al considered the influence of four factors on CO 2 huff and puff times, matrix permeability, matrix size, and gas type and concluded that matrix permeability has a stronger influence on CO 2 huff and puff recovery than matrix size. Huang et al established a microreservoir classification standard based on field emission scanning electron microscopy (FE-SEM), CST, nanocomputed tomography (Nano-CT), HPMI, NMR, and other experimental methods, evaluating the influence of asphaltene content on pore structure and recovery efficiency.…”

Section: Introductionmentioning

confidence: 99%

Microscopic Production Characteristics of Huff-n-Puff after CO₂ Flooding in Tight Oil Sandstone Reservoirs

Xue,

Gao,

Wen

et al. 2023

This study aims to investigate the impact of CO2 huff-n-puff after CO2 flooding on recovery efficiency in tight sandstone reservoirs. The experimental methodology involved the selection of three representative cores with different permeability levels to emulate class I, II, and III reservoirs. To examine immiscible, nearly miscible, and miscible conditions for different reservoir samples, a physical simulation flow system integrated with nuclear magnetic resonance technology was employed. CO2 flooding was performed followed by CO2 huff-n-puff experiments at five pressures, enabling a quantitative analysis of oil production characteristics in various pores during the flooding and huff-n-puff processes. This study provides insights into the microscopic production characteristics and oil recovery influenced by huff-n-puff in tight sandstone reservoirs subsequent to CO2 flooding. The experimental results highlight that recovery efficiency increases with higher permeability, with class I reservoir samples exhibiting the highest recovery rate at 76.47%, followed by class II reservoirs at 69.33%, and class III reservoirs at 44.43%. Huff-n-puff recovery for class I and class II reservoirs gradually declines with increasing pressure after flooding, whereas class III reservoirs display an opposite trend, with recovery gradually increasing. In addition, the microscopic oil distribution characteristics change after flooding. During the near-miscible phase, class I and class III reservoirs predominantly yield oil from medium and small pores, while class II reservoirs primarily produce oil from medium pores. Upon reaching miscibility, oil production in class I, II, and III reservoirs primarily occurs in small pores, with some contribution from medium pores. The research findings presented in this paper provide valuable theoretical support for future CO2 flooding operations in tight sandstone reservoirs and the optimization of huff-n-puff experiments subsequent to flooding.