Pore changes of slickwater-containing shale under supercritical CO2 treatment

Lu, Yiyu; Liu, Jie; Tang, Jiren; Ao, Xiang; Li, Honglian; Zhou, Jiankun; Sun, Xiao Fei

doi:10.1016/j.fuel.2021.122775

Cited by 24 publications

(18 citation statements)

References 69 publications

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“…These changes illustrated that the interactions between fracturing fluid and PR shale caused a more serious increase in pore volume especially the meso- and macropores, which was consistent with the analysis of pore-structure parameters. According to the previous research report, the pore area was mainly determined by small pores, while the pore volume was mainly by large pores; 31 thus, the pore area increased with the growing number of mesopores, and the pore volume increased with the growing number of meso- and macropores for the reacted PR shale.…”

Section: Resultsmentioning

confidence: 79%

“…Previous studies demonstrated that D 2 was positively related to the total specific surface and pore volume, while negatively related to average pore diameter. 31,50 As discussed above, the TSSA and TPV of the PR shale increased and R a decreased after slickwater treatment, which was induced by the increase in mesopores. Thus, the growth in the number of mesopores in the PR shale led to an increase in the pore-structure complexity and a weakening in the pore connectivity.…”

Section: Evolution Of Pore Area and Volume Distributionmentioning

confidence: 75%

“…A previous study demonstrated that when the formation of new small pores was larger than the transformation degree of small pores to large pores, the R a would show a decreasing trend. 31 To deeply explore the changed characteristics of micro-, meso-, and macropores before and after reaction with fracturing fluid, the percentage of each type of pore was calculated ( Figure 5 ). The unreacted PR and PP shale mainly contained meso- and macropores, which provided more than 90% of the TPV.…”

Section: Resultsmentioning

confidence: 99%

“…The decreasing rates of TSSA and TPV were 33.2 and 22.9%, respectively, and the R a increased from 5.976 to 6.893 nm. A previous study demonstrated that when the formation of new small pores was larger than the transformation degree of small pores to large pores, the R a would show a decreasing trend . To deeply explore the changed characteristics of micro-, meso-, and macropores before and after reaction with fracturing fluid, the percentage of each type of pore was calculated (Figure ).…”

Section: Resultsmentioning

confidence: 99%

“…During the experiment, 10 mL of each solution was collected (24, 48, and 72 h), and the pH of the solution was monitored. After the reaction, the shale samples were cleaned using deionized water and heated to dry at 50 °C for 12 h in an oven to minimize the influence of free water and weakly bounded water in shale pores . Then, they were collected for analyzing the mineralogy and pore-structure characteristics.…”

Section: Methodsmentioning

confidence: 99%

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Impact of Pyrite Oxidation on the Pore-Structure Characteristics of Shale Reservoir Rocks under the Interaction of Fracturing Fluid

Sun

et al. 2022

ACS Omega

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Hydraulic fracturing combined with horizontal drilling is widely used to develop shale gas resources, and huge amounts of fracturing fluid are injected into shale reservoirs. However, the fracturing fluid is ineluctably retained in reservoir rocks after fracturing, resulting in the alteration of shale pore systems and further affecting the hydrocarbons production efficiency. In this work, two types of shales with different pyrite contents, namely, pyrite rich (PR, Niutitang Formation) and pyrite poor (PP, Xiamaling Formation), were emphasized to illustrate the effect of pyrite oxidation on pore structure after fracturing operation. Slickwater fracturing fluid was used to treat the shale samples for a period of 3 days, under the condition of 100 °C and 50 MPa. The field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were utilized to determine the surface morphology and mineral composition. The low-temperature N 2 adsorption was performed to quantify the pore structure. The results showed that the pyrite oxidation induced the dissolution of both the pyrite and calcite and generated many dissolution pores for the pyrite-rich shale after slickwater treatment. The mineral dissolution led to an increase in the number of mesopores, enlarged the total specific surface area (TSSA) and total pore volume (TPV), and strengthened the pore-structure complexity. On the other hand, the pyrite-poor shale only experienced clay swelling after slickwater treatment. Its pore surface roughness and pore-structure complexity degraded with the loss of nanopores and the reductions in TSSA and TPV. The results of this study enhance the understanding of the impact of pyrite oxidation on the pore structure and provide new insight into the optimization of fracturing operation conditions based on shale’s mineral composition characteristics.

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Section: Resultsmentioning

confidence: 79%

Section: Evolution Of Pore Area and Volume Distributionmentioning

confidence: 75%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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