Dynamic characterization of microscopic pore structures of shale under the effect of hydration: A case study of Longmaxi Formation shale in the Changning area of the Sichuan Basin

被引：0

作者：

Zeng F. ^{[1
]}

Zhang Q. ^{[1
]}

Chen S. ^{[1
,2
]}

Guo J. ^{[1
]}

Fan Y. ^{[3
]}

Ren W. ^{[1
]}

Wang X. ^{[3
]}

机构：

[1] State Key Laboratory of Oil & Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu

[2] Downhole Service Company, CNPC Chuanqing Drilling Engineering Co., Ltd., Chengdu

[3] Research Institute of Shale Gas, PetroChina Southwest Oil & Gasfield Company, Chengdu

来源：

Natural Gas Industry | 2020年 / 40卷 / 10期

关键词：

Changning area; Clay mineral; Hydration; Hydration stress; Longmaxi Formation; Lower Silurian; Microscopic pore structure; Shale gas reservoir; Sichuan Basin; Soak time;

D O I：

10.3787/j.issn.1000-0976.2020.10.008

中图分类号：

学科分类号：

摘要：

In order to study the effects of hydration on shale pore structure in a real fracturing environment, this paper selected the samples of Lower Silurian Longmaxi Formation shale in the Changning area of the Sichuan Basin to carry out imbibition and hydration experiments of fracturing fluid under the reservoir temperature of 90℃. Then, the macroscopic evolution process of pore structure parameters (e.g. morphology, size and specific surface area) of shale sample particles after hydration of 0 d, 5 d, 10 d and 20 d were compared by means of scanning electron microscopy, low-temperature N2 adsorption, high-pressure mercury injection, CT scanning and other experiments. In addition, the reasons for the change of shale pore structure were analyzed. Finally, hydration experiments were carried out on single clay mineral (montmorillonite and illite) to compare the hydration characteristics of different clay minerals. And based on this, the influencing mechanism of hydration on shale microstructure was studied. And the following research results obtained. First, clay mineral hydration can promote the generation of micro-fractures between shale bedding planes. Hydration induced fractures are of small scale and dense distribution, so they can be locally interconnected in the microscopic level to improve the physical properties of shale reservoirs significantly. Second, as hydration goes on, micro-fractures approach to closure from propagation, and the pore volume increases first and then decreases. And it reaches the maximum value after hydration of 5 days. Third, the hysteresis of clay mineral hydration swelling relative to hydration stress change is the main reason for the change of shale microstructures, and the hydration swelling volume of illite is smaller than that of montmorillonite. Fourth, inorganic cations can inhibit clay mineral hydration, and the inhibition effects of K+, Na+ and Ca2+ become worse in turn. In conclusion, hydration can increase the permeability of shale reservoirs, and the reasonable soak time after the fracturing of Longmaxi Formation shale reservoirs in the study area is 5 days. As for the shale gas reservoirs with higher montmorillonite contents, however, it is recommended to extend the soak time appropriately. © 2020, Natural Gas Industry Journal Agency. All right reserved.

引用

页码：66 / 75

页数：9

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