水相渗吸对页岩储层的物化作用机理研究

doi:10.13809/j.cnki.cn32-1825/te.2023.01.007

摘要/Abstract

摘要：

页岩气藏储层发育微纳米孔喉和裂缝，黏土矿物含量高，岩石渗透率低且非均质性较强，通常需要经过大规模水力压裂才能被有效开采。水力压裂过程中水相的自发渗吸将对页岩气藏储层产生一系列物化作用，改变页岩气藏储层的孔隙结构及物化性质，从而影响页岩气的产出。为进一步明确水相渗吸对页岩气藏储层的影响机理，开展了页岩重复渗吸对照实验，并基于页岩渗吸前后矿物溶蚀导致的质量变化、扫描电镜可视化特征、核磁共振孔隙结构观测以及物性的变化，揭示渗吸对页岩微观孔隙结构及其物性的影响机理。研究结果表明：①水相渗吸作用使页岩产生微裂缝和裂缝，从而改变页岩孔隙结构；②孔隙度明显改善的页岩样品中，大孔所占比例上升，表明水相渗吸作用会使页岩孔隙空间增大；③渗吸能力与页岩的孔隙度、渗透率呈正相关，且页岩物性在渗吸后改善明显。此外，发现时间指数可定量表征渗吸对页岩孔喉连通性的影响。

关键词: 页岩气藏, 裂缝, 水相渗吸, 物化作用, 微观孔隙结构

Abstract:

Shale gas reservoirs, which develope micro-nano pore throats and fractures, have high clay mineral content, and strong heterogeneity of porosity. Therefore, large-scale hydraulic fracturing is usually needed to realize the effective exploitation. In the process of hydraulic fracturing, the spontaneous imbibition of the water phase will trigger a series of physical and chemical effects on the shale gas reservoir, changing the pore structures, physical and chemical properties of shale gas reservoirs, thereby affecting the production of shale gas. In order to further clarify the influence mechanism of water phase imbibition in shale gas reservoirs, multiple repetitive imbibition experiments were carried out. Based on the changes in rock sample quality caused by mineral dissolution, the visual characteristics of samples from scanning electron microscope, the observation of nuclear magnetic resonance pore structures, and the change of physical properties, the impact of imbibition on the microscopic pore structure, permeability and porosity of shale are revealed. The results show that: ① Water imbibition causes fractures in shale, thus changing the pore structure; ② The proportion of macropores increases in shale samples with significantly improved porosity, which indicates that water imbibition will increase the pore space in shale; ③ The imbibition capacity is positively correlated with the porosity and permeability of shale, and the physical properties of shale are significantly improved after imbibition. In addition, the time index is found to be able to quantitatively characterize the influence of imbibition on the pore-throat connectivity of shale.

Key words: shale gas reservoir, fracture, water phase imbibition, physical and chemical effect, microscope structure of pore

中图分类号:

TE341

李颖,李茂茂,李海涛,于皓,张启辉,罗红文. 水相渗吸对页岩储层的物化作用机理研究[J]. 油气藏评价与开发, 2023, 13(1): 64-73.

LI Ying,LI Maomao,LI Haitao,YU Hao,ZHANG Qihui,LUO Hongwen. Physicochemical mechanism of water phase imbibition in shale reservoirs[J]. Reservoir Evaluation and Development, 2023, 13(1): 64-73.

图/表 18

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表2

表3

表4

图1

图2

图3

图4

图5

图6

图7

图8

图9

图10

图11

图12

表5

不同尺寸页岩样品参数与时间指数"

编号	长度（cm）	直径（cm）	$A c M$ （cm²/g）	n
CN1-1-1	1.01	2.53	0.41	0.365
CN1-2	3.04	2.54	0.13	0.344
CN2-1-1	1.00	2.53	0.40	0.336
CN2-2	1.93	2.52	0.20	0.360
YN-1-1	0.84	2.51	0.45	0.560
YN-2	1.78	2.53	0.21	0.470
CQ-1-1	0.84	2.54	0.44	0.402
CQ-3	2.88	2.55	0.13	0.378

表5

表6

重复渗吸页岩样品时间指数变化"

编号	长度（cm）	直径（cm）	$A c M$ （cm²/g）	n
CN1-1-2	1.01	2.53	0.41	0.429
CN2-1-2	1.00	2.53	0.40	0.440
YN-1-2	0.84	2.51	0.45	0.630
CQ-1-2	0.84	2.54	0.44	0.540

表6

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编号	形状	体积（cm³）	质量（g）	边界条件	微观孔隙结构观测方法
CN1小岩块	近似长方体	约0.4	1.081 8	AFO	SEM
CN2小岩块		约0.4	1.124 4	AFO	SEM
YN小岩块		约0.3	0.676 6	AFO	SEM
CQ小岩块		约0.4	1.054 4	AFO	SEM

编号	单位岩石质量渗吸量（%）	黏土矿物含量（%）	孔隙度（%）	渗透率（10^-3μm²）	长度（cm）
CN1-1-1	2.163	15.8	3.98	0.000 415	1.01
CN2-1-1	1.460	14.4	3.29	0.000 113	1.00
YN-1-1	1.902	35.1	3.48	0.000 338	0.84
CQ-1-1	0.928	29.3	1.92	0.000 055	0.84