彭水地区龙马溪组页岩渗吸规律及渗吸动态分布

doi:10.19596/j.cnki.1001-246x.8394

摘要/Abstract

摘要：

渗吸作为压裂液在储层中的主要吸收方式, 是提高页岩气产能的重要驱动力。以重庆市彭水地区龙马溪组页岩为研究对象, 依次进行毛管力测试、不同条件下的渗吸实验及核磁共振实验。结果表明: ①页岩的渗透率与孔隙度极低, 以微孔和小孔为主, 基本无大孔, 孔隙结构较差; ②页岩渗吸过程分为三个阶段, 随着压力和温度的升高, 渗吸效果增强, 破胶压裂液的渗吸效果略强于未破胶压裂液, 表面活性剂和KCl溶液可以降低页岩渗吸能力; ③页岩渗吸的核磁共振T₂谱具有明显的双峰特征, 渗吸过程中, 中大的孔隙和裂缝在初期阶段就被液体瞬间充满, 极微的孔隙和裂缝首先被充填, 随后液体进入稍大的微孔隙和微裂缝, 在渗吸过程中页岩表面产生大量的微裂缝。

关键词: 页岩, 渗吸, 核磁共振, 孔隙结构, 影响因素

Abstract:

As the main absorption mode of fracturing fluid in reservoir, imbibition is an important driving force to improve shale gas productivity. In this paper, the Longmaxi formation shale in Pengshui area of Chongqing is studied. Mercury intrusion porosimetry, imbibition under different conditions and NMR tests were carried out successively. It shows that: ① The permeability and porosity of shale are very low, mainly micropores and mesopcres, almost no macropores, and the pore structure is poor; ② The process of shale imbibition can be divided into three stages. With the increase of pressure and temperature, imbibition behavior is enhanced. The imbibition effect of gel breaking fracturing fluid is slightly stronger than that of non-gel breaking fracturing fluid. Surfactant and KCl solution can reduce the imbibition ability of shale; ③ In the process of imbibition, the medium and large pores and fractures are filled with liquid in the initial stage, while the very small pores and fractures are filled first, and then the liquid enters into the slightly larger micropores and microcracks, resulting in a large number of microcracks on the surface of shale.

Key words: shale, imbibition, nuclear magnetic resonance, pore structure, influence factor

中图分类号:

TE371

朱云轩, 李治平. 彭水地区龙马溪组页岩渗吸规律及渗吸动态分布[J]. 计算物理, 2021, 38(5): 555-564.

Yunxuan ZHU, Zhiping LI. Imbibition Behavior and Fluid Dynamic Distribution of Longmaxi Formation Shale in Pengshui Area[J]. Chinese Journal of Computational Physics, 2021, 38(5): 555-564.

图/表 19

图1 彭水地区龙马溪组页岩岩心

Fig.1 Shale samples of Longmaxi formation in Pengshui area

表1 岩心物性资料

Table 1 Petrophysical properties of core samples

岩样编号	直径/cm	长度/cm	密度/(g·cm^-3)	孔隙度/%	渗透率/(10^-3 μm²)
1	2.53	2.72	2.62	3.91	0.007
2	2.60	2.68	2.62	3.99	0.007
3	2.55	2.72	2.60	3.87	0.005
4	2.59	2.67	2.57	3.75	0.005
5	2.53	2.71	2.64	4.25	0.006
6	2.50	2.69	2.63	3.80	0.006
7	2.54	2.70	2.63	3.77	0.007
8	2.51	2.66	2.56	3.89	0.006

图2 渗吸体积法实验装置示意图

Fig.2 Experimental device of imbibition volume method

图3 EM-2型高压渗吸仪

Fig.3 EM-2 high pressure imbition instrument

图4 核磁共振岩心分析仪

Fig.4 Nuclear magnetic resonance core analyzer

表2 毛管力曲线测试结果

Table 2 Test results of capillary pressure curves

岩样编号	半径均值/μm	仪器最大退出效率/%	排驱压力/MPa	汞饱和度/%		孔喉半径/μm			孔喉分布		渗透率分布
岩样编号	半径均值/μm	仪器最大退出效率/%	排驱压力/MPa	最大	最终剩余	最大	平均	中值	峰位/μm	峰值/%	峰位/μm	峰值/%
1	0.015	91.772	13.775	97.955	8.060	0.053	0.013	0.009	0.006	18.909	0.040	56.847
2	0.012	88.374	13.776	95.751	11.132	0.053	0.012	0.008	0.006	21.117	0.040	41.743

图5 岩心毛管压力曲线

Fig.5 Capillary pressure curves of samples

图6 岩心孔喉分布

Fig.6 Distribution of core pore throat

图7 不同压力下渗吸量与渗吸时间关系

Fig.7 Relations between the imbibition amount and time under different pressures

图8 不同压力下渗吸量与渗吸时间的关系

Fig.8 Relations between imbibition amount and time under different pressures

图9 不同压力下渗吸速率与渗吸时间的关系

Fig.9 Relations between imbibition speed and time under different pressures

图10 不同温度下渗吸量/渗吸速率与渗吸时间的关系

Fig.10 Relations between imbibition amount/imbibition speed and time under different temperatures

表3 不同压裂液的渗吸结果

Table 3 Imbibition results of different fracturing fluids

渗吸条件	渗吸量/ml	初始渗吸速率/(ml·h^-1)
0.1 MPa未破胶	1.3	0.23
0.1 MPa破胶	1.35	0.28
5 MPa未破胶	1.4	0.26
5 MPa破胶	1.43	0.32
10 MPa未破胶	1.48	0.31
10 MPa破胶	1.52	0.35

图11 不同压裂液渗吸量/渗吸速率与渗吸时间的关系

Fig.11 Relations between imbibition amount/imbibition speed and time of different fracturing fluids

图12 页岩岩心表面活性剂处理前后的润湿角(a)处理前; (b)处理后

Fig.12 Wetting angle of shale core before and after surfactant treatment (a) before treatment; (b) after treatment

图13 不同液体对自吸能力的影响

Fig.13 Influence of different liquids on spontaneous-imbibition ability

图14 不同渗吸时间下的核磁共振T2谱

Fig.14 NMR T2 spectra under different imbibition times

图15 不同压力下的核磁共振T2谱

Fig.15 NMR T2 spectra under different pressures

图16 不同温度下的核磁共振T2谱

Fig.16 NMR T2 spectra under different temperatures

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