Fluid-Solid Coupling Physical Experiments and Their Implications for Fracturing Stimulations of Shale Gas Reservoirs
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摘要: 页岩压裂改造过程中渗透率变化和压裂缝扩展的机理对页岩气开发压裂工程设计具有重要意义，通过页岩岩心首次加载-卸载-二次加载流-固耦合物理模拟实验和二次加载实验后岩心微米CT成像分析，揭示出两个重要现象：(1) 首次加载-卸载-二次加载过程，有助于提高岩心的渗透率；(2) 在二次加载过程中，岩心渗透率随轴压增加出现增加或降低不同的现象，分别对应压裂缝的有序化和方向性扩展或无序化和局部糜棱化扩展.实验获得的认识对页岩储层压裂改造有两条启示：(1) 泵入-停泵-再泵入循环压裂有助于改善页岩气储层的渗透率；(2) 对天然裂缝发育的页岩储层，压裂规模的针对性设计十分关键.Abstract: The mechanisms of permeability variations and fracture extension are essential for hydraulic fracturing design in shale gas exploitation. Based on fluid-solid coupling physical experiments and Micro-CT imaging analysis, this study reveals two important phenomena: (1) loading-unloading-reloading cycle has an effect on increasing the permeability of shale samples, (2) during the reloading process, the permeability of shale samples show different trends with increasing axial pressure. In the permeability increasing case with increasing axial pressure, the fractures are produced directionally and orderly. In another case, the fractures are produced disorderly and locally mylonitic. The results show that (1) pumping-intermission-repumping multi-cycles could help modify the stimulation effect of in-site fracturing operations, and (2) hydraulic fracturing volume should be appropriately controlled for naturally fractured shale gas reservoirs.
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Key words:
- shale gas /
- fluid-solid coupling effect /
- physical experiment /
- permeability /
- CT imaging /
- fracturing stimulation /
- petroleum geology
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图 1 黔江2井、龙山1井井位和区域构造
Fig. 1. Structure sketch and the locations of wells Qianjiang 2 and Longshan 1
图 2 流-固耦合实验页岩岩心照片
a.含天然缝岩心QJ2-9-1；b.不含天然缝岩心LS1-2-3；c.含天然缝岩心QJ2-14
Fig. 2. Photos of shale core samples prepared for fluid-solid coupling physical experiments
图 3 流-固耦合物理模拟实验流程
①、②、③、④ 为应变传感器编号；P1、P2为气体压力测量点；T1、T2为温度测量点
Fig. 3. Flowing chart of fluid-solid coupling physical experiments
图 4 页岩岩心二次加载渗透率-轴压实验关系
a.含天然裂缝岩心QJ2-9-1；b.不含天然裂缝岩心LS1-2-3
Fig. 4. Relationship between permeability and axial pressure gained from the second-time loading for shale samples
图 5 二次加载试验后页岩岩心切片微米CT扫面图像
a.含天然裂缝岩心QJ2-9-1；b.含天然裂缝岩心QJ2-14；c.不含天然裂缝岩心LS1-2-3
Fig. 5. Micro-CT images of the shale samples after experiments
表 1 流-固耦合物理模拟实验页岩岩心描述表
Table 1. Shale core sample descriptions for fluid-solid coupling physical experiments
井号 岩心编号 取样深度(m) 均深(m) 层位 岩心描述 黔江2井 QJ2-9-1 695.79~698.51 697.15 志留系龙马溪组黑色页岩段 灰黑色页岩，结构致密，含天然裂缝，实验后因岩心破碎，未做岩矿分析 龙山1井 LS1-2-3 939.50~942.50 941.00 寒武系筇竹寺组黑色页岩 暗黑色，结构致密，不含天然裂缝，脆性矿物石英含量为49.41%，长石含量为11.81%，方解石+白云石含量为0.92% 黔江2井 QJ2-14 724.29~728.80 726.55 志留系龙马溪组黑色页岩段 暗黑色页岩，结构致密，含天然裂缝，脆性矿物石英含量为29.55%，长石含量为9.83%，方解石+白云石含量为4.38% 
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表 2 含天然缝岩心QJ2-9-1首次加载实验数据
Table 2. Experiment data of first-time loading for naturally fractured shale sample QJ2-9-1
轴压(MPa) 围压(MPa) 时间(h) 入口气压(MPa) 出口气压(MPa) 平均流量(mL/s) 渗透率(mD) 8.00 5.00 0.53 1.580 0.1 0.69 0.08 12.00 5.00 0.72 1.414 0.1 0.73 0.09 16.00 5.00 0.94 1.427 0.1 0.65 0.08 20.00 5.00 4.80 1.480 0.1 - 因实验控制问题，未测渗透率 24.00 5.00 5.31 2.000 0.1 - 30.00 5.00 5.84 2.050 0.1 - 36.00 5.00 6.31 2.050 0.1 - 44.00 5.00 6.81 2.040 0.1 - 52.00 5.00 8.54 2.030 0.1 - 62.00 5.00 9.04 2.030 0.1 - 72.00 5.00 9.70 2.030 0.1 -
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表 3 含天然缝岩心QJ2-9-1二次加载实验数据
Table 3. Experiment data records of second-time loading for naturally fractured shale sample QJ2-9-1
轴压(MPa) 围压(MPa) 时间(h) 入口气压(MPa) 出口气压(MPa) 平均流量(mL/s) 渗透率(mD) 8.00 5.00 0.52 - 0.10 - - 18.00 5.00 0.93 0.79 0.10 0.48 0.19 28.00 5.00 5.30 0.82 0.10 0.45 0.17 38.00 5.00 6.31 0.82 0.10 0.36 0.13 48.00 5.00 6.87 0.83 0.10 0.33 0.12 58.00 5.00 8.54 0.83 0.10 0.31 0.11 68.00 5.00 9.01 0.83 0.10 0.32 0.11 78.00 5.00 9.71 0.83 0.10 0.30 0.11
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表 4 不含天然缝岩心LS1-2-3首次加载实验数据
Table 4. Experiment data records of first-time loading for naturally un-fractured shale sample LS1-2-3
轴压(MPa) 围压(MPa) 时间(h) 入口气压(MPa) 出口气压(MPa) 平均流量(mL/s) 渗透率(mD) 8.00 5.00 0.55 2.98 0.1 无流量 0 10.00 5.00 1.22 2.98 0.1 无流量 0 12.00 5.00 2.03 2.98 0.1 无流量 0 14.00 5.00 2.74 2.98 0.1 无流量 0 16.00 5.00 3.47 2.98 0.1 无流量 0 20.00 5.00 3.70 2.98 0.1 无流量 0 24.00 5.00 4.20 2.98 0.1 无流量 0 28.00 5.00 4.63 2.98 0.1 无流量 0 32.00 5.00 4.74 2.98 0.1 无流量 0 38.00 5.00 5.14 2.98 0.1 无流量 0 44.00 5.00 5.94 2.98 0.1 无流量 0 50.00 5.00 6.36 2.98 0.1 无流量 0 56.00 5.00 6.55 2.98 0.1 无流量 0 62.00 5.00 6.88 2.98 0.1 无流量 0 68.00 5.00 7.08 2.98 0.1 无流量 0
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表 5 不含天然缝岩心LS1-2-3岩心二次加载实验数据
Table 5. Experiment data records of second-time loading for naturally un-fractured shale sample LS1-2-3
轴压(MPa) 围压(MPa) 时间(h) 入口气压(MPa) 出口气压(MPa) 平均流量(mL/s) 渗透率(mD) 8.00 5.00 0.06 1.45 0.10 0.76 0.10 18.00 5.00 0.50 1.43 0.10 1.00 0.14 33.00 5.00 0.65 1.42 0.10 1.36 0.19 48.00 5.00 0.77 1.41 0.10 1.85 0.26 63.00 5.00 0.89 1.40 0.10 3.08 0.44 78.00 5.00 1.00 1.05 0.10 2.73 0.66 93.00 5.00 1.13 0.61 0.10 1.85 1.18
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表 6 含天然缝岩心QJ2-14首次-二次加载实验数据
Table 6. Experiment data records for naturally fractured shale sample QJ2-14
加载情况 轴压(MPa) 围压(MPa) 时间(h) 入口气压(MPa) 出口气压(MPa) 平均流量(mL/s) 渗透率(mD) 首次加载 8.00 5.00 0.08 0.95 0.10 0.29 0.08 10.00 5.00 0.74 0.92 0.10 0.15 0.04 20.00 5.00 0.93 0.92 0.10 1.76 0.51 30.00 5.00 1.05 0.93 0.10 2.51 0.71 40.00 5.00 1.28 0.94 0.10 3.33 0.92 50.00 5.00 1.68 0.94 0.10 3.45 0.95 60.00 5.00 2.14 0.95 0.10 3.39 0.92 二次加载 8.00 5.00 0.06 1.01 0.10 3.64 0.88 10.00 5.00 0.09 1.01 0.10 4.03 0.98 20.00 5.00 0.22 1.02 0.10 4.15 0.99 30.00 5.00 0.36 1.01 0.10 4.56 1.10 40.00 5.00 0.45 1.01 0.10 6.90 1.67 50.00 5.00 0.53 1.00 0.10 9.38 2.31 60.00 5.00 0.59 1.00 0.10 12.45 3.07
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