水岩反应中泥质夹层生成固相微粒的实验研究

Experimental research on the generation of solid fines from muddy intercalation in water-rock reaction

在煤储层地质条件和煤层气开发工程的双重控制下,以煤粉为主的固相微粒生成和运移对煤层气井连续稳定排采的制约作用尤为严重。为查明复杂煤层结构对煤层气开发中固相微粒生成规律的影响,以叠置发育煤层和泥质夹层的岩芯样品为研究对象,应用单相液流岩芯驱替仪,开展了水岩反应物理模拟实验,对比分析了在不同浓度的KCl溶液环境中泥质夹层与煤层生成固相微粒的数量、类型、运移特征及其对玻璃珠层导流能力的伤害程度。结果表明:在相同的物理模拟实验条件下,与煤层相比,泥质夹层在水岩反应中易于生成数量更多、粒径更小的黏土矿物型固相微粒;KCl溶液浓度影响着泥质夹层中固相微粒的产出规律,低浓度的KCl溶液与泥质夹层会发生高强度的水岩反应,从而使固相微粒的生成量和迁移率增大;固相微粒的黏滞状态会伤害玻璃珠层的导流能力,随着溶液浓度升高,固相微粒的生成强度和运移距离减小,渗透率降低幅度的波动变化持续时间相应缩短。结合渭北石炭—二叠纪煤田韩城矿区煤层气开发实践研究认为,以复杂结构煤层为煤层气井排采对象会使煤中夹矸的层数增加、厚度变大、岩性多样和矿物复杂,这将导致泥质夹层等敏感岩层的矿物组分和岩石结构稳定性因水岩反应和应力破坏的综合作用而相应降低,造成煤储层固相微粒的产出类型趋于复杂多样化,使固相微粒的生成强度升高和运移距离增大,进而引起更加严重的储层伤害和频繁发生的设备故障,直接影响着煤层气井排采效果。通过查明煤层气井开发层内夹矸的空间发育特征、敏感矿物类型及其含量,可在钻井、压裂和修井等生产环节中适当使用防膨剂和稳定剂来降低黏土矿物的膨胀分散程度、增强煤岩表面疏水性和提高煤粉在裂隙面的黏附力,以此减少固相微粒的生成量和迁移率,从而有效防治煤储层固相微粒的产出问题。

Under the dual control of coal reservoir geological conditions and CBM development engineering,the generation and migration of solid fines,which mainly are coal fines,has a particularly severe restriction on the continuous and stable production of CBM wells.To identify the impact of complex coal bed texture on the gener-ative rule of solid fines in CBM development,taking the core sample with superimposed coal seam and muddy intercalation as a research object,the physical simulation experiment of water-rock reaction (WRR) was carried out by using single-phase water flow core flooding rig.The amount,types and migration features of solid fines and their damage on glass beads layer (GBL) conductive ability were contrastively analyzed,which were generated separately from muddy intercalation and coal seam with KCl solution of different concentrations.The results show that under the same conditions of physical simulation experiment,muddy intercalation can easily generate more clay mineral solid fines with smaller particle size in WRR compared to coal seam.The concentration of KCl solution affects the rule of solid fines generation from muddy intercalation,high intensity WRR between the KCl solution of low concentration and muddy intercalation can be produced,which causes the increase in the generative amount and migration rate of solid fines.The damage on the conductive ability of GBL can be caused by the cementation and retention of solid fines,with the increase of solution concentration,the generative amount and migration distance of solid fines declines,which reduces the duration of the decrease extent of permeabil-ity fluctuation accordingly.Combined with the research on CBM development practice at Hancheng mining area in Weibei Carboniferous-Permian coal- field,it is concluded that the CBM production in coal seam with complex texture can increase the layers and thickness of parting,diversify its lithology and complicate its mineral compo- nents,which will weaken the stability of mineral composition and rock structure of muddy intercalation and other sensitive rock formations in the combined influence of stress rupture and WRR,lead to the generative types of solid fines in coal reservoir becoming complex and diverse,increase the generative intensity and migration distance of solid fines,and then result in more serious reservoir damage and frequent equipment failures,which directly affects the production of CBM wells.By ascertaining the spatial development characteristics,types and contents of sensitive minerals of parting in CBM development layers,anti-swelling agent and stabilizer can be used properly in drilling,fracturing and workover to reduce the degree of clay mineral expansion and dispersion,increase the surface hydrophobicity of coal and improve the adhesion force of coal fines in the fracture surface,which could reduce the generative amount and migration rate of solid fines and then the issue of solid fines production in coal reservoir can be effectively controlled.