摘要
目前煤层气单井主要通过水力压裂技术来提高产量,但水力压裂技术会导致煤层裂缝出现分区现象,在有效应力作用下不同裂缝分区的渗流特征将直接影响煤层气抽采效果。为了更好地研究有效应力对不同裂缝分区渗流特征的影响,以沁水盆地煤样为例,设计了完整煤样、微裂缝煤样和贯穿裂缝煤样的串、并联多腔体试验方法,分析了水力压裂后煤层气的横向沿区渗流和纵向跨区渗流,构建了有效应力影响下的不同损伤煤岩体串、并联渗透率模型,分析了有效应力恢复过程中水力压裂不同致裂分区的渗流特征,并预测了不同致裂深度和扰动范围下的煤层总体渗透性。研究结果表明:(1)随着有效应力的恢复,串、并联试验的总流量均呈现负指数形式的衰退;(2)在并联试验中,穿过完整煤样的流量占比极少,随着有效应力的恢复,穿过微裂缝煤样的流量占比逐渐增加,而贯穿裂缝煤样的流量逐渐减小,并逐渐趋于相等;(3)纵向渗流总渗透率小于横向渗流,纵向渗流总渗透性的变化受完整煤样的渗透性影响较大,而横向渗流总渗透性取决于贯穿裂缝煤样渗透性;(4)基于横纵向渗透率的大小,可以将煤层气产期曲线划分为单峰型与双峰型。结论认为,提高水力裂缝深度与射孔孔眼周围裂缝宽度有利于提高煤层气的抽采量,该认识可以为煤层气水力压裂参数设计提供参考,有助于推动煤层气的效益开发。
Hydraulic fracturing is dominantly used to improve the production of coalbed methane(CBM) well,but it may induce fracture zones in the coal seams.Due to the effective stress,the flow behaviors in fracture zones have direct impacts on the effectiveness of CBM extraction.To determine such impacts,taking the coal samples from the Qinshui Basin as examples,this paper designs a serial/parallel multi-cavity test using intact coal samples,microfractured coal samples and fracture-penetrated coal samples to investigate the transverse CBM flow along zones and longitudinal CBM flow crossing zones after hydraulic fracturing.A permeability model of different serial-parallel damaged coal rocks under the influence of effective stress is established to analyze the flow behaviors in fracture zones induced by hydraulic fracturing under effective stress recovery conditions and predict the overall permeability of coal seams at different fracturing depths and in different disturbance ranges.The findings demonstrate that the total flow exhibits a negative exponential pattern of drop with the restoration of effective stress in both serial and parallel tests.In the parallel tests,the percentage of flow through the intact coal samples is very low,the percentage of flow through the microfractured coal samples gradually rises when the effective stress is restored,and the percentage of flow through the fracture-penetrated coal samples progressively falls until it becomes equal.Longitudinal flow shows a smaller total permeability than transverse flow.The total permeability of longitudinal flow is greatly affected by the permeability of intact coal samples,while the total permeability of transverse flow is dependent on the permeability of fracture-penetrated coal samples.Based on the size of transverse/longitudinal permeability,the CBM production profiles can be divided into monomodal and bimodal curves.It is concluded that increasing the hydraulic fracture depth and fracture width around the borehole is conducive to improving the gas extraction.This offers a reference for designing the parameters of hydraulic fracturing in CBM reservoirs to promote the beneficial extraction of CBM.
作者
张村
刘晨熙
王永乐
徐伍艳
赵毅鑫
宋子玉
ZHANG Cun;LIU Chenxi;WANG Yongle;XU Wuyan;ZHAO Yixin;SONG Ziyu(Beijing Key Laboratory for Precise Mining of Intergrown Energy and Resources//China University of Mining and Technology-Beijing,Beijing 100083,China;Joint National-Local Engineering Research Centre for Safe and Precise Coal Mining,Anhui University of Science and Technology,Huainan,Anhui 232001,China)
出处
《天然气工业》
EI
CAS
CSCD
北大核心
2024年第3期152-163,共12页
Natural Gas Industry
基金
国家自然科学基金资助项目“深部复杂应力条件下煤储层多尺度岩石力学性质及其控制因素研究”(编号:U1910206)
“采空区残留煤柱阻流机理与受载水浸灾变机制”(编号:52104155)
北京市自然科学基金项目“京津冀资源枯竭型矿井采空区储水机理与净水能力”(编号:8212032)
中国博士后基金项目“中国博士后科学基金第73批面上资助”(编号:2023M733778)。
关键词
煤层气
水力压裂
渗透率
损伤分区
有效应力
裂缝压缩性
产能影响因素
沁水盆地
CBM
Hydraulic fracturing
Permeability
Damage zone
Effective stress
Fracture compressibility
Factor affecting productivity
Qinshui Basin
