摘要
为优化煤层气井排采降压速度,提出了有效应力加载速度敏感性概念,设计并开展了室内实验和现场试验,证实有效应力加载速度敏感性的存在,建立相应的数学模型,提出应力加载速度敏感性评价指标,并分析了应力加载速度敏感性和应力敏感性对渗透率损害率的贡献。结果表明,应力加载速度敏感性能够有效地评价有效应力加载速度对煤层渗透率的损害程度;有效应力增幅相同时,有效应力加载速度越快,渗透率下降幅度越大,渗透率损害率越大,应力加载速度为2 MPa/d时的渗透率损害率比0.5 MPa/d时增加43%以上,证实应力加载速度对煤样渗透率存在损害且非常明显;现场试验和室内实验均进一步揭示煤储层具有明显的应力加载速度敏感性;同一煤样应力敏感性系数随有效应力加载速度增加而增加,且2者呈幂函数关系,据此建立了应力加载速度敏感性的数学模型,实现应力加载速度敏感性的定量表征;应力加载速度敏感性的强弱通过应力加载速度渗透率损害系数评价,其在数值上等于煤样应力加载速度与对应的渗透率损害率数据线性回归得到的直线斜率n,其值越大,煤岩应力加载速度敏感性越强;有效应力加载过程对煤样渗透率的损害率由单纯有效应力增加造成的渗透率损害率和单纯应力加载速度增加而导致的渗透率损害率组成。结果表明,应力加载速度造成的渗透率损害率占比随着应力加载速度增加而持续增加,其占比甚至可以达到50%以上,揭示了在煤层气井排采降压过程中,尽可能降低排采降压速度能够最大限度降低由于应力加载速度造成的渗透率损害率。
In order to optimize the depressurization rate for the drainage of Coalbed Methane(CBM)wells,the concept of effective stress uploading rate sensitivity is proposed,and the indoor experiments and pilot tests are carried out to confirm the existence of the effective stress uploading rate sensitivity.The mathematical model and the corresponding evaluation index of the effective stress uploading rate sensitivity are established.The results show that the stress uploading rate sensitivity can effectively evaluate the damage degree of the permeability of coal seam by effective stress uploading rate.When the effective stress increases at the same range,the faster the effective stress uploading rate is,the greater the permeability decreases,and the greater the permeability damage rate is.The permeability damage degree,when the stress uploading rate is 2 MPa/d,is 43%more than that when the stress uploading rate is 0.5 MPa/d,which confirms that the stress uploading rate has obvious damage to the permeability of the coal sample.The results of pilot test are consistent with that of the laboratory experiments,which further reveals the existence of the stress uploading rate sensitivity for coal reservoir.For certain sample,the stress sensitivity coefficient increases with the increase of the effective stress uploading rate,that is,the greater the stress uploading rate is,the greater the stress sensitivity coefficient is,and there exists a power function relationship between the stress uploading rate and the stress sensitivity coefficient.Therefore,the mathematical model of the stress uploading rate sensitivity is established to realize the quantitative characterization of the stress uploading rate sensitivity.The extent of stress uploading rate sensitivity can be evaluated by the permeability damage coefficient of stress uploading rate sensitivity,which is equal to the value of slope of the linear regression by stress uploading speed versus corresponding permeability damage rate,and the greater the permeability damage coefficient is,the stronger the stress uploading rate sensitivity is.The permeability damage rate during the effective stress loading process consists of the damage rate caused by the increase of the effective stress and that by the increase of the effective stress uploading rate.The results show that the damage rate caused by the increase of the effective stress uploading rate increases with the increase of the uploading rate,and its proportion can reach more than 50%,which reveals that during the process of drainage of CBM well,the reduction of the depressurization rate as far as possible can minimize the permeability damage caused by stress uploading rate sensitivity.
作者
胡秋嘉
贾慧敏
樊彬
毛崇昊
张庆
张先敏
刘春春
覃蒙扶
HU Qiujia;JIA Huimin;FAN Bin;MAO Chonghao;ZHANG Qing;ZHANG Xianmin;LIU Chunchun;QIN Mengfu(CBM Branch Company,Huabei Oilfield of Petrochina,Changzhi 046000,China;School of Petroleum Engineering,China University of Petroleum(East China),Qingdao 266580,China)
出处
《煤炭学报》
EI
CAS
CSCD
北大核心
2022年第S01期204-213,共10页
Journal of China Coal Society
基金
国家科技重大专项资助项目(2017ZX05064)
中国石油天然气股份有限公司重大科技专项资助项目(2017E-1405)
关键词
煤层气
应力加载速度敏感性
应力敏感性
数学模型
应力加载速度渗透率损害系数
coalbed methane
stress uploading rate sensitivity
stress sensitivity
mathematical model
permeability damage coefficient of stress uploading rate
