基于无量纲裂缝导流能力的煤储层压裂效果分析

Analysis of Hydraulic Fracturing Effect on Coal Reservoir Based on Dimensionless Fracture Conductivity

煤储层原位渗透率普遍偏低,通常需用水力压裂造缝方式改善煤储层的渗透性能,但其效果的定量评价长期未能有效解决。本文以沁水盆地南部郑庄区块16口新井为例,采用有限导流能力裂缝模型拟合压裂造缝后关井阶段的压降曲线,计算了裂缝的无量纲导流能力(CfD),实现了压裂效果的定量化分析,并讨论了其地质影响因素。结果显示,CfD值越大,压裂效果越好;煤岩杨氏模量、剪切模量和体积模量的增加,裂缝无量纲导流能力有减小的趋势,但与煤岩泊松比大小无关。煤储层纵向上的力学非均质性对裂缝无量纲导流能力也有影响,随着非均质程度的增加,无量纲导流能力逐渐增加;当非均质性达到一定程度时,无量纲导流能力变低。

Hydraulic fracturing was usually used to improve coal reservoir permeability which is generally low in situ, but a valid method for the quantitative evaluation of the fracturing effect has not been set up. Based on the finite-conductivity fracture model and in a case of the 16 coalbed methane （CBM） wells in the Zhengzhuang block of the Qinshui basin, the dimensionless fracture conductivity （Crp） was emnputed with the history matching of the pressure-drop curves during the well shut through which the quantitative evaluation of the fracturing effect was achieved. The geologic controls of the effect were analyzed. Results showed that the higher Cfp is the better fracturing effect. Cfp trends to reduce with increasing the Young＇s, shear and bulk moduluses but is poorly relevant to the Poisson＇ s ratio. In addition, Cfp is also influenced by vertical mechanical anisotropy of coal reservoir and raises with the increase of the anisotropy, but reduces once the anisotropy incereases to a certain extent.