煤岩体积压裂脆性评价研究

摘要/Abstract

摘要：

水力压裂是煤层气开发的主要手段,通过压裂可以在煤层中形成有效的甲烷渗流通道,而体积压裂不仅能够在煤层中形成渗流通道,还能通过复杂裂缝的切割增大甲烷的解吸扩散面积,提高单井产量。脆性指数是体积压裂实施评价的关键参数,因此,基于煤岩和页岩的应力应变曲线,借助应变能密度的概念,分析了煤岩和页岩的脆性指数。页岩的应变能密度与脆性指数计算结果表明,页岩脆性指数越高,应变能密度越低。在页岩脆性指数的计算方法上,结合应变能密度与最小能量原理,提出了煤岩脆性指数的计算方法,并通过修正得到了用于表征煤岩脆性破坏能力和评价煤层压后产生多裂缝能力的煤岩脆性指数。最后,结合现场6口压裂井的数据进行了实例分析,结果表明,煤岩脆性指数与单位改造体积具有强相关性,即脆性指数越高,单位压裂液的煤层改造体积越大。该方法可以用于煤岩体积压裂设计,指导煤层气的开发。

关键词: 体积压裂, 煤岩力学特征, 应变能密度, 脆性指数, 多裂缝

Abstract:

The hydraulic fracturing is a major means of the coalbed methane（CBM） exploitation, and the effective channels of the methane seepage can be formed in the coal seams by this means. The stimulated reservoir volume（SRV） can not only help the coal seams form the seepage channels, but also increase the desorption-diffusion areas of the methane and improve the production of the single well by formed the complicated fractures. The brittleness index is one of the key parameters for evaluating the SRV implement, therefore, based on the stress-strain curves of the coal and shale, it is analyzed with the help of the strain-energy density. The higher the brittleness index of the shale is, the lower the strain-energy density will be. Based on the calculation method of the brittleness index of the shale, the calculation method of the coal brittleness index that combines with the strain-energy density and minimum energy principle is put forward, and the modified brittleness index of the coal is obtained, which can be used for the characterization of the coal brittle failure and evaluation of the fracture formation after fracturing. Finally, the analysis of the calculation results and data of 6 fracturing wells, indicates that the strong correlation between the coal brittleness index and stimulated volume, which means that the higher the brittleness index is, the larger the stimulated volume of unit fracturing fluid in the coal seams will be. This method can be applied to design the SRV of the coal seams and guide the exploitation of CBM.

Key words: stimulated reservoir volume（SRV）, mechanical property of coal, strain energy density, brittleness index, multifractures

中图分类号:

TE357

路艳军,杨兆中,ShelepovVV等. 煤岩体积压裂脆性评价研究[J]. 油气藏评价与开发, 2018, 8(1): 64-70.

Yanjun Lu,Zhaozhong Yang,V V Shelepov, et al. Evaluation and research of brittleness on simulated reservoir volume in coal[J]. Reservoir Evaluation and Development, 2018, 8(1): 64-70.

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岩石类型	峰值压力/MPa	最大轴向应变	杨氏模量/MPa	泊松比	应变能密度/（mJ·mm^-3）	脆性指数,%
页岩B	99	0.002 4	47 892	0.19	0.118 8	69.07
页岩D	179	0.006 4	35 260	0.31	0.572 8	36.04
页岩E	172	0.006 3	36 260	0.3	0.541 8	38.76
页岩H	138	0.003 7	44 195	0.27	0.255 3	50.43
煤岩A	32.5	0.009 3	2 668.7	0.246	0.152 1	48.21
煤岩B	18.5	0.008 3	2 713.3	0.473	0.076 6	16.10
煤岩E	36.2	0.011 1	3 672.5	0.261	0.200 9	53.23
煤岩F	25	0.009 4	2 471.3	0.324	0.117 8	35.65