石油学报 ›› 2017, Vol. 38 ›› Issue (7): 830-839.DOI: 10.7623/syxb201707010

• 石油工程 • 上一篇    下一篇

致密砂岩多段分簇压裂中孔隙压力场对多裂缝扩展的影响

周大伟, 张广清, 刘志斌, 董昊然   

  1. 中国石油大学石油工程学院 北京 102249
  • 收稿日期:2016-08-13 修回日期:2017-04-28 出版日期:2017-07-25 发布日期:2017-08-10
  • 通讯作者: 张广清,男,1975年7月生,1996年获石油大学(华东)学士学位,2002年获石油大学(北京)博士学位,现为中国石油大学(北京)教授、博士生导师,主要从事石油工程岩石力学与岩土工程的研究。Email:zhangguangqing@cup.edu.cn
  • 作者简介:周大伟,男,1988年10月生,2013年获中国石油大学(华东)学士学位,现为中国石油大学(北京)博士研究生,主要从事石油工程岩石力学研究。Email:zhoudawei_petro@126.com
  • 基金资助:

    国家自然科学基金优秀青年科学基金项目(No.51322404)资助。

Influences of pore-pressure field on multi-fracture propagation during the multi-stage cluster fracturing of tight sandstone

Zhou Dawei, Zhang Guangqing, Liu Zhibin, Dong Haoran   

  1. College of Petroleum Engineering, China University of Petroleum, Beijing 102249, China
  • Received:2016-08-13 Revised:2017-04-28 Online:2017-07-25 Published:2017-08-10

摘要:

为了研究致密砂岩多段分簇压裂中孔隙压力场对多裂缝扩展的影响,采用300 mm×300 mm×600 mm天然砂岩进行真三轴水力压裂实验,实验过程中采用2套压裂液注入系统分别独立控制2条水力裂缝,实验后将试件连续切片分析实验结果,同时采用三维流固耦合数值模拟方法研究孔隙压力场对水力裂缝扩展的影响。结果表明:在致密砂岩压裂中,由于孔隙压力场的存在,无论是簇内裂缝还是簇间裂缝扩展,当缝间距与裂缝半长的比值较小时,裂缝之间表现为相互吸引;当缝间距与裂缝半长的比值较大时,裂缝之间的相互影响较弱,多裂缝之间未出现相互排斥现象;除缝内净压力、缝间距、应力差外,裂缝周围孔隙压力场也是影响多裂缝扩展的重要因素;孔隙压力的增大减小了有效应力,岩石更容易发生剪切破坏,从而加速了裂缝的非平面、非对称双翼扩展;现场致密砂岩多段分簇压裂应增大簇间和簇内射孔间距,可避免压裂液滤失导致裂缝长度的减小,增大储层的改造体积。

关键词: 多段分簇射孔压裂, 多裂缝扩展, 相互吸引, 孔隙压力场, 致密砂岩

Abstract:

To study the influences of pore-pressure field on multi-fracture propagation during the multi-stage cluster fracturing of tight sandstone, the natural sandstones of 300 mm×300 mm×600 mm were used for true tri-axial hydraulic fracturing experiment. In the experiment process, two sets of fracturing fluid pumping system were employed to independently control two hydraulic fractures. After the experiment, the specimens were sliced consecutively to analyze the experimental results. Meanwhile, the 3D coupled fluid-solid numerical simulation method was developed to study the influences of pore-pressure field on hydraulic fracture propagation. The results show that because of the existence of pore-pressure field in the fracturing process of tight sandstone, when the ratio of fracture spacing to fracture half-length is small, the fractures show mutual attraction when intra-cluster fracture or inter-cluster fracture are expanded. When the ratio of fracture spacing to fracture half-length is large, the interaction between fractures is weak, and no rejection occurs among multi-fractures. Beside intra-fracture net pressure, fracture spacing and stress difference, the pore-pressure field around fractures also plays a vital role in affecting multi-fracture propagation. The increase of pore pressure can reduce the effective stress, and thus is more likely to cause rock shear failures in sandstone; meanwhile, the non-planar and asymmetric bi-wing fracture expansion is accelarated. For the multi-stage cluster fracturing of tight sandstone, the inter-cluster and intra-cluster perforation spacing should be increased to avoid the reduction of fracture length caused by the filtration of fracturing fluid and increase the reservoir reformation volume.

Key words: multi-stage cluster perforation fracturing, multi-fractures propagation, mutual attraction, pore-pressure field, tight sandstone

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