石油学报 ›› 2019, Vol. 40 ›› Issue (S2): 131-140.DOI: 10.7623/syxb2019S2013

• 石油工程 • 上一篇    下一篇

基于线性强化弹塑性疏松砂岩破裂模式

赵少伟1, 马英文1, 刘飞航2, 李海涛2, 张建丰3   

  1. 1. 中海石油(中国)有限公司天津分公司 天津 300450;
    2. 西南石油大学油气藏地质及开发工程国家重点实验室 四川成都 610500;
    3. 中国石油化工股份有限公司西南油气分公司采气二厂 四川南充 637400
  • 收稿日期:2019-09-04 修回日期:2019-12-09 出版日期:2019-12-25 发布日期:2020-04-24
  • 通讯作者: 赵少伟,男,1984年11月生,2007年获中国石油大学(北京)学士学位,2010年获中国石油大学(北京)硕士学位,现为中海石油(中国)有限公司天津分公司高级工程师,主要从事海上油气田钻完井工程技术及管理工作。Email:zhaoshw@cnooc.com.cn
  • 作者简介:赵少伟,男,1984年11月生,2007年获中国石油大学(北京)学士学位,2010年获中国石油大学(北京)硕士学位,现为中海石油(中国)有限公司天津分公司高级工程师,主要从事海上油气田钻完井工程技术及管理工作。Email:zhaoshw@cnooc.com.cn
  • 基金资助:

    国家科技重大专项"渤海油田高效开发示范工程"(2016ZX05058)资助。

Fracture mode of unconsolidated sandstone based on elastic-plastic with linear strain-hardening

Zhao Shaowei1, Ma Yingwen1, Liu Feihang2, Li Haitao2, Zhang Jianfeng3   

  1. 1. Tianjin Branch, CNOOC China Limited, Tianjin 300450, China;
    2. State Key Laboratory of Oil and Gas Reservoir Geology and Development Engineering, Southwest Petroleum University, Sichuan Chengdu 610500, China;
    3. The Second Gas Production Plant, Sinopec Northweast Oil and Gas Company, Sichuan Nanchong 637400, China
  • Received:2019-09-04 Revised:2019-12-09 Online:2019-12-25 Published:2020-04-24

摘要:

渤海油区疏松砂岩储层埋深较浅,地层天然压实作用较弱,在压裂充填过程中表现出明显的非线性塑性特征,分析和研究疏松砂岩地层压裂过程的破裂模式对于破裂压力的预测和压裂充填施工设计具有重要的实际意义。基于线性强化弹塑性岩石本构力学模型,考虑压裂液渗滤效应,建立了疏松砂岩地层弹性和塑性双区井周应力模型,通过理论分析验证了应力模型的正确性。基于岩石的拉伸破坏和剪切破坏准则,获得了疏松砂岩压裂充填过程中井壁破裂压力预测模型和4种破裂模式,并利用现场数据验证了模型的可靠性。研究结果表明:井壁屈服后塑性区呈椭圆型,且长轴在最大主应力方向;塑性模量系数越大,塑性半径越小,破裂压力越小;屈服应力越大,塑性半径越小,破裂模式由塑性拉伸破坏、塑性剪切破坏向弹性拉伸破坏变化;随内摩擦角和内聚力逐渐增加,破裂压力增加到一定值后不再变化,破裂模式由塑性剪切向塑性拉伸变化。在渤海油区常规疏松砂岩物性范围内,破裂模式主要为塑性剪切破坏。

关键词: 疏松砂岩, 压裂充填, 线性强化弹塑性, 破裂压力, 破裂模式

Abstract:

Unconsolidated sandstone reservoirs in Bohai oil region are characterized by shallow burial depths, weak natural compaction, showing obvious non-linear plastic characteristics during frac packing. Analysis and study of the fracture mode for the fracturing process of unconsolidated sandstone strata has important practical significance for prediction of fracture pressure and construction design of frac packing. Based on the constitutive mechanical model of rock for elastic-plastic with linear strain-hardening, this study establishes a stress model around wells in unconsolidated sandstone strata in elastic and plastic zones while considering the percolation threshold effect of fracturing fluid and verifies the correctness of the stress model by theoretical analysis. Based on the tensile failure and shear failure criteria of the rock, the prediction model of the fracture pressure of sidewall and 4 kinds of fracture modes in the frac packing process of unconsolidated sandstones were obtained, and the reliability of the model was verified using field data. The results show that the plastic zone was elliptical at the post-yield sidewall, and the long axis is in the direction of the maximum principal stress; the larger the coefficient of plastic modulus, the smaller the plastic radius, and the smaller the fracture pressure; the larger the yield stress, the smaller the plastic radius. The fracture mode changes from plastic tensile failure, plastic shear failure to elastic tensile failure; as the internal friction angle and cohesion gradually increase, the fracture pressure does not change after increasing to a certain value, and the fracture mode changes from plastic shear to plastic tensile. In terms of the physical properties of conventional unconsolidated sandstone in Bohai oil region, fracture mode is mainly shown as plastic shear failure.

Key words: unconsolidated sandstone, frac packing, elastic-plastic with linear strain-hardening, fracture pressure, fracture mode

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