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| 各向异性地层井壁破裂压力预测 |
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马天寿1,2,唐弢1,陈平1,陈春宇3,孙少林4,刘阳1
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(1.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;2. 中国科学院武汉岩土力学研究所岩土力学与工程国家重点实验室,湖北武汉 430071;3.中国石油长庆油田公司油气工艺研究院,陕西西安 710018;4.中国石油西部钻探克拉玛依钻井公司,新疆克拉玛依 834009)
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| 摘要: |
| 地层破裂压力对于钻井和水力压裂非常重要,但直井破裂压力预测往往忽略了地层各向异性的影响。考虑岩石各向异性影响,推导直井井壁应力分布模型,建立各向异性地层破裂压力计算方法,并分析层理产状、各向异性程度、地应力及孔隙压力的影响。结果表明:低角度层理对破裂压力几乎无影响,而高角度层理对破裂压力影响显著;向最大水平地应力方向倾斜的层理,其破裂压力最低,极端情况下甚至比各向同性地层低50％,对井壁稳定极为不利;岩石各向异性程度越高,对破裂压力的影响越大;随着水平地应力比值和孔隙压力的增加,破裂压力整体上逐渐减小,而且地应力影响明显高于岩石各向异性,水平地应力比值增加后,岩石各向异性的影响进一步加剧;该模型提高了破裂压力计算的精度。 |
| 关键词: 岩石力学 各向异性 横观各向同性 井壁应力 破裂压力 |
| DOI：10.3969/j.issn.1673-5005.2019.03.009 |
| 分类号::TE 21 |
| 文献标识码:A |
| 基金项目:国家自然科学基金项目(41874216,0);四川省科技计划项目(2017HH0061) |
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| Prediction of fracture pressure of wellbore for anisotropic formations |
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MA Tianshou1,2, TANG Tao1, CHEN Ping1, CHEN Chunyu3, SUN Shaolin4, LIU Yang1
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(1.State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China;2.State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics,Chinese Academy of Sciences, Wuhan 430071, China;3.Oil and Gas Technology Institute of Changqing Oilfield Company, PetroChina, Xi 'an 710018, China;4.Karamay Drilling Company, PetroChina West Drilling, Karamay 834009, China)
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| Abstract: |
| The fracture pressure of wellbore is very important for drilling and hydraulic fracturing, while the influence of rock anisotropy has been ignored in the prediction of the fracture pressure. In this study, a stress distribution model around a vertical borehole considering the influence of rock anisotropy was deduced, and a computing method was proposed. The influence of the occurrence of bedding planes, the degree of anisotropy, the in-situ stress and pore pressure on the fracture pressure was analyzed. The results indicated that the bedding plane with a small dip angle almost has little influence on the fracture pressure, while the bedding plane with a large dip angle has a significant influence. When the azimuth of the bedding plane is along with the maximum horizontal in-situ stress, the fracture pressure will reach to its lowest value, and it even can be 50％ lower than that of an isotropic case, consequently, it is vulnerable to the stability of the borehole. The higher the degree of rock anisotropy, the greater impact on the fracture pressure. In general, the fracture pressure decreases with the increasing of the ratio of horizontal stresses and pore pressure. The influence of the in-situ stress on the fracture pressure is obviously higher than that of the rock anisotropy, while the effect of the anisotropy can be larger when the ratio of the horizontal stresses is high. The present model improved the computational accuracy of the fracture pressure, and it also can provide theoretical guides for drilling and hydraulic fracturing in anisotropic formations. |
| Key words: rock mechanics anisotropy transverse isotropy wellbore stress fracture pressure |
