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    共和盆地干热岩GR2井现今地应力特征及断层稳定性分析

    In-situ stress characteristics and fault stability analysis of hot dry rock GR2 well in Gonghe Basin

    • 摘要:
      研究目的 地应力大小和方向是干热岩开发中井位部署、压裂设计和储层评价等方面的重要基础数据,研究储层应力状态对干热岩开发具有重要意义。
      研究方法 文章根据区域地质构造演化、震源机制解反演结果、节理裂隙统计、原地应力实测数据分析了共和盆地区域应力场的特征,结合共和GR2地热井储层构造、地层岩性特点建立三维模型,利用正交各向异性弹性本构关系,通过数值模拟获取了共和盆地GR2井的三维地应力数据,探讨了区域构造应力场及干热岩注水开发与断层稳定性。
      研究结果 结果表明:①模拟所得地应力分布与理论值吻合,满足初始位移精度要求,最终预估了井中地应力场分布特征;②在500~4500 m深度范围内,三向主应力总体表现为σv> σH >σh,表明该区域应力结构有利于正断层活动;③青海共和盆地最大水平主应力方向整体上呈北东(NE)向挤压变形作用为主,有利于花岗岩岩体具有低的流体渗透率、低的热流传导。④在统一的区域地应力场作用下, 研究区3900~4500 m干热岩注水开发过程中,当地面持续注入压力达到或超过约19.9 MPa 时,可能引起场区内断层的滑动失稳,导致中小地震的发生,在干热岩开发利用中需注意防范。
      结论 研究结果对共和盆地地球动力学研究及干热岩安全开发利用具有一定参考价值。

       

      Abstract:
      Objectives The magnitude and direction of in−situ stress are important parameters for well placement, fracturing design and reservoir evaluation in hot dry rock development. It is of great significance to study reservoir stress state for hot dry rock development.
      Methods In this paper, the characteristics of current stress field in Gonghe Basin are analyzed based on regional geological structure evolution, focal mechanism solution and inversion results, statistics of joints and fissures, and in−situ stress measured data. Combined with the reservoir structure and stratigraphic lithofacies characteristics of Gonghe GR2 well, a three−dimensional model is established, and the three−dimensional in−situ stress data of well GR2 in Gonghe Basin is obtained through numerical simulation by using orthogonal anisotropic elastic constitutive relation. The regional tectonic stress field and occurrence conditions of dry hot rock resources are discussed.
      Results The results show that: ① The simulated stress distribution is consistent with the theoretical value, which meets the requirements of initial displacement accuracy, and finally predicts the distribution characteristics of in−situ stress field in the well. ② In the depth range of 500~4500 m, the relationship of three principal stresses is principal stress is σv> σH h, indicating that the stress structure in this region is favorable to normal fault activity. ③ The maximum horizontal principal stress direction of Gonghe Basin in Qinghai province is mainly NE direction compression deformation, which is conducive to low fluid permeability and low heat transfer of granite. ④Under the action of a unified regional stress field, the faults may be come instability near the injecting well, when the continuous injection pressure on the ground reaches or exceeds about 19.9 MPa during the water injection development of 3900~4500 m depth in the study area, leading to the occurrence of medium and small earthquakes, which should be prevented in the development and utilization of the hot dry rock.
      Conclusions This study have certain reference value for geodynamics research and the safe development and utilization of dry hot rock in Gonghe Basin.

       

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