基于ANSYS的断层安全性评价方法及应用--以苏北盆地东台坳陷白驹含水层储气库为例

Evaluation method for fault safety and its application based on ANSYS:a case study of Baiju aquifer gas storage in Dongtai Depression,Subei Basin

含水层储气库利用多孔介质储层储蓄天然气,选址的地理范围较广,不依赖于大型盐矿或者衰竭油气藏,对我国天然气战略具有重大意义。含水层储气库通过天然断层封堵天然气、固井技术实现周期性注采,达到调节季节性峰值的目的,受注采压力变化的影响,运行过程断层容易开启或破裂,导致天然气泄漏。因此,含水层储气库断层安全性评价至关重要,而常见的断层评价和数值模拟方法没有涉及到多孔介质储层,对其膨胀机理研究尚浅,不适合用于含水构造的断层安全性评价。基于含水层储气库的基本特征,借助ANSYS有限元模拟和静态力学分析总结出一套完整的断层安全性评价方法。以苏北盆地东台坳陷大丰—兴化探区白驹储气地质体为例,构建出地层—断层的3D实体模型,根据初始应力平衡分析和断层岩石样本的轴压实验论证模型的有效性,通过位移约束法模拟不同运行压力条件下目标断层的应力状态,预测运行压力的极限值为29.50 MPa,超过该值断层可能发生拉张破坏。

Aquifer gas storage uses porous media reservoir to store natural gas.The location of aquifer gas storage has a wide geographical range and does not depend on large salt mines or depleted oil and gas reservoirs,which is of great significance to China’s natural gas strategy.Aquifer gas storage realizes periodic injection-production through natural fault blocking natural gas and cementing technology,so as to achieve the purpose of adjusting seasonal peak value.Affected by the change of injection-production pressure,faults are easy to be opened or broken during operation,leading to the leakage of natural gas stored.Therefore,it is very important to evaluate the fault safety of aquifer gas storage,but the common fault evaluation and numerical simulation methods do not involve the porous media reservoir,and the study of its expansion mechanism is insufficient,which does not satisfy the fault safety evaluation of water⁃bearing structure.Based on the basic characteristics of aquifer gas storage,this paper summarizes a set of complete fault safety evaluation methods by ANSYS finite element simulation and static mechanics analysis.A case study was carried out in Baiju aquifer gas storage in the Dongtai Depression of the Subei Basin.A 3D entity model of formation and fault was established.According to the initial stress equilibrium analysis and the axial compression experiments of fault rock samples,the validity of the model can be demonstrated.With displace⁃ment constraint method,the stress state of target faults at different operating pressure was simulated.The maximum value of predicted operating pressure is 29.50 MPa,and tensile failure may occur above this value.