工程扰动下煤层气储层井周煤岩力学行为与稳定性研究

Under the effect of drilling and reservoir fracturing, the surrounding coal of coalbed methane reservoir wellbore is cracked with low mechanical strength and complex geological environment, coalbed methane wellbore disasters expecially the instability of surrounding coal of wellbore occur frequentley, which seriously restrict the exploration of coalbed methane. In this project, the mechanicle characteristics of thermo-fluid-solid coupling of coal containing methane will be studied through the mechanical experiments of thermo-fluid-solid coupling. The deformation and failure rules of surrounding coal of coalbed methane reservoir wellbore will be investigated through model tests. According to the experimental results, based on the theories of rock mechanics, fracture mechanics and damage mechanics, a constitutive model for thermo-fluid-solid coupling of coal containing methane on the condition of temperature, stress and seepage gradient will be built. Furthermore, combining with the theory of non-linear science, such as mutation theory, fractal theory, fuzzy mathematic theory and artificial neural network, the instability mechanical condition of surrounding coal of coalbed methane reservoir wellbore will be obtained quantificationally. Moreover, the mechanical behavior and stability of surrounding coal of coalbed methane reservoir wellbore under the effect of drilling and reservoir fracturing will be analyzed with the numerical analysis software of COMSOL. Finally, the instability mechanism and failure criterion of surrounding coal of coalbed methane reservoir wellbore under the effect of drilling and reservoir fracturing will be put forward. The results will not only stimulate the emergence and development of the theoretical system of non-linear dynamics of instability disaster of surrounding coal of coalbed methane reservoir wellbore and accelerate the process of exploitation and development of coalbed methane, but also provide theoretical guidance for solving the wellbore stability problem in drilling conventional natural gas acrossed coal seam and coal mining in deep strata.

受钻进、储层压裂改造等工程扰动影响，煤层气储层井周煤岩破碎，结构强度显著降低，加之所处地质环境复杂，井工灾害尤其是失稳破坏时常发生，严重制约煤层气开发。本项目拟通过热流固耦合力学实验，研究含煤层气煤岩力学、强度特性；通过工程扰动下井周煤岩力学行为模型实验，研究煤层气储层井周煤岩失稳破坏机制与模式。基于岩石力学、断裂力学、损伤力学理论，建立含煤层气煤岩在温度、应力及渗流场下的热流固耦合本构模型；结合突变理论、分形理论、模糊数学及神经网络等非线性科学方法，定量推算井周煤岩失稳破坏的力学条件。并采用COMSOL数值软件，分析工程扰动下煤层气储层井周煤岩力学行为及稳定性。最终提出在工程扰动下井周煤岩破坏失稳机理与判据。研究成果不仅能促进煤层气储层井周煤岩失稳灾害非线性动力学理论体系的产生与发展、加快煤层气勘探开发进程，且可为有效解决常规天然气开采中穿越煤层的井壁稳定问题及深部煤炭开采提供理论指导。

受钻进、储层压裂改造等工程扰动影响，煤层气储层井周煤岩破碎，结构强度显著降低，加之所处地质环境复杂，井工灾害尤其是失稳破坏时常发生，严重制约煤层气开发。项目在煤层气储层煤岩物化特性与应力环境特征研究基础上，开展煤岩蠕变力学与热流固耦合力学特性研究、煤层气井钻进和围岩压裂物理模型试验与数值模拟、及煤岩强度准则与井眼坍塌预测方法研究。首先，基于欠平衡钻井随钻监测，建立气层识别和介质类型定性评价方法，提出随钻气层渗透率、孔隙度及饱和度评价模型。基于黄氏模型和弹性力学，建立构造应力地层地应力测井解释模型。结合室内试验与测井解释，得到煤层气储层物化与力学特性、地应力环境特征。其次，根据煤层气储层煤岩力学物性环境特征，开展煤岩蠕变与热流固耦合力学试验，揭示煤岩在应力、温度与渗流下的力学特性，构建改进煤岩西元蠕变模型和基于能量角度煤岩蠕变力学模型，及建立含气煤岩孔隙率与渗透率模型、变形控制方程、渗流场控制方程和温度场控制方程等热流固耦合力学模型。第三，通过含气煤岩的流固耦合力学试验，揭示煤层气渗流与恒压对煤岩力学强度特性的影响及其机理。第四，根据煤层气井底压力变化，开展不同卸围压程度含气煤岩力学试验，揭示煤岩在该过程中的力学行为特性与气体渗流特征，并得到考虑井底压力降低引起卸压效应的煤层气井眼坍塌压力变化规律。第五，通过煤层气储层钻进物理模型试验和数值模拟，揭示井周煤岩受温度、应力和气体渗流影响的应力分布、围岩变形与气体渗流特征。最后，根据煤岩破碎结构特征，构建弱面破坏强度准则，通过累加迭代法求解煤层坍塌压力，并编制煤层气井眼坍塌压力计算软件。项目研究成果不仅能促进煤层气储层井周煤岩失稳灾害力学理论体系的产生与发展、加快煤层气勘探开发进程，且可为有效解决常规天然气开采中穿越煤层的井壁稳定问题提供理论指导。同时，相关方法可为石油工程类似科学问题研究借鉴。