储层扰动条件下煤系烃源岩的摩擦滑动特性

With global energy demand soaring and the climate-threat, (un)conventional gas (such as natural gas, coalbed methane, and shale gas) production forms a topic of intense ongoing interest in the energy sector. However, induced seismicity has become increasingly widespread in the Groningen gas field in Netherlands, and unconventional oil- and gas- producing areas in the United States and western Canada, as well as in the (un)conventional gas fields in China. These events are strongly correlated to anthropogenic behaviour of gas extraction, hydraulic fracturing and fluid injection, though the mechanisms still remain unclear. Understanding (un)conventional gas production-induced seismicity will be crucially important. Coal and coal-rich rock, as one of the main source rocks for (un)conventional gas formation, may play a role in fault slip (in)stability after reactivation and induced seismicity. In this project, we aim to investigate any effects of coal present on fault friction and slip (in)stability. To achieve this, we will perform dynamic friction experiments on simulated fault gouges prepared from coal and coal-rich rocks, collected from (un)conventional gas production areas in China. We will perform velocity stepping, constant velocity, slide-hold-slide (SHS), load-unload-load (LUL) friction experiments, under near in-situ reservoir conditions of 40-100℃, 10-50 MPa pore fluid pressure and 25-100 MPa confining pressure, employing sliding velocities of 0.1-100 µm/s. Data on the frictional strength and rate-dependence of friction will be obtained from these experiments, and a full Rate and State Friction (RSF) description will also be provided. Moreover, fault fabric evolution and the change in molecular structure of coal will be analyzed with the aid of SEM, Raman spectrometer and XRD. Finally, we will synthesize our results to elucidate the likely mechanisms responsible for the role of coal present in fault friction and (un)stable slip. The experimental data obtained will be delivered to the scientific community, and this research will also provide fundamental data that can contribute to understanding induced seismicity.

天然气、煤层气及页岩气等（非）常规天然气开采可能诱发地震。煤系烃源岩是（非）常规天然气的主要源岩，也是开采扰动岩层，其滑动稳定性将影响储库断层的稳定性。本项目拟通过摩擦实验、构造成分分析以及理论分析相结合的研究方法，揭示储层（埋深1-4km）条件下煤及含煤断层的摩擦滑动规律及控制机理。拟应用常规三轴仪开展在储层压力（25-100MPa）、孔隙压力（10-50MPa）及温度（40-100℃）条件下摩擦滑动实验研究，测量煤及含煤断层泥在不同滑动速率下的摩擦强度。应用速率-状态摩擦模型，揭示煤系烃源岩在不同实验条件下的速率依赖性。使用X-射线衍射、拉曼光谱仪及扫描电镜等方法分析摩擦滑动对样品构造、成分及剪切滑动带演化的作用。通过综合分析厘清煤对断层摩擦特性的影响。研究成果将揭示采气、注水等过程对含煤断层滑动稳定性的影响，为综合评价（非）常规天然气开采诱发地震提供实验数据和理论依据。

天然气、煤层气及页岩气等（非）常规天然气开采可能诱发地震。煤系烃源岩是（非）常规天然气的主要源岩，也是开采扰动岩层，其滑动稳定性将影响储库断层的稳定性。本项目通过摩擦实验、构造成分分析以及理论分析相结合的研究方法，揭示了储层（埋深1-4km）条件下煤及含煤断层的摩擦滑动规律及控制机理。应用常规三轴仪开展在储层压力（25-100MPa）、孔隙压力（10-50MPa）及温度（40-100℃）条件下摩擦滑动实验研究，测量了煤及含煤断层泥在不同滑动速率下的摩擦强度。结果表明当含煤量（体积分数）超过50%时，煤-页岩混合样品表现出显著滑动弱化行为，摩擦系数从峰值~0.5降低至稳态~0.3。微观机理分析显示其控制机理为断层R、B和Y剪切带的发育以及剪切形变促进的煤晶体结构发育共同作用。实验还发现（a-b）值明显受到孔隙流体成分、孔隙压和滑动速率的影响。滑动速率增加导致速率弱化行为向速率强化的转变，表明断层滑动稳定性从失稳转变为稳滑趋势。研究成果揭示了采气、注水等过程对含煤断层滑动稳定性的影响，为综合评价（非）常规天然气开采诱发地震提供了实验数据和理论依据。