富油煤是集煤、油、气属性于一体的煤炭资源,主要赋存于中低阶煤类中,具有高焦油产率的特点。富油煤的原位热解是将煤层不经开采直接于地下加热方式热解产出小分子油气的一种技术,从而达到高效、清洁利用富油煤资源的目的。为明确多因素在注气体原位热解传热过程中的影响规律,探索加热过程中制约热解效果的矛盾关系,通过Fluent数值模拟方法,构建了煤层、加热井及生产井为一体的三维模型,研究了加热介质、流体流速、流体温度、裂缝分布等因素对整体煤层温度场分布的影响规律。数值模拟结果表明:不同加热介质对煤层温度提升的效果差异不显著,与水蒸气和氮气相比,CO2作为加热介质的效果相对较好。在单一裂缝的加热条件下,采用不同流速,有效加热区域的占比难以提升至25%以上,煤层平均温度均低于380℃。提升加热介质的温度对整体升温速率提升较显著,每提升加热介质温度50℃,可提高有效加热区域8%,提升煤层平均温度29℃。在3条裂缝加热条件下,加热速率较单井模式下大幅提高,可在2a内将整个煤层温度提升至100%有效加热范围。多条横裂缝中的流体分布不均匀情况可通过添加纵裂缝的方式改善。通过探究不同因素对富油煤热解过程热能传导与利用的影响,强化富油煤加热过程中传热及提升热能利用效率。

Tar-rich coal is a kind of coal resource with the properties of coal, oil and gas, mainly occurring in middle and low rank coal,with the characteristics of high tar yield. In situ pyrolysis of tar-tich coal is a technology that produces small molecule oil and gas by un⁃derground heating without mining, thereby achieving efficient and clean utilization of tar-tich coal resources. In order to clarify the influ⁃ence rule of multiple factors in the heat transfer process of in-situ pyrolysis of gas injection and explore the contradictory relationship re⁃stricting the heating rate in the heating process, a three-dimension model of coal seam, heating well and production well was constructedby using Fluent numerical simulation method. The influence of factors such as heating medium, fluid velocity, fluid temperature and frac⁃ture distribution on the overall temperature field distribution of coal seam was studied. The numerical simulation results show that there isno significant difference in the effect of different heating media on the temperature of coal seam. Compared with water vapor andnitrogen, carbon dioxide as the heating medium has a relatively better effect. The proportion of effective heating zone cannot be increasedto more than 25% with different flow rates under the heating condition of a single fracture, and the average temperature of coal seam is alsolower than 380 ℃ . The overall heating rate can be increased significantly by increasing the temperature of heating medium.When increas⁃ing the temperature of the heating medium by 50 ℃ , the effective heating area can be increased by 8% fractures, and the average temper⁃ature of the coal seam is increased by 29 ℃ . Under the heating conditions of three cracks, the heating rate is greatly improved comparedwith that of single well mode, and the temperature of the entire coal seam can be raised to 100% effective heating range within 2 years.The uneven fluid distribution in multiple transverse fractures can be improved by adding longitudinal fractures. The influences of differentfactors on heat conduction and utilization in the pyrolysis process of tar-tich coal are obtained, which is conducive to the enhancement ofheat transfer and the improvement of heat utilization efficiency in the heating process of tar-tich coal.

0 引言

1 建模和方法

   1.1 几何模型

   1.2 网格系统及无关性验证

   1.3 物理模型与边界条件设置

   1.4 能量利用评价指标

2 结果与讨论

   2.1 加热介质种类对煤层温度场及传热规律的影响

   2.2 加热介质流速对煤层温度场及传热规律的影响

   2.3 流体温度对煤层温度场及传热规律的影响

   2.4 裂缝布置对加热效率及温度场均匀性的影响

3 结论