Abstract:

Well shut-in after fracturing is of great importance for increasing the oil recovery and production of shale oil reservoirs. The key is to determine the shut-in time. At present，there is no systematic and effective method for determining the time of shut-in either in China or across the world. The pressure transmission of the fracture system，the ion diffusion of the produced fluid and the capillary force imbibition are the key problems to be solved for addressing the above challenges. With laboratory experiments and field analysis，a comprehensive determination method for the shut-in time for Jimsar shale oil reservoirs was developed by clarifying the microscopic pore characteristics，wettability，laminae，and imbibition flooding potential of Jimsar shale oil reservoirs and analyzing the existing methods used and characteristics of shut-in time determination. It is concluded that the Jimusar shale oil reservoir provides strong imbibition and diffusion ability，and well shut-in after fracturing contributes to the displacement of oil. The shut-in time can be determined comprehensively in accordance with the required equilibrium time of the wellhead pressure，imbibition，and production fluid salinity. To determine the post-fracturing shut-in time for Jimsar shale oil reservoirs，the synergy of micro-fracture fluid charging and matrix imbibition should be taken into consideration. Specifically，with the second turning point of wellhead pressure decline taken as the lower limit and the turning point for the stable rising of salinity as the upper limit，the optimal shut-in time is determined，considering the imbibition equilibrium. The shut-in time after fracturing for Well Q was optimized based on laboratory experiments and field data. The suggested shut-in time for Well Q is about 55 days. This study provides an important reference for optimizing the shut-in time after fracturing.

Key words:

"> Jimsar shale oil, fracturing development, well shut-in after fracturing, shut-in time, laboratory experiment, field analysis

摘要： 压后闷井对提高页岩油储层的采收率及产量具有重要意义，闷井时间的确定尤为关键。目前，闷井时间的确定在国内外仍未形成系统、有效的方法。裂缝系统压力传递、产出液离子扩散、毛管力渗吸是解决上述难点的关键科学问题。以室内实验和现场分析为主，在明确吉木萨尔页岩油储层微观孔隙特征、润湿性、纹层、以及渗吸驱油潜力的基础上，分析了现有闷井时间确定方法及特点，形成了吉木萨尔页岩油储层闷井时间综合确定方法。研究得出：吉木萨尔页岩油储层具有较强的渗吸扩散能力，压后闷井对原油产出起到驱替作用。闷井时间由井口压降平衡时间、渗吸平衡时间、产出液矿化度平衡时间综合确定。吉木萨尔页岩油储层压后闷井需要考虑微裂缝充液和基质渗吸协同作用，以井口压降第二转折点为下限、矿化度演化稳定上升转折点为上限、结合渗吸平衡得到最优闷井时间。基于室内实验和现场数据对Q井压后闷井时间进行了优化，推荐Q井闷井时间为55 d左右。该研究为优化吉木萨尔页岩油压后闷井时间提供了重要依据。

关键词:

吉木萨尔页岩油, 压裂开发, 压后闷井, 闷井时间, 室内实验, 现场分析