Bui Dung, Nguyen Tan, Nguyen Thanh, Yoo Hyunsang
New Mexico Tech, Socorro, New Mexico USA.
Computer Modelling Group, Calgary, Canada.
J Pet Explor Prod Technol. 2023;13(1):163-184. doi: 10.1007/s13202-022-01544-8. Epub 2022 Jul 19.
Formation damage in drilling comes from drilling fluid invasion due to high differential pressure between a wellbore and the formation. This mechanism happens with fracture fluid invasion of multi-fractured horizontal wells in tight formations. Some multi-fractured wells show production rates and cumulative productions far lower than expected. Those damaged wells may sustain further impact such as well shutting due to unexpected events such as the COVID-19 outbreak and then experience a further reduction in cumulative production. This paper focuses on the root causes of formation damage of fractured wells and provides possible solutions to improve production. A simulation study was conducted using Computer Modelling Group software to simulate formation damage due to fracture fluid invasion and well shut-in. Simulation results revealed that the decrease in cumulative hydrocarbon production due to leak-off and shut-in of the simulated well could range from 20 to 41%, depending on different conditions. The results showed that the main causes are high critical water saturation of tight formations, low drawdown, and low residual proppant permeability under formation closure stress. The sensitivity analysis suggests two feasible solutions to mitigate formation damage: optimizing drawdown during production and optimized proppant pack permeability of the hydraulic fracturing process. Optimizing pressure drawdown is effective in fixing leak-off damage, but it does not mitigate shut-in damage. Formation damage due to shut-in should be prevented in advance by using an appropriate proppant permeability. These key findings enhance productivity and improve the economics of tight gas and shale oil formations.
钻井过程中的地层损害源于井筒与地层之间的高压差导致的钻井液侵入。这种机制在致密地层中的多段压裂水平井的压裂液侵入时也会发生。一些多段压裂井的产量和累计产量远低于预期。那些受损的井可能会受到进一步的影响，例如由于新冠疫情爆发等意外事件导致的井关闭，进而使累计产量进一步下降。本文聚焦于压裂井地层损害的根本原因，并提供提高产量的可能解决方案。使用计算机模拟集团软件进行了一项模拟研究，以模拟压裂液侵入和关井导致的地层损害。模拟结果表明，根据不同条件，模拟井由于滤失和关井导致的累计烃产量下降幅度可能在20%至41%之间。结果表明，主要原因是致密地层的临界水饱和度高、生产压差低以及在地层闭合应力下支撑剂残余渗透率低。敏感性分析提出了两种减轻地层损害的可行解决方案：生产过程中优化生产压差以及水力压裂过程中优化支撑剂充填渗透率。优化生产压差对修复滤失损害有效，但不能减轻关井损害。应通过使用合适的支撑剂渗透率提前预防关井导致的地层损害。这些关键发现提高了致密气和页岩油地层的产能并改善了经济效益。
