基于低场核磁共振技术的致密砂岩气藏防水锁作用机理研究

致密砂岩气藏孔隙度、渗透率较低，微观孔喉尺度细小，在生产及压裂过程中极易产生水锁伤害。为开展致密储层防水锁作用机理研究，本文将常规岩心自吸实验、防水锁剂抑制水锁伤害实验与低场核磁共振技术相结合，从微观角度揭示致密砂岩储层微纳米级孔喉中的防水锁作用机理，为致密砂岩气藏防水锁相关研究提供理论依据。研究结果显示，加入防水锁添加剂后，流体表面张力下降，接触角增大，自吸速率变慢，渗透率有一定程度恢复；在此基础上，通过核磁共振T2谱从微观角度评价缓慢自吸阶段液体在不同孔喉尺度范围内的液相水锁滞留现象，其中加入防水锁添加剂后在自吸20h时在较小孔喉处自吸液相平均占比为38.61%，整体孔喉平均液相占比为35.79%。而在未加入防水锁试剂的样品中在自吸20h时在较小孔喉处液相占比为67.48%，整体孔喉占比为54.52%；通过防水锁剂抑制水锁伤害实验得出，加入防水锁剂后渗透率恢复程度在15.38%～20.19%，整体液相滞留占比平均下降幅度在10.73%。研究发现防水锁剂有效地降低了较小孔候处液相滞留占比，降低流体表面张力以及增大岩心疏水性能，揭示了致密砂岩气藏防水锁作用机理，为致密砂岩气藏降低水锁伤害程度、提高返排效率，为实现高效开发提供理论支撑。

Study on the mechanism of waterproof locking in tight sandstone gas reservoir based on low field nuclear magnetic resonance technology

Tight sandstone gas reservoirs have low porosity and permeability, and their micro pore throat size is small, making them prone to water lock damage during production and fracturing processes. In order to conduct research on the mechanism of waterproof locking in tight reservoirs, this article combines conventional core self suction experiments, waterproof locking agent inhibition of water locking damage experiments, and low-field nuclear magnetic resonance technology to reveal the waterproof locking mechanism in micro and nano pore throats of tight sandstone reservoirs from a microscopic perspective, providing a theoretical basis for research on waterproof locking in dense sandstone gas reservoirs. The research results show that after adding waterproof lock additives, the surface tension of the fluid decreases, the contact angle increases, the self suction rate slows down, and the permeability recovers to a certain extent; On this basis, the liquid phase water lock retention phenomenon of the slowly self absorbing phase liquid at different pore throat scales was evaluated from a microscopic perspective through nuclear magnetic resonance T2 spectroscopy. After adding waterproof lock additives, the average proportion of the self absorbing liquid phase at the smaller pore throat after 20 hours of self absorption was 38.61%, and the overall average proportion of the liquid phase at the pore throat was 35.79%. In the sample without the addition of waterproof lock reagent, the liquid phase proportion at the smaller pore throat was 67.48%, and the overall pore throat proportion was 54.52% after 20 hours of self absorption; Through the experiment of inhibiting water lock damage with waterproof locking agent, it was found that the recovery degree of permeability after adding waterproof locking agent ranged from 15.38% to 20.19%, and the average decrease in the proportion of overall liquid phase retention was 10.73%. Research has found that waterproof locking agents effectively reduce the proportion of liquid phase retention in smaller pores, reduce fluid surface tension, and increase core hydrophobicity. This reveals the mechanism of waterproof locking in tight sandstone gas reservoirs, providing theoretical support for reducing water lock damage and improving flowback efficiency in tight sandstone gas reservoirs, and achieving efficient development.