南海天然气水合物试采储层热流耦合与温度场调控研究进展

Research progress on thermal-fluid coupling and temperature field regulation in natural gas hydrate production tests in the South China Sea

中国南海天然气水合物储层类型以泥质粉砂为主,与其他国家和地区的砂质储层相比开采难度大。本文针对南海北部泥质粉砂天然气水合物降压开采涉及的相变习性演化、有效渗透率变化、热流耦合模式、试采系统温度场调控与矿场尺度增温防冰等关键问题,综述了笔者团队近年来取得的最新研究成果。研究表明,泥质粉砂型水合物相变始终处于动态平衡状态,储层因富含黏土水合物相变滞后效应明显;试采井壁处节流膨胀效应强烈,“温度漏斗”斜率最大,一旦形成“水锁”与生成二次水合物,气相渗流能力将明显降低;在无外部热源补给情况下,较高的产气速率,易造成水合物分解速率减缓直至停止分解,中国南海泥质粉砂水合物分解主要受传热控制模式影响,亟需建立有效的“储层-井筒”试采系统多元温压调控与安全流动机制,提高产气效率;依托自然资源部青海木里天然气水合物与冻土环境野外科学观测研究站,利用原位补热降压充填的水合物开采方法,成功完成矿场尺度水合物试采系统温度场改造试验,进一步优化提高了储层渗流能力,实现了增渗扩产目的。

Gas hydrate reservoirs in the South China Sea are mainly composed of clayey silts,presenting exploitation challenges compared to sandy reservoirs.This paper summarizes recent research by our team,focusing on the evolution of phase change behaviors,effective permeability changes,heat flux coupling mode,temperature field regulation within the trial production system,and mine-scale warming and antiicing involved in the depressurization mining of clayey silt gas hydrates in the northern South China Sea.The results show that the phase transitions in clayey silt hydrate are consistently in dynamic equilibrium,exhibiting a pronounced hysteresis effect due to the high clay content.The throttling expansion effect is strong at the test production wall,resulting in the steepest“temperature funnel”slope.Once a“water lock”forms and secondary hydrate generation occurs,gas-phase seepage capacity significantly decreases.In the absence of external heat source recharge,high initial gas production rates can hinder hydrate decomposition,potentially leading to cessation of decomposition.The decomposition of clayey silt gas hydrates in the South China Sea is mainly affected by heat transfer control mode.Therefore,developing an efficient“reservoir-wellbore”trial production system with multiple temperature and pressure regulation methods and robust flow mechanisms is crucial to improving gas production efficiency.Relying on the Qinghai multi-natural gas hydrate and permafrost environment field scientific observation and research station of the Ministry of Natural Resources,the in-situ heating and pressure reduction filling method was used to successfully complete the temperature field transformation test of a mine-scale hydrate trial production system.This further optimized and improved the seepage capacity of the reservoir and realized the purpose of increasing permeability and expanding production.