莺歌海盆地深层高含CO2高含水气藏气相渗流机理

南海莺歌海盆地深层气藏具有高温、高压、高含水和高含CO₂等典型特征,其渗流机理十分特殊。为揭示该类气藏渗流特征,剖析产气能力的影响因素,通过搭建超高温高压长岩心驱替实验系统来模拟实际储层的温压条件,开展不同含水条件及不同CO₂含量下的气相渗流实验。研究表明:该类气藏渗流特征可划分为产生启动压力、低速非达西渗流、达西渗流和偏离达西渗流4个阶段;束缚水会引起低速非达西渗流,可动水会导致启动压力产生,且束缚水在高压差下会转为可动水,导致气相渗流偏离达西渗流,形成或加剧气水两相流动,降低高压差下气相渗流能力;气组分中CO₂不仅会导致低速非达西渗流阶段时间延长,高含量下还会促进束缚水转为可动水,形成启动压力,并使高压差下偏离达西渗流阶段提前到来。因此,此类气藏含水饱和度和CO₂含量的增加均会抑制产气能力,应严格控制气藏生产压差,避免低速非达西渗流和高压差下偏离达西渗流产生。研究结果可为该类气藏的高效开发提供理论依据。

Gas Seepage Mechanism of Deep Gas Reservoirs with High CO2 and Water Content in Yinggehai Basin

The deep gas reservoirs in Yinggehai Basin, South China Sea is featured by typical characteristics such as high temperature, high pressure, high water content and high CO₂ content, resulting in a very special seepage mechanism. In order to disclose the seepage characteristics of these gas reservoirs and analyze the influencing factors of gas productivity, a experimental system of ultra-high-temperature and high-pressure long core displacement was established to simulate the temperature and pressure conditions of the actual reservoir, and gas seepage experiments were conducted with different water cuts and different CO₂ contents. It was found in the study that the seepage characteristics of the gas reservoir could be divided into four stages: initiation pressure, low-velocity non-Darcy seepage, Darcy seepage and deviation from Darcy seepage; bound water would cause low-velocity non-Darcy seepage, moving water might result in initiation pressure, and bound water would turn into moving water under high pressure difference, making gas seepage deviate from Darcy seepage, causing or aggravating gas-water flowing and reducing gas seepage at high pressure difference; CO₂ in the gas not only prolonged the low-velocity non-Darcy seepage, but also promoted the conversion of bound water into moving water at high content, forming initiation pressure and bringing forward the deviation from Darcy seepage at high pressure difference in advance. Therefore, the increase in water saturation and CO₂ content in these reservoirs will inhibit gas production, and production pressure differential should be strictly controlled to avoid low-velocity non-Darcy seepage and deviation from Darcy seepage at high pressure difference. The results of the study may provide a theoretical basis for the efficient development of these gas reservoirs.