低/特低渗透油藏砂–泥岩复合岩性模型吸水特征研究

Water Absorption Characteristics of Sand-Mudstone Composite Lithology Model in Low/Ultra Permeability Reservoirs

摘要: 大庆朝阳沟油田低/特低渗透油藏自1986年以来历经30多年水驱开发，目前已进入中高含水阶段，地下油水分布状况复杂，呈现出高注采比、低地层压力保持水平的现象，与常规油藏符合物质平衡理论的现象具有较大差异。本文以朝阳沟油田为研究对象，研制符合低/特低渗透油藏地质特征的砂–泥岩复合岩性模型，开展储层、过渡岩性、泥岩等不同岩性的吸水特征实验，分析油水分布状况，深入研究低/特低渗透油藏注水开发普遍高注采比的原因。研究结果表明，除了砂岩储层吸水外，过渡岩性、含砂泥岩、纯泥岩均有不同程度的吸水能力，吸水量分别占30%、11%、7%，即仅有52%左右的注入水在地层条件下真正驱替原油，这一研究成果揭示了低/特低渗透油藏注水量高、地层压力低的真实原因，为低/特低渗透油藏砂–泥岩储层有效开发对策的制定提供了依据。

Abstract: Low/ultra-low permeability reservoirs in Chaoyanggou of Daqing Oilfield have been developed by water flooding for more than 30 years since 1986. At present, it has entered the stage of medium-high water cut, and the distribution of underground oil and water is complex, showing a phenomenon of high injection-production ratio and low formation pressure maintenance level, which is quite different from that of conventional reservoirs in conformity with material balance theory. Taking Chaoyanggou Oilfield as the research object, this paper develops a sand-mudstone composite lithology model which conforms to the geological characteristics of low/ultra-low permeability reservoirs, and carries out water absorption experiments of different lithologies such as reservoir, transitional lithology and mudstone. Then root cause of the difficulty of remaining water to effectively supplement formation energy under the condition of high injection-production ratio is deeply studied, and the distribution of oil and water by water flooding is determined. The results show that in addition to reservoir water absorption, transitional lithology, sandy mudstone and pure mud-stone have different water absorption capacity. Water absorption accounts for 30%, 11% and 7% respectively. That is to say, only about 52% of injected water can really play the role of water displacement of crude oil under formation conditions. This research finding reveals the real reason for high-amount water injection and low formation pressure in low/ultra-low permeability reservoirs, and provides a basis for formulating effective development countermeasures for sand-mudstone reservoirs in low/ultra-low permeability reservoirs.