应力敏感对裂缝性油藏合理注水时机及压力保持的影响

Effects of stress sensitivity on reasonable water-flooding time and pressure level in fractured reservoir

对于具有应力敏感的裂缝性油藏,在开发过程中因地层压力下降导致基质与裂缝体积缩小,渗流能力降低。如何有效抑制这种油藏特性对开发效果和最终采收率的影响,是制定裂缝性油藏开发策略的关键。本文以渤海某裂缝性油藏为例,对应力敏感与注水时机及地层压力保持水平之间的密切关系进行分析和研究。结果表明:在不考虑应力敏感时,裂缝性油藏合理注水时机为地层压力降至饱和压力时实施注水;在考虑应力敏感时,裂缝性油藏合理注水时机由应力敏感程度决定。当油藏压力降至饱和压力处渗透率保留率在80%以上时,注水时机为地层压力降至饱和压力时实施注水。否则,必须在原始地层压力实施注水。同时,裂缝性油藏合理地层压力保持水平应该维持合理注水时机下的地层压力不变,但考虑到后期提液、打井等挖潜措施及综合调整的实施,可根据实际情况适当提高。

For stress- sensitive fractured reservoirs,the decrease of seepage ability is inevitable due to reduction of pore volume caused by formation pressure drop in the process of development. How to effectively restrain the influence of it on the development effectiveness and ultimate recovery is the key to developing fractured reservoir development strategies. This paper takes a fractured reservoir in Bohai Oilfield as an example to study the effects of stress sensitivity on reasonable water-flooding time and formation pressure level. The results show that without consideration of stress sensitivity,the reasonable water- flooding time was when the formation pressure dropped to saturation pressure,while with consideration of stress sensitivity,it was determined by the degree of stress sensitivity. When the retention rate of permeability was above 80% at reservoir saturation pressure,the reasonable waterflooding time was also when the formation pressure dropped to saturation pressure. Otherwise,water-flooding must be carried out at original reservoir pressure. Meanwhile,the formation pressure for reasonable water-flooding time should be kept constant,or slightly elevated with consideration of subsequent developing measures and comprehensive adjustment.