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一种新的选择性堵塞方法用来改善体积波及效率,从而提高油田的采收率。此方法建立在“盐析”的理论基础上,即在水中加入某种非电解质,使水中的电解质溶解度下降。在这种新的段塞驱油过程中,先注入浓缩盐水预冲洗,然后注入一种或多种水溶性酒精(如乙醇)到油藏中。酒精和卤水的混合将引起盐析。由于酒精和浓缩卤水对水的高相渗透性使之易于进入水浸地带。固体的析出可部分或全部堵塞高渗透地带,导致后置液流进含油饱和度高的低渗透带。因此油藏的大部分就为这种流体所波及,油藏的体积波及效率和采收率将不言而喻地得到改观。在均质填砂模型流动试验中可以观测到渗透率可以下降到70%,在非均质填砂模型流动试验中,渗透率将下降到原卤水的50%。试验结果说明,该方法能够多采出15%的原始石油地层储量。与其它选择性渗透率降低的技术相比,此方法有许多优点。它可应用于深部或浅部油藏,另外,如果有必要的话,可通过低盐饱和度的卤水注入来恢复高渗透带的渗透率。
A new selective plugging method is used to improve volume sweep efficiency, thereby enhancing oil recovery. This method is based on the theory of “salting-out”, which involves adding some non-electrolyte to water and decreasing the solubility of electrolyte in water. In this new slug flooding process, a concentrated brine is injected first and then one or more water soluble alcohols, such as ethanol, are injected into the reservoir. The mixture of alcohol and brine will cause salting out. The high permeability of water to alcohol and concentrated brine makes it easy to enter the flooding zone. Precipitation of solids may partially or fully block the high permeability zone, causing the backfluid to flow into the low permeability zone with high oil saturation. As a result, most of the reservoir is affected by this fluid, and the volumetric efficiency and oil recovery of the reservoir will be self-evidently changed. It can be observed that the permeability can be reduced to 70% in the homogeneous sand flow model test. In the heterogeneous sand packing model, the permeability will drop to 50% of the original brine. The experimental results show that this method can recover more than 15% of the original oil formation reserves. This method has many advantages over other techniques with reduced selectivity. It can be applied to deep or shallow reservoirs and, if necessary, the permeation of high permeability strata can be restored by brine injection of low salt saturation.