超低渗透油藏采油井投产前压裂时机优化研究

Fracturing time optimization of oil wells before put into production of ultra-low permeability reservoirs

通过室内实验研究表明，超低渗透油藏随着超前注水量的增加，油藏渗透率、微裂缝、启动压力梯度及油相相对渗透率发生明显的变化，以超低渗透油藏华庆油田长6储层为例，在储层特征研究及室内实验的基础上，利用渗流力学原理，确定了该储层的最小启动压力梯度和临界渗透率，其中，低于临界渗透率的储层压裂时机应该着重改善油水井间驱替关系，在水井投注初期对其进行压裂改造；对于渗透率高于临界渗透率的储层，合理的压裂时机应早于储层建立有效压力驱替系统时间，同时不超过水驱前缘到达裂缝半长时间。最终建立了有效压力驱替系统和油井见水时间图版。

Laboratory research showed that, with the increase of waterflooding in advance, the permeability, micro-cracks, starting pressure gradient, and oil relative permeability of the uhralow permeability reservoirs changed significantly. Taking uhralow permeability Chang6 reservoirs in Huaqing oilfield as an example, and using the theory of percolation mechanics, the minimum starting pressure gradient and the critical permeability of the reservoirs are detennined in the article, on the basis of research on the reservoir characteristics and laboratory experiments. Among them, the fracturing timing of the reservoirs with less than the critical permeability should focus on improving the oil-water relationship between the producers and injectors, conducting fracturing at the early stage of putting into production of the injectors. For reservoirs with more than the critical permeability, the reasonable fracturing timing should be earlier than the time at which the effective pressure displacement system was established in the reservoirs, meanwhile not exceeding the time at which the waterflooding front got to the half-length of the fracture. Plates of effective pressure displacement system and water breakthrough time of the injectors are established eventually.