鄂尔多斯盆地致密油应力循环压裂技术

鄂尔多斯盆地长7致密油Ⅱ类储层脆性指数低、水平两向应力差较大、天然裂缝不发育，常规混合水压裂难以形成复杂裂缝，单井产量低，为此研发了应力循环压裂技术。通过物模实验明确了该压裂技术增产机理，完成了工艺优化和工具配套。该工艺采用应力循环压裂工具泵注高砂浓度液体，在环空注入净液体，根据压裂过程中地层响应和压力变化，实时控制井底砂浓度和排量，对储层加载循环应力，使储层受到疲劳破坏，实现缝网压裂。现场试验37口井，平均施工规模与常规混合水压裂相当，施工排量仅为常规混合水压裂的一半即可实现多次缝内升压，较对比井有效改造体积增加44.5%，单井日产油量提高1.6 t。

Stress-cycle fracturing technology suitable for tight oil reservoirs in the Ordos Basin

Type Ⅱ reservoirs of Chang 7 tight oil reservoir in the Ordos Basin are characterized by low brittleness index, larger horizontal bidirectional stress difference and undeveloped natural fractures, so complex fractures can be hardly created by means of conventional mixed water fracturing and the single-well production rate is low. To deal with this situation, a stress-cycle fracturing technology was developed. In this paper, its stimulation mechanisms were clarified by means of physical stimulation experiments, and the technological optimization and tool matching were completed. In this process, the liquid of high proppant concentration is pumped by using the stress-cycle fracturing tool, and the net liquid is injected into the annulus. The proppant concentration and displacement at the bottom hole is controlled in real time according to the formation response and pressure change in the process of fracturing. Cyclic stress is applied to the reservoir so that the reservoir is suffered from the fatigue failure and fracture network is formed. The stress-cycle fracturing technology was test on site in 37 wells. Its average construction size is equivalent to that of conventional mixed water fracturing, but its construction displacement is only half of the conventional mixed water fracturing when inter-fracture pressure increasing has been realized many times. And compared with the reference well, the effective stimulated reservoir volume is increased by 44.5% and the single-well daily oil production is increased by 1.6 t.