鄂尔多斯盆地长7致密油水平井体积压裂开发效果评价及认识

鄂尔多斯盆地长7致密油水平井衰竭式开发产量递减变化规律可分为3个阶段:一是初期稳产阶段,主要受人工裂缝周围体积压裂未返排液补充能量的影响;二是递减较快阶段,由压裂未返排液能量补充向溶解气驱的转化过程;三是稳定递减阶段,主要受溶解气驱的控制,基本符合双曲递减规律。在这些基本规律认识的基础上,结合现场开发试验效果评价,确定合理的水平井体积压裂衰竭式开发关键技术参数:井距500~600 m,人工裂缝段间距90 m;排量10~12 m3/min,单段入地液量和加砂量分别约为1 100和100 m3;生产流压在初期稳产阶段略大于饱和压力,递减较快阶段略低于饱和压力,稳定递减阶段保持不低于饱和压力的2/3;致密油示范区水平井初期单井产量达到周围定向井的8~10倍;年累积产量达到同样面积直井的1.4~1.8倍,取得了较好的实施效果。

Assessment of fracturing treatment of horizontal wells using SRV technique for Chang-7 tight oil reservoir in Ordos Basin

A stimulated reservoir volume (SRV) technique was used in a tight oil reservoir (Chang-7) in Ordos Basin of China to increase oil production. The production process in a horizontal well with the SRV treatment was analyzed, and three stages can be characterized, including an initial stable production, a rapid decline period and a stable decline stage. The initial stable production is mainly influenced by the remaining fluids in the SRV that can supply energy for production. During the rapid decline period, the transfer of the energy-supplying from the SRV fluids to dissolved gas driving occurs. In the stable decline stage, oil production is mainly controlled by dissolved gas driving, which is basically conformed to a hyperbolic decline pattern. The SRV treatment and production parameters were optimized based on the data analysis of existing wells. It is suggested that the optimum horizontal well spacing is 500 to 600 m, and the interspace distance of hydraulic fracturing intervals is best of 90 m. The injection rate of the fracturing fluid can be set as 10 to 12 m³/min, with the total fluid volume of 1100 m³ during each treatment and with 100 m³ sands. The bottomhole flow pressure is better retained approximately greater than the bubble pressure in the initial stable stage, and can be slightly less than the bubble pressure in the rapid decline stage, while it should be not less than 2/3 of the bubble pressure in the stable decline stage. The initial production rate of the wells treated by the SRV technique is 8-10 times higher than that of the un-treated, and the annually cumulative production of the SRV treated horizontal wells is 1.4 to 1.8 times of those fractured vertical wells with the same coverage area.