致密油藏多级压裂水平井同井缝间注采可行性

以大庆油田L致密油藏为例,评价了L致密油藏的压裂改造效果;通过现代产量递减分析和试井分析,总结了生产动态规律;论证了水平井准天然能量、注水吞吐、注CO_2吞吐开发效果。针对致密油藏水平井产量递减快的问题,提出多级压裂水平井同井缝间注采方法,即通过注采分隔装置和注采阀进行同井缝间注采,将井间驱替问题转化为缝间驱替问题。采用数值模拟方法,分别计算了准天然能量衰竭开发、注水吞吐、CO_2吞吐、同井缝间注采4种方式的开发指标。分析结果表明,注水吞吐只能短期内提高累积采油量,不能显著提高采收率;同井缝间注采的产量比CO_2吞吐的产量高、稳产期更长、递减率更小、开发效果更好。进一步提出了致密油藏有效开发方式,即先以准天然能量衰竭式开采,控制地层压力均衡下降,在井底压力降到饱和压力附近时,转入同井缝间异步注采。现场实施时,采用水平井缝间强凝胶封堵完井工艺,即在注采缝之间的水平段射孔、注入强凝胶、封堵套管外侧与岩石连通空间。安装注采分隔装置和配注阀,采用温和注水方式,发挥裂缝的渗吸作用,能控制注入水的快速推进,提高致密油藏产量和采收率。

Feasibility of inter-fracture injection and production for the same multistage fractured horizontal well in tight oil reservoir

Taking the tight oil reservoir L in Daqing oilfield as an example, the effect of fracturing, modern production decline and bottom-hole pressure were analyzed, and the efficiency of quasi nature energy development, water swallowing-spitting, and CO₂ huff and puff were comprehensively evaluated. Aiming at the challenges in fast decreasing production of horizontal well in tight oil reservoir, the inter-fracture injection and production method in the same well for multistage fractured horizontal well was proposed, i.e., the injection and production separating device and valve were used for inter-fracture injection and production in the same well to transform the inter-well displacement into inter-fracture displacement. The numerical simulation method was adopted to calculate the development indexes of four patterns including quasi-nature-energy depletion development, water swallowing-spitting, CO₂ huff and puff and inter-fracture injection and production in the same well, respectively. The comparative analysis on the indexes of four development patterns shows that water swallowing-spitting can only improve cumulative oil recovery in a short term, unable to significantly improve oil recovery efficiency. The oil rate of inter-fracture injection and production in the same well is higher than that of CO₂ huff and puff, characterized by longer stable production period, smaller decline rate and better development effect. Meanwhile, the effective development method of tight oil reservoir was put forward, i.e., the quasi-natural-energy depletion development was firstly used to control the reservoir pressure with equilibrium decrease, and when the bottom-hole pressure was decreased to saturation pressure or so, it was transformed into inter-fracture asynchronous injection and production. During field implementation, the completion technology of inter-fracture strong-gel plugging for horizontal well was adopted, i.e., the strong gel was injected to interval perforation between the injection and production fractures for plugging the connected space between outer casing and rocks. Meanwhile, the injection and production separating device and valves were allocated and moderate water injection were used to play the imbibition function of fractures and control the rapid advancement of injected water, so as to improve the production and recovery efficiency of tight oil reservoirs.