四川盆地海相页岩气提高采收率研究进展与关键问题

Progress and key issues in the study of enhanced recovery of marine shale gas in Sichuan Basin

页岩气藏采收率普遍较低,大幅提高采收率已经成为四川盆地海相页岩气“十四五”(2021—2025年)期间亟需攻关的关键技术问题之一。基于页岩气平台丛式井、长水平段和多簇体积压裂的开发特点,从水平井井控面积、裂缝控制体积和基质采出程度3个方面,系统总结了页岩气提高采收率技术的国内外研究进展,分析了影响采收率的主控因素,梳理了提高采收率面临的技术与科学问题,并给出了相应的攻关建议。研究表明,川南地区页岩气单井产量受水平段长、井间距、压裂参数、生产制度等因素影响,平面和纵向上储量动用率低,裂缝控制体积有限,基质动用程度不高。页岩气提高采收率应以最大程度提高弹性能量利用效率为导向,通过优化簇间距、压裂施工及焖井时间等参数,显著提升裂缝控制体积;通过降低井底压力、优化排采制度、注入CO等手段提高基质采出程度。建议今后重点攻关提高采收率机理和评价模型、基质与裂缝耦合流动机理和数学模型、重复压裂优化工艺参数和注CO提高采收率技术等关键问题,为大幅提高四川盆地页岩气采收率提供理论指导和技术支撑。

The recovery of shale gas is generally low, and achieving a significant increase in the recovery of marine shale gas in Sichuan Basin has become a key technical issue to be tackled during the 14 th Five-Year Plan(2021-2025). Based on the development characteristics of shale gas platform cluster wells, long horizontal sections and multi-cluster volume fracturing, this paper systematically summarizes the domestic and international research progress of shale gas recovery enhancement technology from three aspects: horizontal well control area, fracture control volume and matrix recovery degree, analyzes the main control factors affecting recovery, sorts out the technical and scientific issues regarding recovery enhancement, and gives corresponding suggestions for tackling the problem. The study shows that the single well production of shale gas in southern Sichuan area is affected by the horizontal section length, well spacing, fracture parameters, and production system, with the characteristics of low planar and longitudinal reserve utilization rate, limited fracture control volume and low utilization of matrix. Shale gas recovery enhancement should be oriented to maximize the elastic energy utilization efficiency, significantly improve the fracture control volume by optimizing the cluster spacing, fracture construction parameters and soaking time, and enhance the matrix recovery degree by reducing the bottom hole pressure, optimizing the drainage system and injecting CO. The authors suggest to pay attention to the key issues such as recovery enhancement mechanism and evaluation model, matrix-fracture coupled flow mechanism and evaluation model, repeated fracturing optimization process parameters and the mechanism of recovery enhancement by COinjection, thus providing theoretical guidance and technical support to significantly improve the recovery rate of shale gas in southern Sichuan area.