深部煤层气定向压裂孔/簇间流量及支撑剂分配特征

Inter-cluster and intra-cluster flow distribution and proppant allocation in deep coalbed methane orientation fracturing

  • 摘要: 我国深部煤层气资源丰富,开发利用潜力巨大,有望成为我国天然气供应的重要补充。但是,当前深部煤层气开发工艺尚处于探索阶段,储层改造主要采用大规模体积压裂工艺,存在产气效果差异大、产量递减速度快的问题,缺乏与地质条件精准配套的增产技术体系。“定向射孔+靶向控缝+精细压裂”有望成为深部煤层气地质适配性的压裂工艺方法。提出了7种深煤层水平井定向射孔布孔模式:定向水平向、4点—8点定向向下、扇面定向向下(向上)、扇面定向向下(向上)+水平向(240°布孔)、直线定向向下(向上)。为了研究定向射孔模式下深煤层水平井孔/簇间进液、进砂分布的均衡性,采用计算流体动力学与离散元耦合方法(CFD-DEM),建立了水平井筒颗粒运移流固耦合模型,研究了不同定向射孔布孔模式、排量、砂比、段内簇数、组合粒径支撑剂影响下,段内簇间及簇内孔间流量分配及支撑剂分布特征。结果表明:不同定向射孔方式下孔/簇间流量与支撑剂分配均匀性各异,其中240°定向射孔(扇面向下或向上+水平方向)孔间流量分配均匀性较好,240°定向射孔和4点—8点定向向下射孔孔间支撑剂分配均匀性较好。大排量( > 16 m3/min)、控砂比(携砂液阶段最高砂比 < 25%)、提升小粒径支撑剂占比(0.212/0.109 mm∶0.380/0.212 mm∶0.550/0.270 mm = 6∶3∶1)、段内3~4簇,有利于孔/簇间流量与支撑剂的均匀分布,提升储层改造的均衡性。鄂尔多斯盆地东缘深部煤层气现场应用表明定向射孔产气量高于常规螺旋射孔,“扇面向下+水平向(240°布孔)”定向射孔增产效果最显著。建议深部煤层气储层改造根据井眼轨迹在煤层中的位置(特别是与亮煤的相对位置),开展“一簇一策”射孔设计,诱导裂缝定向起裂、靶向沟通“地质−工程”双甜点,实现“定向导控、差异改造、有效加砂、饱和支撑”的改造目的。研究结果有望为深部煤层气优质高效压裂提供理论基础与参数借鉴。

     

    Abstract: China has abundant deep coalbed methane (CBM) resources with significant potential for development and utilization, which is expected to become an important supplement to national natural gas supply. However, the current deep CBM development technology is still in the exploratory status, and the reservoir stimulation mainly relies on massive fracturing, which suffers from significant differences in gas production rate and rapid production declines. The major reason behind is the lack of a stimulation technology that precisely matches geological conditions. “Orientation perforating + targeted fracture controlling + precision fracturing” is expected to become an effective fracturing method that is geologically compatible with deep CBM. This paper proposes seven orientation perforating patterns for deep coalbed horizontal wells: directional horizontal, 4 o'clock—8 o'clock orientation downward, fan-shaped orientation downward (upward), fan-shaped orientation downward (upward) + horizontal (240° perforation pattern), and straight upward orientation (downward). To investigate the uniformity of fluid and proppant distribution between and within clusters in deep coalbed horizontal wells under different orientation perforating patterns, this paper utilizes a coupled computational fluid dynamics and discrete element method (CFD-DEM). A fluid-particle transport fluid-solid coupling model for horizontal wellbores is established. The study examines the characteristics of inter-cluster and intra-cluster flow distribution and proppant distribution under different orientation perforating patterns, flow rates, sand ratios, cluster numbers within one stage, and graded proppant injection. The results show that the uniformity of flow and proppant distribution varies under different orientation perforating methods. The 240° orientation perforating (fan shape down or up + horizontal direction) shows better uniformity in flow distribution between holes, and the 240° orientation perforating and 4 o'clock—8 o'clock orientation downward perforating show better uniformity in proppant distribution between holes. High pumping rates (> 16 m3/min), low sand ratios (maximum sand ratio during the sand carrying stage < 25%), a higher proportion of smaller particle-sized proppants (0.212/0.109 mm∶0.380/0.212 mm∶0.550/0.270 mm = 6∶3∶1), and 3 to 4 clusters within a stage are conducive to the uniform distribution of flow and proppant between holes/clusters, enhancing the balance of reservoir stimulation. Field applications in the eastern margin of the Ordos Basin for deep CBM have shown that orientation perforating yields higher gas production than conventional spiral perforating, with the “fan shape down + horizontal direction (240° pattern)” orientation perforating showing the most significant increasing in gas production. It is recommended that deep CBM reservoir stimulation be designed based on the position of the well trajectory within the coal seam (especially its relative position to bright coal), implementing a “one-cluster one-policy” perforating design to induce directional fracture initiation, targeted communication with the "geological-engineering" sweet spots, and achieve the stimulation objectives of “directed guidance, differential stimulation, effective proppant placement and saturated support”. The key findings are expected to provide theoretical foundations and parameter references for high-quality and efficient fracturing in deep CBM wells.

     

/

返回文章
返回