基于缝网导流有效性评价的深层页岩气压裂支撑剂优化设计

Optimized design of deep shale gas fracturing proppant based on conductivity effectiveness evaluation of fracture network

深层页岩气储层埋藏深、温度高、地层应力大、岩石塑性强,导致压裂缝网复杂度低,缝网导流能力不足,极大影响了深层页岩气储层的压裂效果。评价深层页岩气压裂缝网的有效性,可以指导深层页岩气储层通过高效地压裂改造获得稳定高产的页岩气产能,具有重要的商业价值。基于川东南丁山地区深层页岩地质条件与裂缝导流能力实验,开展了深层页岩高闭合应力条件下裂缝导流有效性评价。结果表明:随着闭合应力的增大,自支撑裂缝与支撑裂缝导流能力呈快速递减的趋势,当闭合应力达到55 MPa时,自支撑裂缝的导流能力仅为0.1μm^(2)·cm,反映了深层条件下剪切裂缝难以满足流体流动的现状;在铺砂条件下,当闭合应力大于69 MPa时,粒径为40/70目的陶粒可有效满足主裂缝的导流要求,粒径为70/120目的陶粒与石英砂均可达到分支裂缝的导流要求;同时定量计算了满足主裂缝与分支裂缝导流要求的最低铺砂浓度,并绘制了不同类型、粒径的支撑剂用量设计图版。研究成果为深层页岩气储层压裂的支撑剂选择与优化提供了技术参考。

Deep shale gas reservoirs with deep burial,high temperature,high stratigraphic stress and high rock ductility lead to low complexity of fracture network and insufficient fracture network conductivity,causing much impact on effect of deep shale gas reservoir fracturing stimulation.Evaluating effectiveness of deep shale gas reservoir fracture network can conduct efficient fracturing stimulation for high and stable shale gas production,with high commercial value.Based on experiment with geological circumstances and fracture conductivity of deep shale in Dingshan area of southeast Sichuan,fracture conductivity effectiveness in high closure stress regime in deep shale is evaluated.The experiment results show that as closure stress increases,self‑propped fracture and propped fracture conductivity rapidly decrease,and self‑propped fracture conductivity is only 0.1μm^(2)·cm when closure stress achieves 55 MPa,reflecting difficulties of shear fracture in satisfying fluid flow in deep formation.When closure stress is higher than 69 MPa in sand‑laying situation,ceramsite with partical size of 40/70 mesh can effectively satisfy the conductivity requirements of main fracture,and both ceramsite with partical size of 70/120 mesh and quartz sand can satisfy the conductivity requirements of branch fractures.Meanwhile,minimum sanding concentration to satisfy the requirements of main fracture and branch fractures conductivity is quantitatively calculated,and proppant dosage design charts for various kinds and grain sizes are plotted.The study provides technical guide for proppants selection and optimization for deep shale gas reservoirs fracturing.