Characteristics and significance of proppant in hydraulic fractures in coal reservoirs
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摘要: 煤层水力压裂后支撑剂的展布形态及内部特征在很大程度上决定压裂效果的优劣。以煤矿井下巷道中揭露的煤层气井压裂裂缝内的支撑剂为研究对象,重点观察并分析支撑剂的形貌和堆积特征及其与堆积过程的关系。再以压裂裂缝典型部位获取的支撑剂为实例,描述支撑剂的形貌与堆积特征,还原支撑剂的堆积过程。结果表明:在水平缝内,距井筒距离增加,支撑剂粒径逐渐变细,其中软煤带内的支撑剂颗粒在沉积前经历了强烈的碰撞和复杂的水动力环境,并形成支撑剂带-支撑剂与煤粉混合带-煤粉带的三带铺砂特征;裂缝延伸形式转变易导致支撑剂提前沉积,不利于裂缝延伸;不同裂缝部位内支撑剂颗粒的分选性、完整性、煤粉附着状况以及裂缝壁面痕迹往往不同,对支撑剂的堆积过程和压裂流体的流动特征具有指示意义。研究成果为仿真模拟实验的参数设定和生产实践提供科学依据。同时,对现场同类型压裂施工设计及压裂效果预测具有一定的借鉴意义。Abstract: The distribution form and internal characteristics of proppant after coal seam hydraulic fracturing determine the fracturing effect to a great extent. The proppant in the hydraulic fracture exposed in the underground roadways of the coal mine is taken as the research object. The morphology and accumulation characteristics of the proppant were observed, and the relationship between the morphology and accumulation characteristics of the proppant and its stacking process was analyzed. Then, the morphology and accumulation characteristics of the proppant obtained at the typical part of the hydraulic fracture are described, which provides a basis that restores the stacking process of the proppant. The results of this study indicate that the proppant size gradually becomes smaller with the increase of the distance from the wellbore in the horizontal fracture. In the soft coal zone, the proppant particles experience a strong collision in chaotic hydrodynamic circumstances before deposition, and the sand spreading characteristics of the proppant zone, mixed zone of proppant and pulverized coal, and coal pulverized zone are formed. The change of fracture extension form can lead to the early deposition of proppant, which is not conducive to fracture extension. The sorting and integrity of proppant particles, the adhesion of pulverized coal and the trace in coal rock are often different in different fractures, which is of guiding significance to the proppant accumulation process and the flow characteristics of fracturing fluid. The results can provide a scientific basis for the parameter of numerical simulation and engineering practice. And it has certain reference significance for the same type of fracturing design and fracturing effect prediction.
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表 1 水平缝内各取样点支撑剂颗粒粒径分布
Table 1 Particle size distribution of the proppant at each sampling point in the horizontal hydraulic fracture
取样位置 总颗粒数 d>1.7 mm 1.7 mm≤d≤1.18 mm d<1.18 mm 水泥环 77 13 61 3 取样点1 87 13 71 3 取样点2 40 8 29 3 取样点3 81 2 77 2 -
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