共和盆地干热岩体人工裂隙带结构的控热机理与产能优化

Heat control mechanism and productivity optimization of artificial fracture zone structure of dry hot rock in Gonghe Basin

人工压裂是获取干热岩型地热资源的关键环节,压裂后的人工裂隙带结构对开采条件下水热传递过程具有重要控制作用。结合我国共和盆地干热岩储层地质条件,采用数值模拟方法着重分析干热岩不同产状人工裂隙带的渗透率与宽度对热储中水热传递过程的影响机理,明确不同人工裂隙结构条件下水热产出能力,进而优化井间距。结果表明:当人工裂隙带渗透率较小时(小于5 D),裂隙带规模越大,开采井温度越高;当渗透率较大时(大于10 D),在水平裂隙带中,随着裂隙带规模的增加,由于注入冷水的快速扩散导致整体低温区域增加,开采井温度反而降低。在水平裂隙带中注入冷水主要为水平向流动,随着渗透率的增加,开采井温度更易受注入冷水的影响而降低;但在垂直裂隙带及倾斜裂隙带中,随着渗透率的增加,垂向自由对流增强,注入冷水更易于向储层底部高温区域流动,经加热后到达开采井,使得开采温度提升。综合比较,同一井间距条件下,低渗水平裂隙带以及高渗垂直裂隙带的产热能力较其他裂隙带更强。

Hydraulic fracturing is necessary to obtain geothermal energy from the hot dry rocks.The structure of the artificial fractures plays an important role in controlling the water and heat transport during the heat production.In this study,we analyzed the influence of the permeability and width of artificial fracture zone on the coupled heat and flow processes in the Gonghe Basin,China.The results showed that in the fractured reservoir with permeability lower than 5 D,the outflow temperature increases with the width of the fracture zones.This is because the injected cold water can sufficiently merge with the thermal water in the reservoir,and has a weak influence on the water temperature close to the extraction well.A special situation occurs in the horizontal reservoir with permeability higher than 10 D,where the outflow temperature decreases with the increase of fracture zone width,because the overall low temperature zone is increased due to the rapid diffusion of injected cold water.In the reservoir with horizontal fracture zone,outflow temperature decreases with the increase of the permeability,because the injected cold water easily arrives the production well.In contrast,in the vertical or tilted fracture reservoir,the outflow temperature increases with the permeability,because the free convection occurs strongly in the high-permeable reservoirs.A synthetic comparison suggested that under the same well distance,heat production is higher in the reservoirs with low-permeable horizontal fracture zone and with high-permeable vertical fracture zone,among other fracture zones.