页岩气藏压裂支撑裂缝的有效性评价

为了了解、掌握页岩气藏清水压裂缝网能够提供的导流能力大小及裂缝的有效性，利用四川盆地某构造的页岩进行了室内裂缝导流能力测试。实验结果表明：支撑剂浓度不足单层的情况时，闭合压力低于30 MPa，导流能力可与一定量的高浓度（多层）情况相当，但支撑剂嵌入和破碎显著增加，其导流能力不稳定，随时间增加可持续降低，闭合压力40 MPa时，20/40目陶粒嵌入程度可达71.8%，闭合压力进一步增大，裂缝将闭合失效；较低硬度的页岩支撑剂嵌入严重，导致低支撑剂浓度裂缝残余支撑缝宽不足，仅增加支撑剂粒径不足以克服嵌入影响，裂缝内需要有足够的支撑剂浓度，形成的缝网不能过于复杂；页岩黏土含量高，支撑剂充填层泥化严重，对支撑裂缝有效性的伤害不容忽视，可变形的树脂覆膜砂在一定程度上解决了支撑剂嵌入和充填层泥化问题。

Assessment on the effectiveness of propped fractures in the fracturing of shale gas reservoirs

For the purpose of understanding the conductivity performance and the fracture effectiveness of the clean water fracturing network in shale gas reservoirs,an indoor test on fracture conductivity is done by selecting the shale samples from a certain structure in the Sichuan Basin.The following findings are concluded from the test results.When the proppant concentration is insufficient for monolayer and the closure pressure is under 30 MPa,the conductivity is similar to that in higher concentration(multi-layers).However,the conductivity is not stable and tends to decline constantly over time.When the closure pressure goes up to 40 MPa,the embedment degree of 20/40 mesh ceramic proppant can be 71.8%.The fracture may close up and lose all conductivity when the pressure increases further.The embedment problem is more detrimental for shale rocks with less hardness,resulting in low proppant concentration and insufficient width of propped residual fracture,which can not be overcome by greater grain size of proppant.Besides,the proppant concentration should be high enough in the fractures and the fracture network formed should not be too complex.If the clay content is high in shale,the proppant pack suffers from greater argillization,which may result in significant damage to fracture effectiveness.The problem of embedment and argillization can be resolved to some degree by using the deformable resin coated proppant.