Investigation of low water recovery based on gas-water two-phase low-velocity Non-Darcy flow model for hydraulically fractured horizontal wells in shale

Various mechanisms are employed to interpret the low water recovery during the shale-gas production period,such as extra-trapped water in the fracture network,water imbibition due to osmotic pressure and capillary pressure.These lead to the difficulty of water flow,which could be described by lowvelocity non-Darcy's law known as threshold pressure gradient(TPG).In this paper we firstly employ the low-velocity non-Darcy's law to describe the water flow and use Darcy flow accounting for slip flow and free molecular flow mechanisms to model gas flow in the shale formation.The sensitive study using numerical simulation shows that the proposed flow model could model the low fracturing liquid recovery and that large pseudo TPG leads to lower fracturing liquid recovery.Thus,the proposed model would give new insight to model the low water recovery in shale formations.

欠压实低速泥岩对地震反射及AVO的影响

莺歌海盆地高温高压地层由于晚期快速沉降和快速沉积形成了巨厚的欠压实低速泥岩带,目前东方区中深层已发现多个高温高压气藏,其岩石物理规律清晰,气层顶面地震反射特征以强振幅波谷反射为主,AVO特征明显。然而,乐东区高温高压地层地震反射特征与东方区截然不同,AVO特征复杂,严重制约了乐东区高温高压气藏的勘探。从区域地震岩石物理统计规律出发,总结了乐东区地震反射振幅和AVO特征的影响因素,研究发现,乐东区高温高压地层欠压实趋势复杂,低速泥岩速度变化范围大,直接影响气层顶面的地震反射特征和AVO特征。AVO理论模拟表明,受上覆低速泥岩速度范围的影响,AVO-孔隙度模板发生明显变化,通过分析上覆低速泥岩的速度,可以有效预测储层的孔隙度大小,实际钻井结果验证了该方法预测孔隙度的有效性,为莺歌海盆地乐东区高温高压地层下一步有利目标搜寻和勘探提供了有效的指导。