合采条件下低压储层内流体运移特性试验研究

Physical simulation experiment on flow characteristics in a low-pressure reservoir under co-production

为了研究多层合采条件下不同阶段内低压储层内流体流动特征,通过搭建物理模拟试验平台和构建流体流动参数计算原理,开展了一井四层物理模拟试验。结果表明:速度和偏转角与流体流动起点的位置有关,当流动起点和井筒中心连线与水平方向夹角从0°转换为90°的过程中,水平速度分量所占的比例减小,而垂向速度分量则增加,井筒内的合流效应致使煤储层中心区域的流体流速有一定程度的衰减。基于合采条件下低压储层存在的层间干扰现象,将合采过程划分为非扰动阶段和扰动阶段。在非扰动阶段内,随着流动起点距井筒中心距离的减小,流体流动方向趋于接近流动最佳趋势线,偏转角趋于0°。距井筒远端流体流动轨迹近似平行,呈现平行流动,而在井筒近端的流体整体流动趋势呈现径向流动。在扰动阶段内,各分层产生的流体在井筒内相互作用形成的流场压力高于低压储层压力时,促使流体侵入低压储层,改变了储层内流体流动方向,使低压储层内出现反向流动。随着流体流动起点距井筒中心距离的减小,流动方向与接近流动最佳趋势线夹角趋于180°,而其以井筒为中心以辐射的形式向储层四周流动。产层组合时,应选择层间压差较小的煤储层进行合采,优化合采兼容性,减弱各煤储层受到干扰的程度,避免低压储层出现倒灌和产气抑制现象。

To study the flow characteristics in a low-pressure reservoir under co-production conditions,a“one well with four layers”physical simulation was performed by constructing a physical simulation experimental platform and evaluating the calculation principles of the flow characteristic parameters.The results indicate that the flow velocity and deflection angle are related to the position of the flow starting point.As the angle between the line from the flow starting point to the wellbore and the horizontal direction changes from 0°to 90°,the horizontal velocity component gradually decreases,and the vertical velocity component gradually increases until it becomes dominant.The confluence effect in the wellbore results in a decrease in velocity,to a certain extent,in the central area of the reservoir.Based on the phenomenon of interlayer interference in a low-pressure reservoir under co-production,this entire process can be divided into a non-disturbance stage and disturbance stage.In the non-disturbance stage,with a decrease in the distance between the flow starting point and the wellbore,the flow direction converges toward the best trend line direction,and the deflection angle trends toward 0°.The flow path far from the wellbore is approximately parallel and exhibits parallel flow,whereas the overall flow trend near the wellbore is influenced by the area around the wellbore and exhibits radial flow.In the disturbance stage,when the pressure of the flow field,formed by the interactions between the fluids produced by each layer in the wellbore,is greater than the reservoir pressure in the low-pressure reservoir,gas invades the low-pressure reservoir and changes the direction of flow in the reservoir.When the distance between the flow starting point and the wellbore decreases,the deflection angle between the flow direction and the best trend line direction trends toward 180°.Additionally,the flow takes the form of radiation from the wellbore to the surrounding reservoir.In production layer combination,the coal reservoirs with small interlayer pressure differences should be selected to optimize the co-producing compatibility,reduce the interference degree of each coal reservoir,and avoid the phenomenon of backflow and gas production inhibition in low-pressure reservoirs.