气水两相流试井复合模型及压力分析

COMPOSITE MODEL AND PRESSURE ANALYSIS OF WELL TEST WITH GAS/WATER BI-PHASE FLOW

文章基于多相流原理,建立了气水两相流试井积分模型。总结了气水两相流的试井曲线规律,分析了压力导数曲线变化的原因。理论分析表明气井即使未见水,气藏气水或油水多相流过渡区内流度的变化可能导致压力导数曲线上翘,然后变平的现象,同时,气水接触前缘是随时间变化的。试井过程中,随着开井时间的增大,气体的降压膨胀,压力波扩散到气水边界以后,水体起到阻止气体移动的作用,导致压力导数曲线上翘。对于出水气井,由于气水总流度随含水饱和度的增大而下降,试井压力导数曲线将发生上翘,导数曲线的上翘斜率与总流度随饱和度下降速度有关。因此不能用单相定压外边界试井模型解释产水气井试井资料。最后分析了1口气井两次试井资料,该井不同阶段试井过程中用多相流动方法确定了气水推进前缘,发现水线逐渐向井移动。

Based on the principle of multi-phase flow, the integral model is developed for well tests with gas/water bi-phase flow. The changing law of well test curves with gas/water bi-phase flow is summed. The reasons why the pressure derivative curves change are analyzed. The theoretical analysis shows it may cause the pressure derivative curves going up then flattening due to the mobility change in the transition zone of gas/water or oil/water multi-phase flow of the gas reservoir even though no water producing from the gas wells. Also, the gas/water contact front changes with time. During the well test, as the well opening time increases and the gas expands because the pressure drops, the aquifer blocks the movement of gas when the pressure wave reaches the gas/water boundary, which causes the pressure derivative curves going up. As for the gas wells with water producing, the pressure derivative curves of the well tests will go up since the total gas/water mobility will decrease as the water saturation increases. The slope of the derivative curve is related with the total mobility-decreasing rate as the saturation decreases. Therefore, the well testing data of gas wells with water producing can't be interpreted by the well test model of single phase and boundary with constant pressure. Finally, the 2 sets of well test data for the same well are analyzed. The multi-phase flow method is used to determine the gas/water front at the different stages during the well test for the well. It is found the water front moves to the borehole gradually.