致密气藏多层砂体合采井产量递减分析方法

Production Decline Analysis for Multi⁃Layer Commingled Production Wells in Tight Gas Reservoirs

致密气藏主力产层多为多层叠置河道砂体,合采时普遍存在各产层贡献不明及砂体动用边界不清的问题。首先,考虑各层河道砂体形态特征和边界尺寸差异,根据等效渗流体积原则,建立了致密气藏多层河道砂体合采井生产模型。其次,基于现代产量递减分析理论,形成了致密气藏多层河道砂体的边界确定方法和合采井产量递减分析图版。最后,讨论不同河道砂体边界距离、砂体数量和砂体位置下的产量递减特征,明确了多层河道砂体对产量递减的影响。研究表明:致密气藏多层河道砂体合采井产量具有5个递减阶段,不稳定流中期阶段可诊断各层砂体边界距离是否相等;河道砂体范围越小,宽砂体数量越少,宽砂体占比越小,储集层稳产能力越差,不稳定流早期阶段和不稳定流中期阶段易出现产量递减速率增大现象。建立的产量递减分析方法可为产层动用程度评价和增产措施制定提供依据。

Main pay zones of tight gas reservoirs are usually multiple layers of stacked channel sandbodies.Commingled production of these layers is commonly challenged by unclear contribution from each layer and undefined boundaries of sandbodies.Considering the morphological characteristics and different boundary sizes of channel sandbodies in the layers,and according to the principle of equivalent flow volume,a model of multi⁃layer commingled production well in tight gas reservoir was established.Then,based on the theory of modern production decline analysis,a method for determining the boundaries of channel sandbodies in tight gas reservoirs was proposed,and the production decline analysis charts for multi⁃layer commingled production wells were plotted.Finally,the production decline was discussed by boundary size,amount,and position of channel sandbodies,and the impacts of multi⁃layer channel sandbodies on production decline were clarified.The study shows that the production deline of multi⁃layer commingled production wells in tight gas reservoirs exhibits five stages.In the middle unsteady flow stage,it is possible to diagnose whether the boundary sizes of the sandbodies in each layer are equal.The smaller the range of channel sandbodies,the fewer the wide sandbodies,the smaller the proportion of wide sandbody,the poorer the sta⁃ble productivity of the reservoir,and the more likely the increase in production decline rate occurs in the early and middle unsteady flow stages.The established method of production decline analysis provides a basis for evaluating the producing degree of each layer and deter⁃mining reservoir stimulation treatments.